// Copyright (c) 2016-2021 Fabian Schuiki

//! Name resolution.
//!
//! This module implements the infrastructure to describe scopes and resolve
//! names in them.

use crate::crate_prelude::*;
use crate::{
    ast::AnyNode,
    ast_map::AstNode,
    common::{SessionContext, Verbosity},
    hir::HirNode,
    port_list::{self, AsPortedNode},
    ParamEnv,
};
use std::{
    collections::HashMap,
    hash::{Hash, Hasher},
    sync::Arc,
};

/// One local scope.
///
/// A rib represents a any kind of scope. Ribs form a tree structure along their
/// parents that may be traversed from the bottom to the top to perform name
/// resolution, or top to bottom to lookup hierarchical names.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Rib {
    /// The node this rib is associated with.
    ///
    /// When querying the compiler for a node's rib, what you get in return is
    /// not necessarily the rib of that node. If the node does not generate a
    /// new rib, you get back the rib of a parent node.
    pub node: NodeId,
    /// The parent rib.
    ///
    /// Note that this does not necessarily correspond to the parent node, but
    /// may skip nodes that do not contain a rib.
    pub parent: Option<NodeId>,
    /// The data associated with the rib.
    pub kind: RibKind,
}

/// A local scope kind.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum RibKind {
    /// A normal declaration.
    Normal(Spanned<Name>, NodeId),
    /// A module.
    Module(HashMap<Name, NodeId>),
    /// An enum type declaration.
    Enum(HashMap<Name, NodeId>),
    /// An imported rib.
    Import(Box<Rib>),
}

impl Rib {
    /// Look up a name.
    pub fn get(&self, name: Name) -> Option<NodeId> {
        self.kind.get(name)
    }

    /// Resolve import ribs to the imported rib.
    pub fn resolve_imports(&self) -> &Self {
        match &self.kind {
            RibKind::Import(rib) => rib.as_ref(),
            _ => self,
        }
    }
}

impl RibKind {
    /// Look up a name.
    pub fn get(&self, name: Name) -> Option<NodeId> {
        match *self {
            RibKind::Normal(n, id) if n.value == name => Some(id),
            RibKind::Module(ref defs) | RibKind::Enum(ref defs) => defs.get(&name).cloned(),
            _ => None,
        }
    }
}

/// Determine the local rib that applies to a node.
///
/// This will return either the rib the node itself generates, or the next rib
/// up the hierarchy.
#[moore_derive::query]
pub(crate) fn local_rib<'a>(cx: &impl Context<'a>, node_id: NodeId) -> Result<&'a Rib> {
    let ast = cx.ast_of(node_id)?;
    trace!("local_rib for {} ({:?})", ast.desc_full(), node_id);
    let mut parent = None;
    let mut kind = match ast {
        AstNode::TypeParam(_, decl) => Some(RibKind::Normal(decl.name, node_id)),
        AstNode::ValueParam(_, decl) => Some(RibKind::Normal(decl.name, node_id)),
        AstNode::Module(_) => Some(RibKind::Module(HashMap::new())),
        AstNode::VarDecl(decl, _, _) | AstNode::NetDecl(decl, _, _) => Some(RibKind::Normal(
            Spanned::new(decl.name, decl.name_span),
            node_id,
        )),
        AstNode::GenvarDecl(decl) => Some(RibKind::Normal(decl.name, node_id)),
        AstNode::Stmt(stmt) => match stmt.kind {
            ast::VarDeclStmt(_) => {
                let hir = match cx.hir_of(node_id)? {
                    HirNode::Stmt(x) => x,
                    _ => unreachable!(),
                };
                match hir.kind {
                    hir::StmtKind::InlineGroup { rib, .. } => return cx.local_rib(rib),
                    _ => None,
                }
            }
            _ => None,
        },
        AstNode::Package(_) => Some(RibKind::Module(HashMap::new())),
        AstNode::Type(_) => {
            let hir = match cx.hir_of(node_id)? {
                HirNode::Type(x) => x,
                _ => unreachable!(),
            };
            local_rib_kind_for_type(cx, &hir.kind)
        }
        AstNode::Import(import) => {
            let pkg_id = match cx.gcx().find_package(import.pkg.value) {
                Some(id) => id,
                None => {
                    cx.emit(
                        DiagBuilder2::error(format!("`{}` not found", import.pkg.value))
                            .span(import.pkg.span),
                    );
                    return Err(());
                }
            };
            if let Some(name) = import.name {
                trace!(
                    "Importing single `{}` from `{}`: {}",
                    name,
                    import.pkg,
                    cx.ast_of(pkg_id)?.desc_full()
                );
                let resolved = cx.resolve_downwards_or_error(name, pkg_id)?;
                let rib = cx.local_rib(resolved)?;
                Some(RibKind::Import(Box::new(rib.clone())))
            } else {
                let rib = cx.hierarchical_rib(pkg_id)?;
                trace!("Importing entire `{}`: {:#?}", import.pkg, rib);
                Some(RibKind::Import(Box::new(rib.clone())))
            }
        }
        AstNode::SubroutineDecl(decl) => Some(RibKind::Normal(decl.prototype.name, node_id)),
        _ => None,
    };
    if kind.is_none() {
        let hir = cx.hir_of(node_id)?;
        kind = match hir {
            HirNode::Typedef(def) => {
                parent = Some(def.ty);
                Some(RibKind::Normal(
                    Spanned::new(def.name.value, def.name.span),
                    node_id,
                ))
            }
            HirNode::IntPort(port) => Some(RibKind::Normal(port.name, node_id)),
            _ => None,
        };
    }
    let kind = match kind {
        Some(kind) => kind,
        None => {
            return cx.local_rib(
                cx.parent_node_id(node_id)
                    .expect("root node must produce a rib"),
            );
        }
    };
    let rib = Rib {
        node: node_id,
        parent: match parent.or_else(|| cx.parent_node_id(node_id)) {
            Some(parent_id) => Some(cx.local_rib(parent_id)?.node),
            None => None,
        },
        kind: kind,
    };
    if cx.sess().has_verbosity(Verbosity::NAMES) {
        let mut d = DiagBuilder2::note(format!(
            "created local rib for {}",
            cx.ast_of(node_id)?.desc_full()
        ))
        .span(cx.span(node_id))
        .add_note(format!("{:?}", rib.kind));
        if let Some(parent) = rib.parent {
            d = d
                .add_note("Parent is here:".to_string())
                .span(cx.span(parent));
        }
        cx.emit(d);
    }
    Ok(cx.arena().alloc_rib(rib))
}

fn local_rib_kind_for_type<'gcx>(cx: &impl Context<'gcx>, kind: &hir::TypeKind) -> Option<RibKind> {
    trace!("creating local rib for type {:#?}", kind);
    match kind {
        hir::TypeKind::PackedArray(inner, ..) => local_rib_kind_for_type(cx, inner.as_ref()),
        hir::TypeKind::Enum(ref variants, _) => Some(RibKind::Enum(
            variants
                .iter()
                .map(|(name, id)| (name.value, *id))
                .collect(),
        )),
        _ => None,
    }
}

/// Determine the hierarchical rib of a node.
///
/// This will return a rib containing the hierarchical names exposed by a node.
#[moore_derive::query]
pub(crate) fn hierarchical_rib<'a>(cx: &impl Context<'a>, node_id: NodeId) -> Result<&'a Rib> {
    let hir = cx.hir_of(node_id)?;
    let mut names = HashMap::new();
    let mut rib_id = match hir {
        HirNode::Package(pkg) => Some(pkg.last_rib),
        HirNode::Module(module) => Some(module.last_rib),
        _ => panic!("{} has no hierarchical rib", hir.desc_full()),
    };
    while let Some(id) = rib_id {
        let rib = cx.local_rib(id)?;
        match rib.kind {
            RibKind::Normal(name, def) => {
                names.insert(name.value, def);
            }
            RibKind::Module(ref defs) => names.extend(defs),
            RibKind::Enum(ref defs) => names.extend(defs),
            RibKind::Import(_) => (), // imports are never visible
        }
        rib_id = rib.parent;
        if rib_id == Some(node_id) {
            rib_id = None;
        }
    }
    let rib = Rib {
        node: node_id,
        parent: None,
        kind: RibKind::Module(names),
    };
    Ok(cx.arena().alloc_rib(rib))
}

/// Resolve a name upwards through the ribs.
///
/// This is equivalent to performing regular scoped namespace lookup.
#[moore_derive::query]
pub(crate) fn resolve_upwards<'a>(
    cx: &impl Context<'a>,
    name: Name,
    start_at: NodeId,
) -> Result<Option<NodeId>> {
    // Get the AST associated with the node ID and map it to an AnyNode.
    let ast = cx.ast_of(start_at)?;
    let node = match ast.get_any() {
        Some(x) => x,
        None => bug_span!(
            cx.span(start_at),
            cx,
            "resolve_upwards called on node which doesn't implement AnyNode yet: {:?}",
            ast
        ),
    };
    cx.resolve_local(name, cx.scope_location(node), false)
        .map(|def| def.map(|def| def.node.id()))
}

/// Resolve a name downwards.
///
/// This is equivalent to performing a hierarchical name lookup.
#[moore_derive::query]
pub(crate) fn resolve_downwards<'a>(
    cx: &impl Context<'a>,
    name: Name,
    start_at: NodeId,
) -> Result<Option<NodeId>> {
    // Get the AST associated with the node ID and map it to a ScopedNode.
    let ast = cx.ast_of(start_at)?;
    let node = match ast.get_any().and_then(|n| n.as_all().get_scoped_node()) {
        Some(x) => x,
        None => bug_span!(
            cx.span(start_at),
            cx,
            "resolve_downwards called on node which doesn't implement ScopedNode yet: {:?}",
            ast
        ),
    };
    Ok(cx.resolve_namespace(name, node).map(|def| def.node.id()))
}

/// Resolve a node to its target.
#[moore_derive::query]
pub(crate) fn resolve_node<'a>(
    cx: &impl Context<'a>,
    node_id: NodeId,
    env: ParamEnv,
) -> Result<NodeId> {
    let hir = cx.hir_of(node_id)?;
    match hir {
        HirNode::Expr(expr) => match expr.kind {
            hir::ExprKind::Ident(ident) => return cx.resolve_upwards_or_error(ident, node_id),
            hir::ExprKind::Scope(scope_id, name) => {
                let within = cx.resolve_node(scope_id, env)?;
                return cx.resolve_downwards_or_error(name, within);
            }
            _ => (),
        },
        HirNode::Type(ty) => match ty.kind {
            hir::TypeKind::Named(name) => return cx.resolve_upwards_or_error(name, node_id),
            hir::TypeKind::Scope(scope_id, name) => {
                let within = cx.resolve_node(scope_id, env)?;
                return cx.resolve_downwards_or_error(name, within);
            }
            _ => (),
        },
        HirNode::IntPort(port) if port.data.is_none() => {
            return cx
                .resolve_hierarchical_or_error(
                    port.name,
                    port.node.as_all().get_scoped_node().unwrap(),
                )
                .map(|def| def.node.id());
        }
        _ => (),
    }
    error!("{:#?}", hir);
    cx.emit(DiagBuilder2::bug("cannot resolve node").span(hir.human_span()));
    Err(())
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct StructDef {
    pub packed: bool,
    pub fields: Vec<StructField>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct StructField {
    pub name: Spanned<Name>,
    pub ty: NodeId,
    pub field: NodeId,
}

/// Obtain the details of a struct definition.
#[moore_derive::query]
pub(crate) fn struct_def<'a>(cx: &impl Context<'a>, node_id: NodeId) -> Result<Arc<StructDef>> {
    let hir = cx.hir_of(node_id)?;
    let struct_fields = match hir {
        HirNode::Type(hir::Type {
            kind: hir::TypeKind::Struct(ref fields),
            ..
        }) => fields,
        _ => {
            cx.emit(
                DiagBuilder2::error(format!("{} is not a struct", hir.desc_full()))
                    .span(hir.human_span()),
            );
            return Err(());
        }
    };
    let fields = struct_fields
        .iter()
        .flat_map(|&id| match cx.hir_of(id) {
            Ok(HirNode::VarDecl(vd)) => Some(StructField {
                name: vd.name,
                ty: vd.ty,
                field: id,
            }),
            _ => None,
        })
        .collect();
    Ok(Arc::new(StructDef {
        packed: true,
        fields,
    }))
}

/// Resolve the field name in a field access expression.
///
/// Returns the index of the field that is actually being accessed, and a
/// reference to the member itself.
#[moore_derive::query]
pub(crate) fn resolve_field_access<'a>(
    cx: &impl Context<'a>,
    node_id: NodeId,
    env: ParamEnv,
) -> Result<(usize, &'a ty::StructMember<'a>)> {
    let hir = match cx.hir_of(node_id)? {
        HirNode::Expr(x) => x,
        _ => unreachable!(),
    };
    let (target_id, name) = match hir.kind {
        hir::ExprKind::Field(target_id, name) => (target_id, name),
        _ => unreachable!(),
    };

    let ty = cx.type_of(target_id, env)?;
    let strukt = if let Some(strukt) = ty.get_struct() {
        strukt
    } else {
        let mut d = DiagBuilder2::error(format!("value of type `{}` is not a struct", ty))
            .span(hir.human_span());
        if ty.resolve_full() != ty {
            d = d.add_note(format!("`{}` is defined as `{}`", ty, ty.resolve_full()));
        }
        cx.emit(d);
        return Err(());
    };

    let index = strukt
        .members
        .iter()
        .position(|member| member.name.value == name.value);
    match index {
        Some(x) => Ok((x, &strukt.members[x])),
        None => {
            cx.emit(
                DiagBuilder2::error(format!("value of type `{}` has no field `{}`", ty, name))
                    .span(name.span())
                    .add_note(format!("`{}` was defined here:", ty))
                    .span(strukt.ast.span()),
            );
            Err(())
        }
    }
}

/// Determine the scope generated by a node.
pub fn generated_scope_id<'gcx>(
    cx: &impl Context<'gcx>,
    node_id: NodeId,
) -> Result<&'gcx Scope<'gcx>> {
    let ast = cx.ast_of(node_id)?;
    Ok(match ast {
        AstNode::Module(node) => cx.generated_scope(node),
        AstNode::Package(node) => cx.generated_scope(node),
        _ => bug_span!(ast.span(), cx, "node does not generate a scope"),
    })
}

/// Marker trait for AST nodes that generate a scope.
pub trait ScopedNode<'a>: ast::AnyNode<'a> {}
impl<'a> ScopedNode<'a> for ast::Root<'a> {}
impl<'a> ScopedNode<'a> for ast::SourceFile<'a> {}
impl<'a> ScopedNode<'a> for ast::Module<'a> {}
impl<'a> ScopedNode<'a> for ast::Interface<'a> {}
impl<'a> ScopedNode<'a> for ast::Package<'a> {}
impl<'a> ScopedNode<'a> for ast::Stmt<'a> {}
impl<'a> ScopedNode<'a> for ast::Procedure<'a> {}
impl<'a> ScopedNode<'a> for ast::ClassDecl<'a> {}
impl<'a> ScopedNode<'a> for ast::SubroutineDecl<'a> {}
impl<'a> ScopedNode<'a> for ast::GenerateFor<'a> {}
impl<'a> ScopedNode<'a> for ast::GenerateIf<'a> {}
impl<'a> ScopedNode<'a> for ast::GenerateCase<'a> {}
impl<'a> ScopedNode<'a> for ast::GenerateBlock<'a> {}

// Compare and hash scoped nodes by reference for use in the query system.
impl<'a> Eq for &'a dyn ScopedNode<'a> {}
impl<'a> PartialEq for &'a dyn ScopedNode<'a> {
    fn eq(&self, other: &Self) -> bool {
        std::ptr::eq(self.as_ptr(), other.as_ptr())
    }
}
impl<'a> Hash for &'a dyn ScopedNode<'a> {
    fn hash<H: Hasher>(&self, h: &mut H) {
        std::ptr::hash(self.as_ptr(), h)
    }
}

/// Anything that can be converted to a `ScopedNode`.
pub trait AsScopedNode<'a> {
    /// Return this node as a `ScopedNode`, or `None` if it generates no scope.
    fn get_scoped_node(&self) -> Option<&'a dyn ScopedNode<'a>>;

    /// Check if this node is a `ScopedNode`.
    fn is_scoped_node(&self) -> bool {
        self.get_scoped_node().is_some()
    }
}

impl<'a> AsScopedNode<'a> for ast::AllNode<'a> {
    fn get_scoped_node(&self) -> Option<&'a dyn ScopedNode<'a>> {
        match *self {
            // This should reflect the impl trait list above!
            ast::AllNode::Root(x) => Some(x),
            ast::AllNode::SourceFile(x) => Some(x),
            ast::AllNode::Module(x) => Some(x),
            ast::AllNode::Interface(x) => Some(x),
            ast::AllNode::Package(x) => Some(x),
            ast::AllNode::Stmt(x) => match x.kind {
                ast::SequentialBlock(..)
                | ast::ParallelBlock(..)
                | ast::IfStmt { .. }
                | ast::CaseStmt { .. }
                | ast::ForeverStmt(..)
                | ast::RepeatStmt(..)
                | ast::WhileStmt(..)
                | ast::DoStmt(..)
                | ast::ForStmt(..)
                | ast::ForeachStmt(..) => Some(x),
                _ => None,
            },
            ast::AllNode::Procedure(x) => Some(x),
            ast::AllNode::ClassDecl(x) => Some(x),
            ast::AllNode::SubroutineDecl(x) => Some(x),
            ast::AllNode::GenerateFor(x) => Some(x),
            ast::AllNode::GenerateIf(x) => Some(x),
            ast::AllNode::GenerateCase(x) => Some(x),
            ast::AllNode::GenerateBlock(x) => Some(x),
            _ => None,
        }
    }
}

/// Determine the scope generated by a node.
#[moore_derive::query]
pub(crate) fn generated_scope<'a>(
    cx: &impl Context<'a>,
    node: &'a dyn ScopedNode<'a>,
) -> &'a Scope<'a> {
    // Find the parent scope.
    let parent = node
        .get_parent()
        .map(|_| cx.scope_location(node.as_any()).scope);

    // Create a new scope generator which will traverse the AST.
    let mut gen = ScopeGenerator::new(
        cx,
        Scope {
            node,
            parent,
            defs: Default::default(),
            wildcard_imports: Default::default(),
            subscopes: Default::default(),
        },
    );
    debug!("Generating scope {:?}", node);

    // Add definitions for the analyzed ports.
    if let Some(node) = node.as_all().get_ported() {
        for node in &cx.canonicalize_ports(node).int {
            // Skip ports which are not definitions themselves, but reference
            // another definition in the body.
            if node.data.is_some() {
                gen.add_def(Def {
                    node: DefNode::IntPort(node),
                    name: node.name,
                    vis: DefVis::LOCAL | DefVis::HIERARCHICAL,
                    may_override: true,
                    ordered: false,
                });
            }
        }
    }

    // Gather the definitions.
    node.accept(&mut gen);

    // If this is the AST root, pull up `GLOBAL` definitions from the subscopes.
    if node.as_all().is_root() {
        trace!("Pulling up global defs from subscopes");
        for node in gen.scope.subscopes.clone() {
            let scope = cx.generated_scope(node);
            for &def in scope.defs.values() {
                gen.add_def(def);
            }
        }
    }

    // Allocate the scope into the arena and return it.
    trace!("Generated scope {:#?}", gen.scope);
    cx.gcx().arena.alloc_scope(gen.scope)
}

/// A scope.
#[derive(Debug)]
pub struct Scope<'a> {
    /// The node which generates this scope.
    pub node: &'a dyn ScopedNode<'a>,
    /// The node which generates the parent scope, if any.
    pub parent: Option<&'a dyn ScopedNode<'a>>,
    /// The definitions in this scope.
    pub defs: HashMap<Name, Def<'a>>,
    /// The wildcard imports in this scope.
    pub wildcard_imports: Vec<&'a ast::ImportItem<'a>>,
    /// The subscopes.
    pub subscopes: Vec<&'a dyn ScopedNode<'a>>,
}

/// A definition in a scope.
#[derive(Debug, Clone, Copy)]
pub struct Def<'a> {
    /// The node which defines the name.
    pub node: DefNode<'a>,
    /// The name of the definition.
    pub name: Spanned<Name>,
    /// Where the definition is visible.
    pub vis: DefVis,
    /// Whether the definition may override a previous one.
    pub may_override: bool,
    /// Whether the definitions is only visible to things that come after it.
    pub ordered: bool,
}

bitflags::bitflags! {
    /// Visibility of a definition.
    pub struct DefVis: u8 {
        /// Whether the definition is visible to local resolution, e.g. `foo`.
        const LOCAL = 1 << 0;
        /// Whether the definition is accessible in a hierarchical name, e.g.
        /// `parent.foo`.
        const HIERARCHICAL = 1 << 1;
        /// Whether the definition is accessible during namespace resolution,
        /// e.g. `parent::foo`.
        const NAMESPACE = 1 << 2;
        /// Whether the definitions is visible in the global scope. Definitions
        /// in a `SourceFile` will be re-exported into `Root` if they are marked
        /// as global.
        const GLOBAL = 1 << 3;
    }
}

/// A node that generates a definition.
#[derive(Debug, Clone, Copy)]
pub enum DefNode<'a> {
    /// Any AST node.
    Ast(&'a dyn ast::AnyNode<'a>),
    /// An internal port of a module.
    IntPort(&'a port_list::IntPort<'a>),
}

impl<'a> std::fmt::Display for DefNode<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match *self {
            DefNode::Ast(node) => std::fmt::Display::fmt(node, f),
            DefNode::IntPort(node) => std::fmt::Display::fmt(node.ast, f),
        }
    }
}

impl<'a> ast::AnyNode<'a> for DefNode<'a> {
    fn id(&self) -> moore_common::NodeId {
        match *self {
            DefNode::Ast(node) => node.id(),
            DefNode::IntPort(node) => node.id,
        }
    }

    fn span(&self) -> moore_common::source::Span {
        match *self {
            DefNode::Ast(node) => node.span(),
            DefNode::IntPort(node) => node.span,
        }
    }

    fn order(&self) -> usize {
        match *self {
            DefNode::Ast(node) => node.order(),
            DefNode::IntPort(node) => node.ast.order(),
        }
    }
}

impl<'a> ast::AnyNodeData for DefNode<'a> {
    fn fmt_indefinite(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match *self {
            DefNode::Ast(node) => node.fmt_indefinite(f),
            DefNode::IntPort(node) => node.ast.fmt_indefinite(f),
        }
    }
}

impl<'a> ast::BasicNode<'a> for DefNode<'a> {
    fn type_name(&self) -> &'static str {
        match self {
            DefNode::Ast(node) => node.type_name(),
            DefNode::IntPort(node) => node.ast.type_name(),
        }
    }

    fn as_all(&'a self) -> syntax::ast::AllNode<'a> {
        match self {
            DefNode::Ast(node) => node.as_all(),
            DefNode::IntPort(node) => node.ast.as_all(),
        }
    }

    fn as_any(&'a self) -> &'a (dyn syntax::ast::AnyNode<'a> + 'a) {
        match self {
            DefNode::Ast(node) => node.as_any(),
            DefNode::IntPort(node) => node.ast.as_any(),
        }
    }
}

// TODO: The following visitor business should not be necessary just to get some
// struct to act like a fundamental node.
impl<'a> ast::AcceptVisitor<'a> for DefNode<'a> {
    fn accept(&'a self, _: &mut dyn syntax::ast::Visitor<'a>) {
        panic!("accept() called on non-AST node {:?}", self);
    }
}
impl<'a> ast::ForEachNode<'a> for DefNode<'a> {}
impl<'a> ast::ForEachChild<'a> for DefNode<'a> {
    fn for_each_child(&'a self, _: &mut dyn std::ops::FnMut(&'a dyn ast::AnyNode<'a>)) {
        panic!("for_each_child() called on non-AST node {:?}", self);
    }
}

/// A visitor that gathers the contents of a scope from the AST.
struct ScopeGenerator<'a, 'c, C> {
    /// The context.
    cx: &'c C,
    /// The scope being assembled.
    scope: Scope<'a>,
}

impl<'a, 'c, C: Context<'a>> ScopeGenerator<'a, 'c, C> {
    /// Create a new scope generator.
    pub fn new(cx: &'c C, scope: Scope<'a>) -> Self {
        ScopeGenerator { cx, scope }
    }

    /// Register a subscope.
    pub fn add_subscope(&mut self, node: &'a dyn ScopedNode<'a>) {
        trace!(" - Adding subscope for {:?}", node);
        self.scope.subscopes.push(node);
    }

    /// Register a wildcard import.
    pub fn add_wildcard_import(&mut self, node: &'a ast::ImportItem<'a>) {
        trace!(" - Adding wildcard import {:?}", node);
        self.scope.wildcard_imports.push(node);
    }

    /// Register a definition.
    pub fn add_def(&mut self, mut def: Def<'a>) {
        trace!(" - Adding definition {:?}", def);

        // Check that the definition does not collide with a previous one.
        if let Some(existing) = self.scope.defs.get(&def.name.value) {
            match existing.node {
                // Do not redefine ports.
                DefNode::IntPort(_) => return,
                // Handle being allowed to override forward declarations
                DefNode::Ast(node) => {
                    if let ast::AllNode::Typedef(ast) = node.as_all() {
                        if let ast::ForwardType { kind: _ } = ast.ty.kind.data {
                            def.may_override = true;
                        }
                    }
                }
            };

            // We can also have multiple forward declarations of the same name, must
            // ignore all but the first one here. This also correctly handles the case
            // where a "forward" declaration actually comes after the definition, which
            // is apparently not an error in svlog.
            if let DefNode::Ast(node) = def.node {
                if let ast::AllNode::Typedef(ast) = node.as_all() {
                    if let ast::ForwardType { kind: _ } = ast.ty.kind.data {
                        return;
                    }
                }
            }

            if !def.may_override {
                let d = DiagBuilder2::error(format!("`{}` is defined multiple times", def.name))
                    .span(def.name.span)
                    .add_note(format!("Previous definition of `{}` was here:", def.name))
                    .span(existing.name.span);
                self.cx.emit(d);
                return;
            }
        }

        // Store the definition.
        self.scope.defs.insert(def.name.value, def);
    }
}

impl<'a, C: Context<'a>> ast::Visitor<'a> for ScopeGenerator<'a, '_, C> {
    // We return `false` in the pre-visit functions when the visited node
    // generates a subscope, to avoid gobbling up its local definitions.

    fn pre_visit_root(&mut self, node: &'a ast::Root<'a>) -> bool {
        self.add_subscope(node);
        false
    }

    fn pre_visit_source_file(&mut self, node: &'a ast::SourceFile<'a>) -> bool {
        self.add_subscope(node);
        false
    }

    fn pre_visit_module(&mut self, node: &'a ast::Module<'a>) -> bool {
        self.add_subscope(node);
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::GLOBAL,
            may_override: true,
            ordered: false,
        });
        false
    }

    fn pre_visit_interface(&mut self, node: &'a ast::Interface<'a>) -> bool {
        self.add_subscope(node);
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::GLOBAL,
            may_override: true,
            ordered: false,
        });
        false
    }

    fn pre_visit_modport_name(&mut self, node: &'a ast::ModportName<'a>) -> bool {
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: false,
        });
        false
    }

    fn pre_visit_package(&mut self, node: &'a ast::Package<'a>) -> bool {
        self.add_subscope(node);
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::NAMESPACE | DefVis::GLOBAL,
            may_override: false,
            ordered: false,
        });
        false
    }

    fn pre_visit_import_item(&mut self, node: &'a ast::ImportItem<'a>) -> bool {
        if let Some(name) = node.name {
            self.add_def(Def {
                node: DefNode::Ast(node),
                name,
                vis: DefVis::LOCAL,
                may_override: false,
                ordered: true,
            });
        } else {
            self.add_wildcard_import(node);
        }
        true
    }

    fn pre_visit_var_decl_name(&mut self, node: &'a ast::VarDeclName<'a>) -> bool {
        // Don't register definitions for struct members.
        if node
            .get_parent()
            .and_then(|p| p.as_all().get_struct_member())
            .is_some()
        {
            return true;
        }
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: Spanned::new(node.name, node.name_span),
            vis: DefVis::LOCAL | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: true,
        });
        true
    }

    fn pre_visit_param_type_decl(&mut self, node: &'a ast::ParamTypeDecl<'a>) -> bool {
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::NAMESPACE | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: true,
        });
        true
    }

    fn pre_visit_param_value_decl(&mut self, node: &'a ast::ParamValueDecl<'a>) -> bool {
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::NAMESPACE | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: true,
        });
        true
    }

    fn pre_visit_genvar_decl(&mut self, node: &'a ast::GenvarDecl<'a>) -> bool {
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: true,
        });
        true
    }

    fn pre_visit_enum_name(&mut self, node: &'a ast::EnumName<'a>) -> bool {
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::NAMESPACE | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: true,
        });
        true
    }

    fn pre_visit_typedef(&mut self, node: &'a ast::Typedef<'a>) -> bool {
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::NAMESPACE | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: true,
        });
        true
    }

    fn pre_visit_procedure(&mut self, node: &'a ast::Procedure<'a>) -> bool {
        self.add_subscope(node);
        false
    }

    fn pre_visit_class_decl(&mut self, node: &'a ast::ClassDecl<'a>) -> bool {
        self.add_subscope(node);
        // self.add_def(Def {
        //     node: DefNode::Ast(node),
        //     name: node.name,
        //     vis: DefVis::LOCAL | DefVis::NAMESPACE,
        //     may_override: false,
        //     ordered: true,
        // });
        false
    }

    fn pre_visit_subroutine_decl(&mut self, node: &'a ast::SubroutineDecl<'a>) -> bool {
        self.add_subscope(node);
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.prototype.name,
            vis: DefVis::LOCAL | DefVis::NAMESPACE | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: false,
        });
        false
    }

    fn pre_visit_subroutine_port(&mut self, node: &'a ast::SubroutinePort<'a>) -> bool {
        // TODO(fschuiki): This one is nasty. The unique case is simple, because
        // we know that the name we see is *actually* the name of the port. In
        // the ambiguous case however, we have to first find out which one of
        // the possibilities is correct (i.e. the type-only or name-only one),
        // before deciding whether to add a definition here. If we don't do
        // this, we might shadow a legitimate type name with the port.
        if let ast::Ambiguous::Unique((ref _ty, Some(ref name))) = node.ty_name {
            self.add_def(Def {
                node: DefNode::Ast(node),
                name: name.name,
                vis: DefVis::LOCAL,
                may_override: false,
                ordered: true,
            });
        }
        true
    }

    fn pre_visit_inst_name(&mut self, node: &'a ast::InstName<'a>) -> bool {
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL | DefVis::HIERARCHICAL,
            may_override: false,
            ordered: false,
        });
        true
    }

    fn pre_visit_generate_for(&mut self, node: &'a ast::GenerateFor<'a>) -> bool {
        self.add_subscope(node);
        false
    }

    fn pre_visit_generate_if(&mut self, node: &'a ast::GenerateIf<'a>) -> bool {
        self.add_subscope(node);
        false
    }

    fn pre_visit_generate_case(&mut self, node: &'a ast::GenerateCase<'a>) -> bool {
        self.add_subscope(node);
        false
    }

    fn pre_visit_generate_block(&mut self, node: &'a ast::GenerateBlock<'a>) -> bool {
        self.add_subscope(node);
        if let Some(name) = node.label {
            self.add_def(Def {
                node: DefNode::Ast(node),
                name,
                vis: DefVis::LOCAL | DefVis::HIERARCHICAL,
                may_override: false,
                ordered: false,
            });
        }
        false
    }

    fn pre_visit_stmt(&mut self, node: &'a ast::Stmt<'a>) -> bool {
        // Do not traverse into statements that generate their own scope.
        match node.kind {
            ast::SequentialBlock(..)
            | ast::ParallelBlock(..)
            | ast::IfStmt { .. }
            | ast::CaseStmt { .. }
            | ast::ForeverStmt(..)
            | ast::RepeatStmt(..)
            | ast::WhileStmt(..)
            | ast::DoStmt(..)
            | ast::ForStmt(..)
            | ast::ForeachStmt(..) => {
                self.add_subscope(node);
                false
            }
            _ => true,
        }
    }

    fn pre_visit_foreach_index(&mut self, node: &'a ast::ForeachIndex<'a>) -> bool {
        self.add_def(Def {
            node: DefNode::Ast(node),
            name: node.name,
            vis: DefVis::LOCAL,
            may_override: false,
            ordered: true,
        });
        true
    }

    fn pre_visit_dpi_decl(&mut self, node: &'a ast::DpiDecl<'a>) -> bool {
        match node.data {
            ast::DpiDeclData::Import { ref prototype, .. } => {
                self.add_def(Def {
                    node: DefNode::Ast(node),
                    name: prototype.name,
                    vis: DefVis::LOCAL | DefVis::NAMESPACE,
                    may_override: false,
                    ordered: true,
                });
            }
            _ => (),
        }
        false
    }
}

/// Determine the location of a node within its enclosing scope.
#[moore_derive::query]
pub(crate) fn scope_location<'a>(
    cx: &impl Context<'a>,
    node: &'a dyn ast::AnyNode<'a>,
) -> ScopeLocation<'a> {
    trace!("Finding scope location of {:?}", node);

    // Keep the lexical order of the initiating node around.
    let order = node.order();

    // Starting at the current node, check if it generates a scope, and if not,
    // advance to its parent.
    let mut next: Option<&dyn ast::AnyNode> = node.get_parent();
    while let Some(node) = next {
        if let Some(scoped) = node.as_all().get_scoped_node() {
            trace!(" - Found {:?}", node);
            return ScopeLocation {
                scope: scoped,
                order,
            };
        } else {
            trace!(" - Upwards to {:?}", node);
            next = node.get_parent();
        }
    }

    // We should never arrive here, since the root node always generates a
    // scope.
    bug_span!(
        node.span(),
        cx,
        "arrived at root node {:?}, which must generate a scope",
        node
    );
}

/// A location of a node within its enclosing scope.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub struct ScopeLocation<'a> {
    /// The node which generates the enclosing scope.
    pub scope: &'a dyn ScopedNode<'a>,
    /// The lexical order within that scope.
    pub order: usize,
}

/// Resolve a local name in a scope.
///
/// This traverses up the scope tree until a definition with visibility `LOCAL`
/// is found. Returns `None` if no such name exists.
#[moore_derive::query]
pub(crate) fn resolve_local<'a>(
    cx: &impl Context<'a>,
    name: Name,
    at: ScopeLocation<'a>,
    skip_imports: bool,
) -> Result<Option<&'a Def<'a>>> {
    debug!("Resolving `{}` locally at {:?}", name, at);
    let scope = cx.generated_scope(at.scope);
    let mut next = Some(scope);
    while let Some(scope) = next {
        next = scope.parent.map(|p| cx.generated_scope(p));
        trace!(" - Looking in scope {:?}", scope.node);

        // Try to find a matching definition in this scope.
        if let Some(def) = scope.defs.get(&name) {
            // Check if it is visible to local name resolution.
            let vis_ok = def.vis.contains(DefVis::LOCAL);

            // If the definition requires def-before-use, check that it was defined
            // before the location we are trying to use it.
            let order_ok = !def.ordered || def.node.order() < at.order;

            // Return this definition if it matches.
            if vis_ok && order_ok {
                // In case what we've found is an import like `import foo::A`,
                // resolve `A` in `foo` now.
                let def = if let DefNode::Ast(node) = def.node {
                    if let Some(import) = node.as_all().get_import_item() {
                        trace!(" - Following {:?}", import);
                        let inside = cx.resolve_imported_scope(import)?;
                        let binding =
                            cx.resolve_namespace_or_error(import.name.unwrap(), inside)?;
                        binding
                    } else {
                        def
                    }
                } else {
                    def
                };

                debug!(" - Found {:?}", def);
                return Ok(Some(def));
            }
        }

        // Check the wildcard imports for any luck.
        if skip_imports {
            continue;
        }
        for &import in scope.wildcard_imports.iter().rev() {
            if import.order() > at.order {
                continue;
            }
            let inside = cx.resolve_imported_scope(import)?;
            let def = cx.resolve_namespace(name, inside);
            if def.is_some() {
                return Ok(def);
            }
        }
    }
    Ok(None)
}

/// Resolve a local name in a scope or emit an error.
///
/// Calls `resolve_local`. Either returns `Ok` if a node was found, or `Err`
/// after emitting a diagnostic error message.
#[moore_derive::query]
pub(crate) fn resolve_local_or_error<'a>(
    cx: &impl Context<'a>,
    name: Spanned<Name>,
    at: ScopeLocation<'a>,
    skip_imports: bool,
) -> Result<&'a Def<'a>> {
    match cx.resolve_local(name.value, at, skip_imports)? {
        Some(def) => {
            if cx.sess().has_verbosity(Verbosity::NAMES) {
                let d = DiagBuilder2::note("name resolution")
                    .span(name.span)
                    .add_note(format!("Resolved `{}` to this {}:", name, def.node))
                    .span(def.node.span());
                cx.emit(d);
            }
            Ok(def)
        }
        None => {
            cx.emit(DiagBuilder2::error(format!("`{}` not found", name.value)).span(name.span));
            Err(())
        }
    }
}

/// Resolve a name in a scope as a namespace lookup.
///
/// This checks if the scope contains a definition with visibility
/// `NAMESPACE`. Returns `None` if no such name exists.
#[moore_derive::query]
pub(crate) fn resolve_namespace<'a>(
    cx: &impl Context<'a>,
    name: Name,
    inside: &'a dyn ScopedNode<'a>,
) -> Option<&'a Def<'a>> {
    debug!("Resolving `{}` in namespace {:?}", name, inside);
    let scope = cx.generated_scope(inside);
    match scope.defs.get(&name) {
        Some(def) if def.vis.contains(DefVis::NAMESPACE) => {
            debug!(" - Found {:?}", def);
            Some(def)
        }
        _ => None,
    }
}

/// Resolve a name in a scope as a namespace lookup or emit an error.
///
/// Calls `resolve_namespace`. Either returns `Ok` if a node was found, or `Err`
/// after emitting a diagnostic error message.
#[moore_derive::query]
pub(crate) fn resolve_namespace_or_error<'a>(
    cx: &impl Context<'a>,
    name: Spanned<Name>,
    inside: &'a dyn ScopedNode<'a>,
) -> Result<&'a Def<'a>> {
    match cx.resolve_namespace(name.value, inside) {
        Some(def) => {
            if cx.sess().has_verbosity(Verbosity::NAMES) {
                let d = DiagBuilder2::note("name resolution")
                    .span(name.span)
                    .add_note(format!("Resolved `{}` to this {}:", name, def.node))
                    .span(def.node.span());
                cx.emit(d);
            }
            Ok(def)
        }
        None => {
            cx.emit(
                DiagBuilder2::error(format!("`{}` not found in {}", name.value, inside))
                    .span(name.span)
                    .add_note(format!("{} was defined here:", inside))
                    .span(inside.human_span()),
            );
            Err(())
        }
    }
}

/// Resolve a name in a scope as a hierarchical lookup.
///
/// This checks if the scope contains a definition with visibility
/// `HIERARCHICAL`. Returns `None` if no such name exists.
#[moore_derive::query]
pub(crate) fn resolve_hierarchical<'a>(
    cx: &impl Context<'a>,
    name: Name,
    inside: &'a dyn ScopedNode<'a>,
) -> Option<&'a Def<'a>> {
    debug!("Resolving `{}` hierarchically in {:?}", name, inside);
    let scope = cx.generated_scope(inside);
    match scope.defs.get(&name) {
        Some(def) if def.vis.contains(DefVis::HIERARCHICAL) => {
            debug!(" - Found {:?}", def);
            Some(def)
        }
        _ => None,
    }
}

/// Resolve a name in a scope as a hierarchical lookup or emit an error.
///
/// Calls `resolve_hierarchical`. Either returns `Ok` if a node was found, or
/// `Err` after emitting a diagnostic error message.
#[moore_derive::query]
pub(crate) fn resolve_hierarchical_or_error<'a>(
    cx: &impl Context<'a>,
    name: Spanned<Name>,
    inside: &'a dyn ScopedNode<'a>,
) -> Result<&'a Def<'a>> {
    match cx.resolve_hierarchical(name.value, inside) {
        Some(def) => {
            if cx.sess().has_verbosity(Verbosity::NAMES) {
                let d = DiagBuilder2::note("name resolution")
                    .span(name.span)
                    .add_note(format!("Resolved `{}` to this {}:", name, def.node))
                    .span(def.node.span());
                cx.emit(d);
            }
            Ok(def)
        }
        None => {
            cx.emit(
                DiagBuilder2::error(format!("`{}` not found in {}", name.value, inside))
                    .span(name.span)
                    .add_note(format!("{} was defined here:", inside))
                    .span(inside.human_span()),
            );
            Err(())
        }
    }
}

/// Resolve an import to the scope it imports.
///
/// This function emits a diagnostic if the target of the import has no scope.
/// Being a query, this ensures that the error is only produced once.
#[moore_derive::query]
pub(crate) fn resolve_imported_scope<'a>(
    cx: &impl Context<'a>,
    node: &'a ast::ImportItem<'a>,
) -> Result<&'a dyn ScopedNode<'a>> {
    // Resolve the imported name, e.g. the `foo` in `import foo::*`.
    let at = cx.scope_location(node);
    let inside = cx.resolve_local_or_error(node.pkg, at, true)?;

    // Ensure that what we have found is something we can actually perform a
    // namespace lookup into.
    let inside = match inside.node {
        DefNode::Ast(node) => Some(node),
        _ => None,
    };
    let inside = inside.and_then(|x| x.as_all().get_scoped_node());
    match inside {
        Some(x) => Ok(x),
        None => {
            cx.emit(
                DiagBuilder2::error(format!("name `{}` does not refer to a package", node.pkg))
                    .span(node.pkg.span),
            );
            Err(())
        }
    }
}

/// Recursively ensures that all scopes have been constructed and potential
/// diagnostics emitted.
///
/// This function helps in triggering naming conflicts at a defined point in the
/// compilation.
pub(crate) fn materialize_scope<'a>(cx: &impl Context<'a>, node: &'a dyn ScopedNode<'a>) {
    debug!("Materializing scope {:?}", node);
    let scope = cx.generated_scope(node);
    for &subscope in &scope.subscopes {
        materialize_scope(cx, subscope);
    }
}

/// Recursively resolves names throughout the AST.
///
/// Returns `true` if all names resolved successfully, `false` otherwise. This
/// function helps in triggering name resolution errors at a defined point in
/// the compilation.
#[moore_derive::query]
pub(crate) fn nameck<'a>(cx: &impl Context<'a>, node: &'a dyn ast::AnyNode<'a>) -> bool {
    debug!("Checking name resolution on {:?}", node);
    let mut rv = ResolutionVisitor::new(cx);
    node.accept(&mut rv);
    !rv.failed
}

/// A visitor that emits diagnostics for every resolved named.
pub(crate) struct ResolutionVisitor<'cx, C> {
    pub cx: &'cx C,
    pub failed: bool,
}

impl<'cx, C> ResolutionVisitor<'cx, C> {
    /// Create a new name resolution visitor.
    pub fn new(cx: &'cx C) -> Self {
        ResolutionVisitor { cx, failed: false }
    }
}

impl<'a, 'cx, C> ast::Visitor<'a> for ResolutionVisitor<'cx, C>
where
    C: Context<'a>,
    'a: 'cx,
{
    fn pre_visit_expr(&mut self, node: &'a ast::Expr<'a>) -> bool {
        // Don't resolve the left-hand side of named pattern fields,
        // since these refer to field names.
        if let Some(patfield) = node
            .get_parent()
            .and_then(|p| p.as_all().get_pattern_field())
        {
            match patfield.data {
                ast::PatternFieldData::Member(ref name_expr, ..) if name_expr.as_ref() == node => {
                    return false;
                }
                _ => (),
            }
        }

        // Don't resolve the expression in implicit and explicit ports.
        // These are meant to be analyzed in more detail by the port
        // list ananlysis query.
        if let Some(port) = node.get_parent().and_then(|p| p.as_all().get_port()) {
            debug!("Checking {:?} in port {:?}", node, port);
            match port.data {
                ast::PortData::Explicit { .. } | ast::PortData::Implicit(..) => return false,
                _ => (),
            }
        }

        match node.data {
            ast::IdentExpr(ident) => {
                self.failed |= self
                    .cx
                    .resolve_local_or_error(ident, self.cx.scope_location(node), false)
                    .is_err();
                false
            }
            _ => true,
        }
    }

    fn pre_visit_type(&mut self, node: &'a ast::Type<'a>) -> bool {
        match node.kind.data {
            ast::NamedType(ident) => {
                self.failed |= self
                    .cx
                    .resolve_local_or_error(ident, self.cx.scope_location(node), false)
                    .is_err();
                false
            }
            _ => true,
        }
    }

    /// Override for `SubroutinePort`s in order to resolve ambiguity.
    // TODO(fschuik): This functionality should go into a `rst::Visitor`.
    fn pre_visit_subroutine_port(&mut self, node: &'a ast::SubroutinePort<'a>) -> bool {
        use ast::WalkVisitor;
        node.dir.walk(self);
        node.var.walk(self);
        self.cx
            .resolve_subroutine_port_ty_name(Ref(node))
            .walk(self);
        false
    }
}

/// Any AST node that can be instantiated.
#[derive(Debug, Clone, Copy)]
pub enum InstTarget<'a> {
    /// A module instance.
    Module(&'a ast::Module<'a>),
    /// A interface instance.
    Interface(&'a ast::Interface<'a>),
}

impl<'a> InstTarget<'a> {
    /// Get the instantiated node as a `AnyNode`.
    pub fn as_any(&self) -> &'a dyn ast::AnyNode<'a> {
        match *self {
            Self::Module(x) => x,
            Self::Interface(x) => x,
        }
    }
}

/// Resolve the target of an instantiation.
#[moore_derive::query]
pub(crate) fn resolve_inst_target<'a>(
    cx: &impl Context<'a>,
    inst: &'a ast::Inst<'a>,
) -> Result<InstTarget<'a>> {
    // Resolve the name of the instantiated module.
    let loc = cx.scope_location(inst);
    let def = cx.resolve_local_or_error(inst.target, loc, false)?;
    trace!("Resolved instance `{}` to {:?}", inst.target, def);

    // Check what exactly we are instantiating.
    let target = match def.node {
        DefNode::Ast(ast) => match ast.as_all() {
            ast::AllNode::Module(x) => Some(InstTarget::Module(x)),
            ast::AllNode::Interface(x) => Some(InstTarget::Interface(x)),
            _ => None,
        },
        _ => None,
    };
    match target {
        Some(x) => Ok(x),
        None => {
            cx.emit(
                DiagBuilder2::error(format!("`{}` is not a module or interface", inst.target))
                    .span(inst.target.span)
                    .add_note(format!("{} was declared here:", def.node))
                    .span(def.node.span()),
            );
            Err(())
        }
    }
}