iecst

⚠️ DEPRECATED: This crate is deprecated in favor of iec61131, which provides complete IEC 61131-3 support for all 5 programming languages (ST, IL, LD, FBD, SFC) based on the official specification. New projects should use iec61131 instead.

IEC 61131-3 Structured Text parser for Rust.

Overview

iecst is a parser for IEC 61131-3 Structured Text (ST), the high-level programming language used in PLC (Programmable Logic Controller) programming.

Features

• Full ST syntax support - expressions, statements, POUs, declarations
• Minimal dependencies (winnow for parsing)
• Detailed error reporting with source locations
• AST output for further analysis or transformation
• Control Flow Graph (CFG) - build CFGs from ST code for complexity analysis
• Cyclomatic complexity - calculate code complexity metrics
• Nesting depth analysis - detect deeply nested control structures
• Basic static analysis - type checking, unused variables, diagnostics
• Security features - DoS protection with configurable resource limits

Installation

Add to your Cargo.toml:

[dependencies]
iecst = "0.5"

Quick Start

use iecst::{parse_statement, parse_expression};

// Parse a statement
let stmt = parse_statement("x := 1 + 2;").unwrap();

// Parse an expression
let expr = parse_expression("a AND b OR c").unwrap();

Security

For untrusted input, use security limits to prevent DoS attacks:

use iecst::{Parser, security::ParserLimits};

// Use strict limits for untrusted input
let limits = ParserLimits::strict();
let parser = Parser::new_with_limits(source, limits)?;

// Available profiles:
// - ParserLimits::strict()    - For untrusted input (10 MB, 64 levels)
// - ParserLimits::balanced()  - For typical files (100 MB, 256 levels)
// - ParserLimits::relaxed()   - For trusted files (500 MB, 512 levels)

Supported Constructs

Expressions

• Literals: integers, reals, strings, booleans, time literals
• Identifiers and qualified names
• Binary operators: +, -, *, /, MOD, **, AND, OR, XOR, comparisons
• Unary operators: -, NOT
• Function calls: SIN(x), MAX(a, b)
• Array indexing: arr[i], arr[i, j]
• Member access: struct.field

Statements

• Assignment: x := expr;
• IF/THEN/ELSIF/ELSE/END_IF
• CASE/OF/ELSE/END_CASE
• FOR/TO/BY/DO/END_FOR
• WHILE/DO/END_WHILE
• REPEAT/UNTIL/END_REPEAT
• EXIT, RETURN, CONTINUE

Program Organization Units (POUs)

• PROGRAM/END_PROGRAM
• FUNCTION/END_FUNCTION
• FUNCTION_BLOCK/END_FUNCTION_BLOCK

Declarations

• VAR/VAR_INPUT/VAR_OUTPUT/VAR_IN_OUT/VAR_TEMP/VAR_GLOBAL
• TYPE/END_TYPE (structures, enums, arrays, subranges)

Example: Parsing a Function Block

use iecst::parse_pou;

let code = r#"
FUNCTION_BLOCK Counter
    VAR_INPUT
        Reset : BOOL;
    END_VAR
    VAR_OUTPUT
        Count : INT;
    END_VAR
    VAR
        _count : INT := 0;
    END_VAR
    
    IF Reset THEN
        _count := 0;
    ELSE
        _count := _count + 1;
    END_IF;
    
    Count := _count;
END_FUNCTION_BLOCK
"#;

let pou = parse_pou(code).unwrap();
println!("Parsed: {:?}", pou.name);

Static Analysis

use iecst::{parse_pou, analyze_pou};

let code = "FUNCTION Test : INT VAR x : INT; END_VAR x := 1; Test := x; END_FUNCTION";
let pou = parse_pou(code).unwrap();
let diagnostics = analyze_pou(&pou);

for diag in diagnostics {
    println!("[{}] {}", diag.severity, diag.message);
}

Control Flow Graph

Build a CFG from ST statements to analyze control flow and calculate complexity:

use iecst::{parse_statements, CfgBuilder};

let code = r#"
    IF x > 0 THEN
        y := 1;
    ELSIF x < 0 THEN
        y := -1;
    ELSE
        y := 0;
    END_IF;
"#;

let stmts = parse_statements(code).unwrap();
let cfg = CfgBuilder::new().build(&stmts);

// Calculate cyclomatic complexity
let complexity = cfg.cyclomatic_complexity();
println!("Cyclomatic complexity: {}", complexity); // Output: 3

// Export to Graphviz DOT format for visualization
let dot = cfg.to_dot();
println!("{}", dot);

Nesting Depth Analysis

Detect deeply nested control structures:

use iecst::{parse_statements, max_nesting_depth};

let code = r#"
    IF a THEN
        FOR i := 1 TO 10 DO
            WHILE b DO
                x := x + 1;
            END_WHILE;
        END_FOR;
    END_IF;
"#;

let stmts = parse_statements(code).unwrap();
let depth = max_nesting_depth(&stmts);
println!("Max nesting depth: {}", depth); // Output: 3

CFG Features

• Cyclomatic complexity - cfg.cyclomatic_complexity() using edge formula (E - N + 2)
• Decision-based complexity - cfg.cyclomatic_complexity_decisions() counting branch points
• Unreachable code detection - cfg.unreachable_nodes() finds dead code
• Path analysis - cfg.has_path(from, to) checks reachability
• DOT export - cfg.to_dot() for Graphviz visualization