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* Division By Zero Analyzer
* Detects division and modulo by zero at compile time (ADR-051)
*
* Implemented Phases:
* ✓ Phase 1: Literal zero detection (10 / 0, 10 % 0)
* ✓ Phase 3: Const zero detection (const u32 ZERO <- 0; x / ZERO)
*
* Future Enhancement (Phase 3+):
* - Const expression evaluation (const u32 VALUE <- 5 - 5; x / VALUE)
*/
import { ParseTreeWalker } from "antlr4ng";
import { CNextListener } from "../parser/grammar/CNextListener";
import * as Parser from "../parser/grammar/CNextParser";
import IDivisionByZeroError from "./types/IDivisionByZeroError";
import LiteralUtils from "../../../utils/LiteralUtils";
import ExpressionUtils from "../../../utils/ExpressionUtils";
import ParserUtils from "../../../utils/ParserUtils";
/**
* First pass: Collect const declarations that are zero
*/
class ConstZeroCollector extends CNextListener {
private readonly constZeros: Set<string> = new Set();
public getConstZeros(): Set<string> {
return this.constZeros;
}
/**
* Track const declarations
* variableDeclaration: atomicModifier? volatileModifier? constModifier? ...
*/
override enterVariableDeclaration = (
ctx: Parser.VariableDeclarationContext,
): void => {
// Only process const declarations
if (!ctx.constModifier()) {
return;
}
const identifier = ctx.IDENTIFIER();
Iif (!identifier) {
return;
}
const name = identifier.getText();
const expr = ctx.expression();
Iif (!expr) {
return;
}
// Check if the expression is a literal zero
const literal = ExpressionUtils.extractLiteral(expr);
if (literal && LiteralUtils.isZero(literal)) {
this.constZeros.add(name);
}
};
}
/**
* Second pass: Detect division by zero (including const identifiers)
*/
class DivisionByZeroListener extends CNextListener {
private readonly analyzer: DivisionByZeroAnalyzer;
// eslint-disable-next-line @typescript-eslint/lines-between-class-members
private readonly constZeros: Set<string>;
constructor(analyzer: DivisionByZeroAnalyzer, constZeros: Set<string>) {
super();
this.analyzer = analyzer;
this.constZeros = constZeros;
}
/**
* Check multiplicative expressions for division/modulo by zero
* multiplicativeExpression: unaryExpression (('*' | '/' | '%') unaryExpression)*
*/
override enterMultiplicativeExpression = (
ctx: Parser.MultiplicativeExpressionContext,
): void => {
// Get all unary expressions
const operands = ctx.unaryExpression();
if (operands.length < 2) {
return; // No operator, just a single operand
}
// Check each operator and its right operand
for (let i = 0; i < operands.length - 1; i++) {
const operatorToken = ctx.getChild(i * 2 + 1); // Operators are at odd indices
Iif (!operatorToken) continue;
const operator = operatorToken.getText();
if (operator !== "/" && operator !== "%") {
continue; // Only check division and modulo
}
const rightOperand = operands[i + 1];
const { line, column } = ParserUtils.getPosition(rightOperand);
// Check if right operand is zero
if (this.isZero(rightOperand)) {
this.analyzer.addError(operator, line, column);
}
}
};
/**
* Check if a unary expression evaluates to zero
*/
private isZero(ctx: Parser.UnaryExpressionContext): boolean {
// Get the postfix expression
const postfixExpr = ctx.postfixExpression();
if (!postfixExpr) {
return false;
}
// Get the primary expression
const primaryExpr = postfixExpr.primaryExpression();
Iif (!primaryExpr) {
return false;
}
// Check if it's a literal
const literal = primaryExpr.literal();
if (literal) {
return LiteralUtils.isZero(literal);
}
// Check if it's a const identifier that evaluates to zero
const identifier = primaryExpr.IDENTIFIER();
if (identifier) {
const name = identifier.getText();
return this.constZeros.has(name);
}
return false;
}
}
/**
* Analyzer that detects division by zero
*/
class DivisionByZeroAnalyzer {
private errors: IDivisionByZeroError[] = [];
/**
* Analyze the parse tree for division by zero
* Two-pass analysis:
* 1. Collect const declarations that are zero
* 2. Detect division/modulo by literal zero or const zero
*/
public analyze(tree: Parser.ProgramContext): IDivisionByZeroError[] {
this.errors = [];
// First pass: collect const zeros
const collector = new ConstZeroCollector();
ParseTreeWalker.DEFAULT.walk(collector, tree);
const constZeros = collector.getConstZeros();
// Second pass: detect division by zero
const listener = new DivisionByZeroListener(this, constZeros);
ParseTreeWalker.DEFAULT.walk(listener, tree);
return this.errors;
}
/**
* Add a division by zero error
*/
public addError(operator: string, line: number, column: number): void {
const isDivision = operator === "/";
const code = isDivision ? "E0800" : "E0802";
const opName = isDivision ? "Division" : "Modulo";
this.errors.push({
code,
operator,
line,
column,
message: `${opName} by zero`,
helpText: isDivision
? "Consider using safe_div(output, numerator, divisor, defaultValue) for runtime safety"
: "Consider using safe_mod(output, numerator, divisor, defaultValue) for runtime safety",
});
}
/**
* Get all detected errors
*/
public getErrors(): IDivisionByZeroError[] {
return this.errors;
}
}
export default DivisionByZeroAnalyzer;
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