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* Signed Shift Analyzer
* Detects shift operators used with signed integer types at compile time
*
* MISRA C:2012 Rule 10.1: Operands shall not be of an inappropriate essential type
* - Left-shifting negative signed values is undefined behavior in C
* - Right-shifting negative signed values is implementation-defined in C
*
* C-Next rejects all shift operations on signed types (i8, i16, i32, i64) at
* compile time to ensure defined, portable behavior.
*
* Two-pass analysis:
* 1. Collect variable declarations with their types
* 2. Detect shift operations with signed operands
*/
import { ParseTreeWalker } from "antlr4ng";
import { CNextListener } from "../parser/grammar/CNextListener";
import * as Parser from "../parser/grammar/CNextParser";
import ISignedShiftError from "./types/ISignedShiftError";
import ParserUtils from "../../../utils/ParserUtils";
import TypeConstants from "../../../utils/constants/TypeConstants";
import ExpressionUtils from "../../../utils/ExpressionUtils";
import CodeGenState from "../../state/CodeGenState";
/**
* First pass: Collect variable declarations with their types
*/
class SignedVariableCollector extends CNextListener {
private readonly signedVars: Set<string> = new Set();
// Track all variable types (for resolving struct member chains)
private readonly varTypes: Map<string, string> = new Map();
public getSignedVars(): Set<string> {
return this.signedVars;
}
public getVarTypes(): Map<string, string> {
return this.varTypes;
}
/**
* Track a typed identifier - add to signedVars if signed, always track type
*/
private trackType(
typeCtx: Parser.TypeContext | null,
identifier: { getText(): string } | null,
): void {
Iif (!typeCtx || !identifier) return;
const typeName = typeCtx.getText();
const varName = identifier.getText();
// Always track the variable's type for member chain resolution
this.varTypes.set(varName, typeName);
// Also track in signedVars if it's a signed type
if (TypeConstants.SIGNED_TYPES.includes(typeName)) {
this.signedVars.add(varName);
}
}
/**
* Track variable declarations with signed types
*/
override enterVariableDeclaration = (
ctx: Parser.VariableDeclarationContext,
): void => {
this.trackType(ctx.type(), ctx.IDENTIFIER());
};
/**
* Track function parameters with signed types
*/
override enterParameter = (ctx: Parser.ParameterContext): void => {
this.trackType(ctx.type(), ctx.IDENTIFIER());
};
/**
* Track for-loop variable declarations with signed types
*/
override enterForVarDecl = (ctx: Parser.ForVarDeclContext): void => {
this.trackType(ctx.type(), ctx.IDENTIFIER());
};
}
/**
* Second pass: Detect shift operations with signed operands
*/
class SignedShiftListener extends CNextListener {
private readonly analyzer: SignedShiftAnalyzer;
// eslint-disable-next-line @typescript-eslint/lines-between-class-members
private readonly signedVars: Set<string>;
// eslint-disable-next-line @typescript-eslint/lines-between-class-members
private readonly varTypes: Map<string, string>;
constructor(
analyzer: SignedShiftAnalyzer,
signedVars: Set<string>,
varTypes: Map<string, string>,
) {
super();
this.analyzer = analyzer;
this.signedVars = signedVars;
this.varTypes = varTypes;
}
/**
* Check shift expressions for signed operands
* shiftExpression: additiveExpression (('<<' | '>>') additiveExpression)*
*/
override enterShiftExpression = (
ctx: Parser.ShiftExpressionContext,
): void => {
const operands = ctx.additiveExpression();
if (operands.length < 2) return;
// Check each operator between additive expressions
for (let i = 0; i < operands.length - 1; i++) {
const operatorToken = ctx.getChild(i * 2 + 1);
Iif (!operatorToken) continue;
const operator = operatorToken.getText();
Iif (operator !== "<<" && operator !== ">>") continue;
const leftOperand = operands[i];
// Check left operand (the value being shifted)
if (this.isSignedOperand(leftOperand)) {
const { line, column } = ParserUtils.getPosition(leftOperand);
this.analyzer.addError(line, column, operator);
}
}
};
/**
* Check compound shift-assign statements for signed targets
* assignmentStatement: assignmentTarget assignmentOperator expression ';'
* Issue #1008: <<<- and >><- must also be rejected on signed types
*
* Handles both simple identifiers (x <<<- 2) and member chains (s.x <<<- 2)
*/
override enterAssignmentStatement = (
ctx: Parser.AssignmentStatementContext,
): void => {
const opCtx = ctx.assignmentOperator();
Iif (!opCtx) return;
const isLeftShiftAssign = opCtx.LSHIFT_ASSIGN() !== null;
const isRightShiftAssign = opCtx.RSHIFT_ASSIGN() !== null;
if (!isLeftShiftAssign && !isRightShiftAssign) return;
const target = ctx.assignmentTarget();
Iif (!target) return;
// Get the base identifier from the assignment target
const identifier = target.IDENTIFIER();
Iif (!identifier) return;
const baseName = identifier.getText();
const postfixOps = target.postfixTargetOp();
// Check if the final target type is signed
if (this.isSignedTarget(baseName, postfixOps)) {
const operator = isLeftShiftAssign ? "<<<-" : ">><-";
const { line, column } = ParserUtils.getPosition(target);
this.analyzer.addError(line, column, operator);
}
};
/**
* Resolve the final type of an assignment target, handling member chains.
* Returns true if the final target is a signed type.
*
* Examples:
* - "x" with no postfix ops → check if x is signed
* - "s" with postfixOps [".x"] → check if s.x field is signed
* - "arr" with postfixOps ["[0]", ".field"] → check if field is signed
*/
private isSignedTarget(
baseName: string,
postfixOps: Parser.PostfixTargetOpContext[],
): boolean {
// Simple case: no member access, just a variable
if (postfixOps.length === 0) {
return this.signedVars.has(baseName);
}
// Member chain case: resolve through the chain
let currentType = this.varTypes.get(baseName);
Iif (!currentType) {
// Unknown base type - can't resolve, skip
return false;
}
// Walk through the postfix operations
for (const op of postfixOps) {
const memberIdent = op.IDENTIFIER();
if (memberIdent) {
// Member access: .fieldName
const fieldName = memberIdent.getText();
const fieldType = CodeGenState.getStructFieldType(
currentType,
fieldName,
);
Eif (!fieldType) {
// Unknown field - can't resolve, skip
return false;
}
currentType = fieldType;
} else E{
// Array subscript: [expr] - doesn't change the base type for primitives
// For arrays like u8[4], after [i] we still have u8
// Strip array dimensions if present
const bracketIndex = currentType.indexOf("[");
if (bracketIndex !== -1) {
currentType = currentType.substring(0, bracketIndex);
}
// Otherwise keep the type as-is (e.g., bit indexing on u8)
}
}
// Check if the final resolved type is signed
return TypeConstants.SIGNED_TYPES.includes(currentType);
}
/**
* Check if an additive expression contains a signed type operand
*/
private isSignedOperand(ctx: Parser.AdditiveExpressionContext): boolean {
// Walk down to unary expressions
const multExprs = ctx.multiplicativeExpression();
for (const multExpr of multExprs) {
const unaryExprs = multExpr.unaryExpression();
for (const unaryExpr of unaryExprs) {
if (this.isSignedUnaryExpression(unaryExpr)) {
return true;
}
}
}
return false;
}
/**
* Check if a unary expression is a signed type
*/
private isSignedUnaryExpression(ctx: Parser.UnaryExpressionContext): boolean {
// Check for MINUS prefix (negation) - indicates signed context
// Grammar: unaryExpression: MINUS unaryExpression | ...
if (ctx.MINUS()) {
const nestedUnary = ctx.unaryExpression();
Eif (nestedUnary) {
// If negating a literal, it's a negative number (signed)
const nestedPostfix = nestedUnary.postfixExpression();
Eif (nestedPostfix) {
const nestedPrimary = nestedPostfix.primaryExpression();
Eif (nestedPrimary?.literal()) {
return true;
}
}
// If negating a variable, check if it's signed
return this.isSignedUnaryExpression(nestedUnary);
}
return false;
}
const postfixExpr = ctx.postfixExpression();
Iif (!postfixExpr) return false;
const primaryExpr = postfixExpr.primaryExpression();
Iif (!primaryExpr) return false;
// Check for parenthesized expression
const parenExpr = primaryExpr.expression();
if (parenExpr) {
return this.isSignedExpression(parenExpr);
}
// Check for identifier that's a signed variable
const identifier = primaryExpr.IDENTIFIER();
if (identifier) {
return this.signedVars.has(identifier.getText());
}
// Positive integer literals are treated as unsigned
return false;
}
/**
* Check if a full expression contains signed operands
*/
private isSignedExpression(ctx: Parser.ExpressionContext): boolean {
const ternary = ctx.ternaryExpression();
Iif (!ternary) return false;
const additiveExprs = ExpressionUtils.collectAdditiveExpressions(ternary);
return additiveExprs.some((addExpr) => this.isSignedOperand(addExpr));
}
}
/**
* Analyzer that detects shift operations on signed integer types
*/
class SignedShiftAnalyzer {
private errors: ISignedShiftError[] = [];
/**
* Analyze the parse tree for signed shift operations
*/
public analyze(tree: Parser.ProgramContext): ISignedShiftError[] {
this.errors = [];
// First pass: collect signed variables and all variable types
const collector = new SignedVariableCollector();
ParseTreeWalker.DEFAULT.walk(collector, tree);
const signedVars = collector.getSignedVars();
const varTypes = collector.getVarTypes();
// Second pass: detect shift with signed operands
const listener = new SignedShiftListener(this, signedVars, varTypes);
ParseTreeWalker.DEFAULT.walk(listener, tree);
return this.errors;
}
/**
* Add a signed shift error
*/
public addError(line: number, column: number, operator: string): void {
this.errors.push({
code: "E0805",
line,
column,
message: `Shift operator '${operator}' not allowed on signed integer types`,
helpText:
"Shift operations on signed integers have undefined (<<) or implementation-defined (>>) behavior. Use unsigned types (u8, u16, u32, u64) for bit manipulation.",
});
}
/**
* Get all detected errors
*/
public getErrors(): ISignedShiftError[] {
return this.errors;
}
}
export default SignedShiftAnalyzer;
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