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* Return-Value Use Analyzer (ADR-070, E0708)
*
* Rejects a non-void function call used as a bare expression statement, unless
* the author explicitly discarded it with a cast to void:
*
* next(); // E0708 -- return value discarded
* (void) next(); // OK -- explicitly discarded
* u32 v <- next(); // OK -- used
*
* ADR-070 splits discarded returns into two cases. This analyzer owns **Case 2**
* (the author wrote the call). Case 1 -- calls the transpiler itself emits while
* lowering string operations -- is codegen, and is cast to void at the single
* emit site in StringUtils. The two never disagree because neither re-derives
* the other's decision: an author-written call reaches this analyzer, a
* transpiler-emitted one never exists at the C-Next source level at all.
*
* Domain boundary: a callee whose return type C-Next cannot resolve is outside
* the rule, not an exception to it -- you cannot check a return type you cannot
* see. This is ADR-070's "enforce where resolvable" boundary.
*
* `safe_div`/`safe_mod` (ADR-051) are deliberately NOT exempt. An earlier draft
* of ADR-070 carved them out on the premise that they have "no bound return" at
* the C-Next level; authors bind it constantly (`err <- safe_div(...)`), and the
* same ADR names "a discarded `safe_div` outcome" as a motivating example of the
* bug this rule prevents. They are ordinary non-void functions here.
*/
import { ParseTreeWalker } from "antlr4ng";
import { CNextListener } from "../../PARSE/2-Parse/grammar/CNextListener";
import * as Parser from "../../PARSE/2-Parse/grammar/CNextParser";
import StdlibFunctions from "./StdlibFunctions";
import CalleeNameResolver from "./helpers/CalleeNameResolver";
import EnclosingScope from "./helpers/EnclosingScope";
import IReturnValueUseError from "./types/IReturnValueUseError";
import type SymbolTable from "../../PARSE/3-Declare/SymbolTable";
import DeclaredTypeFacts from "../../utils/DeclaredTypeFacts";
import type IAnalysisContext from "./types/IAnalysisContext";
class ReturnValueUseListener extends CNextListener {
public readonly errors: IReturnValueUseError[] = [];
/** Enclosing `scope`, so `this.member()` resolves to Scope__member (#1357). */
private readonly enclosing = new EnclosingScope();
/** Scope names in this file, for resolving `global.Scope.member()`. */
private readonly knownScopes: ReadonlySet<string>;
constructor(
knownScopes: ReadonlySet<string>,
private readonly symbolTable: SymbolTable,
private readonly context: IAnalysisContext,
) {
super();
this.knownScopes = knownScopes;
}
override enterScopeDeclaration = (
ctx: Parser.ScopeDeclarationContext,
): void => {
this.enclosing.enter(ctx.IDENTIFIER()?.getText() ?? "");
};
override exitScopeDeclaration = (): void => {
this.enclosing.exit();
};
override enterExpressionStatement = (
ctx: Parser.ExpressionStatementContext,
): void => {
const expr = ctx.expression();
Iif (!expr) return;
// An explicit `(void)` discard satisfies the rule outright.
if (ReturnValueUseAnalyzer.isVoidCast(expr)) return;
const postfix = ReturnValueUseAnalyzer.asBareCall(expr);
if (!postfix) return;
const resolved = CalleeNameResolver.resolveDetailed(
postfix,
this.enclosing.current(),
// Scopes reached through an included .cnx are not in this file's
// declarations; CodeGenState.knownScopes is merged across includes.
(name) =>
this.knownScopes.has(name) ||
DeclaredTypeFacts.isScope(this.context.symbols, name),
);
Iif (!resolved) return;
const funcName = ReturnValueUseAnalyzer.nonVoidCallee(
resolved,
this.enclosing.current(),
this.symbolTable,
this.context,
);
if (!funcName) return;
this.errors.push({
line: ctx.start?.line ?? 0,
column: ctx.start?.column ?? 0,
code: "E0708",
message: `Return value of non-void function '${funcName}' is discarded`,
helpText: `Use the value, or discard it explicitly: (void) ${funcName}(...);`,
});
};
}
class ReturnValueUseAnalyzer {
/**
* True when the statement's expression is a cast to void wrapping anything.
* Uses the existing ADR-017 cast expression -- no new syntax (ADR-070).
*/
static isVoidCast(expr: Parser.ExpressionContext): boolean {
const cast = ReturnValueUseAnalyzer.findCast(expr);
return cast?.type()?.getText() === "void";
}
/** Descend single-child wrappers looking for a castExpression. */
private static findCast(
node: Parser.ExpressionContext | null,
): Parser.CastExpressionContext | null {
let current: unknown = node;
while (current && typeof current === "object") {
if (current instanceof Parser.CastExpressionContext) return current;
const ctx = current as {
getChildCount?: () => number;
getChild?: (i: number) => unknown;
};
if (
typeof ctx.getChildCount !== "function" ||
ctx.getChildCount() !== 1
) {
return null;
}
current = ctx.getChild!(0);
}
return null;
}
/**
* Return the postfix expression when the whole statement is exactly one call.
* `foo().field;` is deliberately not a bare call -- ADR-070 puts that form
* out of scope.
*/
static asBareCall(
expr: Parser.ExpressionContext,
): Parser.PostfixExpressionContext | null {
let current: unknown = expr;
while (current && typeof current === "object") {
if (current instanceof Parser.PostfixExpressionContext) {
const ops = current.postfixOp();
// A cast wraps the call one level deeper: `(void) f()` and `(u32) f()`
// both parse as a postfix whose primary IS the cast. Descend rather
// than stop -- stopping here would accept every cast-shaped discard
// without ever consulting the cast's type, which is what makes the
// `(void)` form special.
const cast = current.primaryExpression().castExpression();
if (ops.length === 0 && cast) {
current = cast.unaryExpression();
continue;
}
const last = ops.at(-1);
// The final op must be the call itself, or the statement's value is a
// member/subscript of a call result rather than the call.
if (!last || !ReturnValueUseAnalyzer.isCallOp(last)) return null;
return current;
}
const ctx = current as {
getChildCount?: () => number;
getChild?: (i: number) => unknown;
};
Iif (
typeof ctx.getChildCount !== "function" ||
ctx.getChildCount() !== 1
) {
return null;
}
current = ctx.getChild!(0);
}
return null;
}
private static isCallOp(op: Parser.PostfixOpContext): boolean {
return op.argumentList() !== null || op.getText().startsWith("(");
}
/**
* The name to report, or null when this call has no value to discard.
*
* ADR-057: a bare `read()` inside a scope means `this.read()`, but return
* types are keyed by transpiled C name -- so the bare spelling misses the
* lookup the qualified one hits, and the discard would be accepted on the
* form CLAUDE.md makes house style. Retry against the scope-qualified
* candidate before concluding there is nothing to check.
*/
static nonVoidCallee(
resolved: { name: string; isGlobalCall: boolean },
currentScopePath: string,
symbolTable: SymbolTable,
context: IAnalysisContext,
): string | null {
if (
ReturnValueUseAnalyzer.returnsAValue(resolved.name, symbolTable, context)
) {
return resolved.name;
}
const fallback = CalleeNameResolver.scopeQualifiedCandidate(
resolved.name,
currentScopePath,
resolved.isGlobalCall,
);
Iif (
fallback &&
ReturnValueUseAnalyzer.returnsAValue(fallback, symbolTable, context)
) {
return fallback;
}
return null;
}
/**
* True only when C-Next can see a non-void return type for `name`.
* Unresolvable names answer false: outside the rule's domain, not exempt.
*/
static returnsAValue(
name: string,
symbolTable: SymbolTable,
context: IAnalysisContext,
): boolean {
const builtin = StdlibFunctions.builtinReturnType(name);
if (builtin !== null) {
return builtin !== "void";
}
const declared = context.symbols.functionReturnTypes.get(name);
if (declared !== undefined) {
return declared !== "void";
}
// Functions declared in included C/C++ headers reach the analyzer through
// the symbol table rather than through CodeGenState.symbols, which only
// merges .cnx includes. ADR-070 rejects blanket-exempting external C
// precisely because these returns ARE visible -- just by a different route.
const external = ReturnValueUseAnalyzer.externalReturnType(
name,
symbolTable,
);
if (external !== null) {
return external !== "void";
}
if (StdlibFunctions.isKnown(name)) {
return !StdlibFunctions.returnsVoid(name);
}
return false;
}
/**
* Return type of a function declared in an included C/C++ header.
*
* C symbols carry their types as plain strings and live in a different part
* of the symbol table from C-Next symbols (`getCSymbol`, not the TSymbol
* index), so they need their own lookup. ADR-070 rejects blanket-exempting
* external C precisely because these returns are visible -- they just arrive
* by a different route than CodeGenState.symbols, which merges only .cnx
* includes.
*/
static externalReturnType(
name: string,
symbolTable: SymbolTable,
): string | null {
// .hpp symbols land in a separate index from .h ones; ICppFunctionSymbol
// is structurally identical, so one lookup covers both.
//
// #1456: the `?.` on the table AND on both methods is gone. Neither can be
// absent -- `SymbolTable` declares both -- so the optional call was a guard
// that could not fire, and it would have turned a genuinely missing method
// into `null`, which reads here as "this function returns nothing" rather
// than as an error.
const sym = symbolTable.getCSymbol(name) ?? symbolTable.getCppSymbol(name);
if (sym?.kind !== "function") return null;
return sym.type ?? null;
}
/** Scope names declared in this file. */
private static collectScopes(
tree: Parser.ProgramContext,
): ReadonlySet<string> {
const scopes = new Set<string>();
for (const decl of tree.declaration()) {
const scopeDecl = decl.scopeDeclaration();
if (scopeDecl) {
scopes.add(scopeDecl.IDENTIFIER().getText());
}
}
return scopes;
}
/** Run the analysis over a parsed program. */
static analyze(
tree: Parser.ProgramContext,
symbolTable: SymbolTable,
context: IAnalysisContext,
): IReturnValueUseError[] {
const listener = new ReturnValueUseListener(
ReturnValueUseAnalyzer.collectScopes(tree),
symbolTable,
context,
);
ParseTreeWalker.DEFAULT.walk(listener, tree);
return listener.errors;
}
}
export default ReturnValueUseAnalyzer;
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