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fix try/finally rethrow when try block has return paths #1699

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fix try/finally rethrow when try block has return paths #1699

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13 changes: 7 additions & 6 deletions src/transformation/visitors/errors.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -159,18 +159,19 @@ export const transformTryStatement: FunctionVisitor<ts.TryStatement> = (statemen
result.push(...context.transformStatements(statement.finallyBlock));
}

// Re-throw error if try had no catch but had a finally
// Re-throw error if try had no catch but had a finally.
// On pcall failure the error is the second return value, which lands in
// ____hasReturned (when functionReturned) or ____error (otherwise).
if (!statement.catchClause && statement.finallyBlock) {
const notTryCondition = lua.createUnaryExpression(
lua.cloneIdentifier(tryResultIdentifier),
lua.SyntaxKind.NotOperator
);
const errorIdentifier = lua.createIdentifier("____error");
const errorIdentifier = tryScope.functionReturned
? lua.cloneIdentifier(returnedIdentifier)
: lua.createIdentifier("____error");
const rethrow = lua.createExpressionStatement(
lua.createCallExpression(lua.createIdentifier("error"), [
lua.cloneIdentifier(errorIdentifier),
lua.createNumericLiteral(0),
])
lua.createCallExpression(lua.createIdentifier("error"), [errorIdentifier, lua.createNumericLiteral(0)])
);
result.push(lua.createIfStatement(notTryCondition, lua.createBlock([rethrow])));
}
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55 changes: 55 additions & 0 deletions test/unit/error.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -417,6 +417,61 @@ test("sourceMapTraceback maps anonymous function locations in .lua files (#1665)
expect(result).toContain("<main.ts:2>");
});

test("try/finally rethrow preserves error value", () => {
util.testFunction`
function foo() {
try {
throw "oops";
} finally {
}
}
try { foo(); return "no error"; } catch(e) { return e; }
`.expectToMatchJsResult();
});

test("try/finally with return and throw paths", () => {
util.testFunction`
function foo(shouldReturn: boolean) {
try {
if (shouldReturn) return "returned";
throw "thrown";
} finally {
}
}
const results: any[] = [];
results.push(foo(true));
try { foo(false); } catch(e) { results.push(e); }
return results;
`.expectToMatchJsResult();
});

test("try/finally runs finally side effect before rethrow", () => {
util.testFunction`
let sideEffect = false;
function foo() {
try {
throw "err";
} finally {
sideEffect = true;
}
}
try { foo(); } catch(e) {}
return sideEffect;
`.expectToMatchJsResult();
});

test("try/finally rethrow with non-string error", () => {
util.testFunction`
function foo() {
try {
throw 42;
} finally {
}
}
try { foo(); return "no error"; } catch(e) { return e; }
`.expectToMatchJsResult();
});

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@lolleko lolleko Mar 28, 2026

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Can we have one more test for return + throw + non-empty finally body

function foo(shouldReturn: boolean) {
    try {
        if (shouldReturn) return "ok";
        throw "err";
    } finally {
        sideEffect = true; // must still run on both paths
    }
}

util.testEachVersion(
"error stacktrace omits constructor and __TS_New",
() => util.testFunction`
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