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Fix try/catch/finally flow #1729

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Merged
Perryvw merged 3 commits into from
Jun 30, 2026
Merged

Fix try/catch/finally flow #1729

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5238499
Fix try/catch/finally flow
SuperPaintman Jun 28, 2026
5f25852
Fix comment
SuperPaintman Jun 28, 2026
c8d8148
Run prettier
SuperPaintman Jun 29, 2026
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50 changes: 40 additions & 10 deletions src/transformation/visitors/errors.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -165,6 +165,7 @@ export const transformTryStatement: FunctionVisitor<ts.TryStatement> = (statemen

const tryResultIdentifier = lua.createIdentifier("____try");
const returnValueIdentifier = lua.createIdentifier("____returnValue");
const rethrowIdentifier = lua.createIdentifier("____rethrow");

const result: lua.Statement[] = [];

Expand All @@ -191,6 +192,9 @@ export const transformTryStatement: FunctionVisitor<ts.TryStatement> = (statemen
}
}
result.push(lua.createVariableDeclarationStatement(tryReturnIdentifiers, tryCall));
if (statement.finallyBlock) {
result.push(lua.createVariableDeclarationStatement(rethrowIdentifier));
}

const catchCall = lua.createCallExpression(
catchIdentifier,
Expand All @@ -203,8 +207,22 @@ export const transformTryStatement: FunctionVisitor<ts.TryStatement> = (statemen
)
: lua.createExpressionStatement(catchCall);

const catchCallFunction = lua.createFunctionExpression(lua.createBlock([catchCallStatement]));

const tryCatchCall = lua.createCallExpression(pCall, [catchCallFunction]);

const tryCatchCallStatement = lua.createAssignmentStatement(
[lua.cloneIdentifier(tryResultIdentifier), lua.cloneIdentifier(rethrowIdentifier)],
tryCatchCall
);

const notTryCondition = lua.createUnaryExpression(tryResultIdentifier, lua.SyntaxKind.NotOperator);
result.push(lua.createIfStatement(notTryCondition, lua.createBlock([catchCallStatement])));
result.push(
lua.createIfStatement(
notTryCondition,
lua.createBlock(statement.finallyBlock ? [tryCatchCallStatement] : [catchCallStatement])
)
);
} else if (tryScope.functionReturned) {
// try with return, but no catch
// returnedIdentifier = lua.createIdentifier("____returned");
Expand All @@ -230,21 +248,33 @@ 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 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) {
if (statement.finallyBlock) {
const notTryCondition = lua.createUnaryExpression(
lua.cloneIdentifier(tryResultIdentifier),
lua.SyntaxKind.NotOperator
);
const errorIdentifier = tryScope.functionReturned
? lua.cloneIdentifier(returnedIdentifier)
: lua.createIdentifier("____error");
const rethrow = lua.createExpressionStatement(
lua.createCallExpression(lua.createIdentifier("error"), [errorIdentifier, lua.createNumericLiteral(0)])
);
result.push(lua.createIfStatement(notTryCondition, lua.createBlock([rethrow])));

if (!statement.catchClause) {
const errorIdentifier = tryScope.functionReturned
? lua.cloneIdentifier(returnedIdentifier)
: lua.createIdentifier("____error");
const rethrow = lua.createExpressionStatement(
lua.createCallExpression(lua.createIdentifier("error"), [errorIdentifier, lua.createNumericLiteral(0)])
);
result.push(lua.createIfStatement(notTryCondition, lua.createBlock([rethrow])));
} else if (statement.catchClause.block.statements.length > 0) {
// Re-throw is possible only from non-empty blocks.
const rethrow = lua.createExpressionStatement(
lua.createCallExpression(lua.createIdentifier("error"), [
rethrowIdentifier,
lua.createNumericLiteral(0),
])
);
result.push(lua.createIfStatement(notTryCondition, lua.createBlock([rethrow])));
}
}

if (returnCondition && returnedIdentifier) {
Expand Down
29 changes: 19 additions & 10 deletions test/unit/error.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -7,31 +7,40 @@ test("throwString", () => {
`.expectToEqual(new util.ExecutionError("Some Error"));
});

// TODO: Finally does not behave like it should, see #1137
// eslint-disable-next-line jest/no-disabled-tests
test.skip.each([0, 1, 2])("re-throw (%p)", i => {
test.each([
{ innerTry: false, innerFinally: false, outerFinally: false },
{ innerTry: false, innerFinally: false, outerFinally: true },
{ innerTry: false, innerFinally: true, outerFinally: false },
{ innerTry: false, innerFinally: true, outerFinally: true },
{ innerTry: true, innerFinally: false, outerFinally: false },
{ innerTry: true, innerFinally: false, outerFinally: true },
{ innerTry: true, innerFinally: true, outerFinally: false },
{ innerTry: true, innerFinally: true, outerFinally: true },
])("re-throw (%j)", o => {
util.testFunction`
const i: number = ${i};
const innerTry: boolean = ${o.innerTry};
const innerFinally: boolean = ${o.innerFinally};
const outerFinally: boolean = ${o.outerFinally};
function foo() {
try {
try {
if (i === 0) { throw "z"; }
if (innerTry) { throw "inner.try"; }
} catch (e) {
throw "a";
throw (e as string) + "->" + "inner.catch";
} finally {
if (i === 1) { throw "b"; }
if (innerFinally) { throw "inner.finally"; }
}
} catch (e) {
throw (e as string).toUpperCase();
throw (e as string) + "->" + "outer.catch";
} finally {
throw "C";
if (outerFinally) { throw "outer.finally"; }
}
}
let result: string = "x";
try {
foo();
} catch (e) {
result = (e as string)[(e as string).length - 1];
result = e as string;
}
return result;
`.expectToMatchJsResult();
Expand Down
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