Skip to content

Limit unpack call in destructuring assignments to only required elements #1655

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
Perryvw merged 1 commit into from
Aug 23, 2025
Merged

Limit unpack call in destructuring assignments to only required elements #1655

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
29 changes: 29 additions & 0 deletions src/transformation/utils/lua-ast.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,35 @@ export function createUnpackCall(
return lua.setNodeFlags(lua.createCallExpression(unpack, [expression], tsOriginal), lua.NodeFlags.TableUnpackCall);
}

export function createBoundedUnpackCall(
context: TransformationContext,
expression: lua.Expression,
maxUnpackItem: number,
tsOriginal?: ts.Node
): lua.Expression {
if (context.luaTarget === LuaTarget.Universal) {
return transformLuaLibFunction(context, LuaLibFeature.Unpack, tsOriginal, expression);
}

// Lua 5.0 does not support this signature, so don't add the arguments there
const extraArgs =
context.luaTarget === LuaTarget.Lua50
? []
: [lua.createNumericLiteral(1), lua.createNumericLiteral(maxUnpackItem)];

const unpack =
context.luaTarget === LuaTarget.Lua50 ||
context.luaTarget === LuaTarget.Lua51 ||
context.luaTarget === LuaTarget.LuaJIT
? lua.createIdentifier("unpack")
: lua.createTableIndexExpression(lua.createIdentifier("table"), lua.createStringLiteral("unpack"));

return lua.setNodeFlags(
lua.createCallExpression(unpack, [expression, ...extraArgs], tsOriginal),
lua.NodeFlags.TableUnpackCall
);
}

export function isUnpackCall(node: lua.Node): boolean {
return lua.isCallExpression(node) && (node.flags & lua.NodeFlags.TableUnpackCall) !== 0;
}
Expand Down
4 changes: 2 additions & 2 deletions src/transformation/visitors/binary-expression/assignments.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ import * as lua from "../../../LuaAST";
import { TransformationContext } from "../../context";
import { validateAssignment } from "../../utils/assignment-validation";
import { createExportedIdentifier, getDependenciesOfSymbol, isSymbolExported } from "../../utils/export";
import { createUnpackCall, wrapInTable } from "../../utils/lua-ast";
import { createBoundedUnpackCall, wrapInTable } from "../../utils/lua-ast";
import { LuaLibFeature, transformLuaLibFunction } from "../../utils/lualib";
import { isArrayType, isDestructuringAssignment } from "../../utils/typescript";
import { isArrayLength, transformDestructuringAssignment } from "./destructuring-assignments";
Expand Down Expand Up @@ -252,7 +252,7 @@ export function transformAssignmentStatement(
} else {
right = context.transformExpression(expression.right);
if (!isMultiReturnCall(context, expression.right) && isArrayType(context, rightType)) {
right = createUnpackCall(context, right, expression.right);
right = createBoundedUnpackCall(context, right, expression.left.elements.length, expression.right);
}
}

Expand Down
7 changes: 4 additions & 3 deletions src/transformation/visitors/variable-declaration.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ import { FunctionVisitor, TransformationContext } from "../context";
import { validateAssignment } from "../utils/assignment-validation";
import { unsupportedVarDeclaration } from "../utils/diagnostics";
import { addExportToIdentifier } from "../utils/export";
import { createLocalOrExportedOrGlobalDeclaration, createUnpackCall, wrapInTable } from "../utils/lua-ast";
import { createBoundedUnpackCall, createLocalOrExportedOrGlobalDeclaration, wrapInTable } from "../utils/lua-ast";
import { LuaLibFeature, transformLuaLibFunction } from "../utils/lualib";
import { transformInPrecedingStatementScope } from "../utils/preceding-statements";
import { createCallableTable, isFunctionTypeWithProperties } from "./function";
Expand Down Expand Up @@ -209,10 +209,11 @@ export function transformBindingVariableDeclaration(
: lua.createNilLiteral();
statements.push(...createLocalOrExportedOrGlobalDeclaration(context, vars, values, initializer));
} else {
// local vars = this.transpileDestructingAssignmentValue(node.initializer);
const unpackedInitializer = createUnpackCall(
// use unpack(thing, 1, #bindingItems) to unpack
const unpackedInitializer = createBoundedUnpackCall(
context,
context.transformExpression(initializer),
bindingPattern.elements.length,
initializer
);
statements.push(
Expand Down
11 changes: 11 additions & 0 deletions test/unit/destructuring.spec.ts
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -195,6 +195,17 @@ describe("array destructuring optimization", () => {
.expectToMatchJsResult();
});

util.testEachVersion(
"array versions",
() =>
util.testFunction`
const array = [3, 5, 1];
const [a, b, c] = array;
return { a, b, c };
`,
util.expectEachVersionExceptJit(builder => builder.expectToMatchJsResult())
);

test("array literal", () => {
util.testFunction`
const [a, b, c] = [3, 5, 1];
Expand Down
Loading