From f8e4eca237eb0dac715c6b9601e1f5289227c65b Mon Sep 17 00:00:00 2001 From: Perryvw Date: Fri, 22 Aug 2025 22:35:31 +0200 Subject: [PATCH] Limit unpack call in destructuring assignments to only required elements --- src/transformation/utils/lua-ast.ts | 29 +++++++++++++++++++ .../visitors/binary-expression/assignments.ts | 4 +-- .../visitors/variable-declaration.ts | 7 +++-- test/unit/destructuring.spec.ts | 11 +++++++ 4 files changed, 46 insertions(+), 5 deletions(-) diff --git a/src/transformation/utils/lua-ast.ts b/src/transformation/utils/lua-ast.ts index b947e0bf6..59f6cffd7 100644 --- a/src/transformation/utils/lua-ast.ts +++ b/src/transformation/utils/lua-ast.ts @@ -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; } diff --git a/src/transformation/visitors/binary-expression/assignments.ts b/src/transformation/visitors/binary-expression/assignments.ts index 3e246c3f8..73e6d9dd1 100644 --- a/src/transformation/visitors/binary-expression/assignments.ts +++ b/src/transformation/visitors/binary-expression/assignments.ts @@ -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"; @@ -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); } } diff --git a/src/transformation/visitors/variable-declaration.ts b/src/transformation/visitors/variable-declaration.ts index 082ef9a6b..f15ed0115 100644 --- a/src/transformation/visitors/variable-declaration.ts +++ b/src/transformation/visitors/variable-declaration.ts @@ -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"; @@ -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( diff --git a/test/unit/destructuring.spec.ts b/test/unit/destructuring.spec.ts index 80d3d482c..65ecf95a3 100644 --- a/test/unit/destructuring.spec.ts +++ b/test/unit/destructuring.spec.ts @@ -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];