Rework ForEachStmt Desugaring #86010
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elsakeirouz
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elsakeirouz
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Dec 13, 2025
elsakeirouz
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elsakeirouz
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| return ctx.getAsyncIteratorNext(); | ||
| } | ||
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| static BraceStmt *desugarForEachStmt(ForEachStmt* stmt){ |
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Potentially refactor this function to make it more readable.
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I have not yet tested any behavior of generated SIL code but it seems reasonable in comparison. I was able to compile the standard library. Here: * include/swift/AST/ASTBridging.h, * include/swift/AST/Expr.h, * include/swift/AST/ExprNodes.def, * include/swift/AST/Stmt.h, * include/swift/AST/StmtNodes.def, * include/swift/AST/TypeCheckRequests.h, * include/swift/AST/TypeCheckerTypeIDZone.def, * include/swift/Sema/ConstraintLocator.h, * include/swift/Sema/SyntacticElementTarget.h, * lib/AST/ASTDumper.cpp, * lib/AST/ASTPrinter.cpp, * lib/AST/ASTScopeCreation.cpp, * lib/AST/ASTVerifier.cpp, * lib/AST/ASTWalker.cpp, * lib/AST/Bridging/StmtBridging.cpp, * lib/AST/Expr.cpp, * lib/AST/Stmt.cpp, * lib/AST/TypeCheckRequests.cpp, * lib/ASTGen/Sources/ASTGen/Stmts.swift, * lib/Parse/ParseStmt.cpp, * lib/SILGen/ASTVisitor.h, * lib/SILGen/SILGenExpr.cpp, * lib/SILGen/SILGenStmt.cpp, * lib/SILOptimizer/Mandatory/MoveOnlyDiagnostics.cpp, * lib/Sema/BuilderTransform.cpp, * lib/Sema/CSApply.cpp, * lib/Sema/CSDiagnostics.cpp, * lib/Sema/CSGen.cpp, * lib/Sema/CSSimplify.cpp, * lib/Sema/CSSyntacticElement.cpp, * lib/Sema/SyntacticElementTarget.cpp, * lib/Sema/TypeCheckEffects.cpp, * lib/Sema/TypeCheckStmt.cpp.
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This PR aims to lift the desugaring of ForEachStmt (when dealing with Sequences) from SILGen to the AST, and simultaneously delaying the synthesis of makeIterator and next calls until after typechecking.
The motivation for this is support for non-Copyable & non-Escapable sequences with non-Copyable elements in ForEachStmt. In order to know which variant of makeIterator and next calls we need, we must determine whether a Sequence is copyable, asynchronous, or neither. The compiler currently relies on the function choice to infer the type of the elements. However, to determine whether a Sequence is copyable, it must be typed.
For that reason, instead of matching the pattern type with the unwrapped result type of next(), we're now matching it with Sequence. This allows us to delay the decision and synthesis of those function calls until later.
Additionally, in order to avoid having to translate the rest of the complex desugar logic for the borrowing ForEachStmt in SILGen, we chose to represent it directly at the AST level, which SILGen will then use to emit the corresponding SIL code.
To make things simpler all around, we chose to start by reworking this pass for the regular/async ForEachStmts before handling borrowing statements.
We expect to be able to remove ConstraintKind::ValueWitness with this work.