swiftlang/swift

Missing fixits for missing @dynamicMemberLookup impl

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#83,344 opened on Jul 25, 2025

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@dynamicMemberLookupattributesbugcompilerdiagnostics qualityfix-itsgood first issueswift 6.2type checker

Description

Description

if you haven't implemented the dynamic member lookup requirements the compiler emits an error without fixits:

test.swift:1:1: error: '@dynamicMemberLookup' requires 'Test' to have a 'subscript(dynamicMember:)' method that accepts either 'ExpressibleByStringLiteral' or a key path
1 | @dynamicMemberLookup
  | `- error: '@dynamicMemberLookup' requires 'Test' to have a 'subscript(dynamicMember:)' method that accepts either 'ExpressibleByStringLiteral' or a key path
2 | struct Test {}
3 |

Reproduction

@dynamicMemberLookup
struct Test {}

Expected behavior

fixits with error message

Environment

Apple Swift version 6.2 (swiftlang-6.2.0.13.10 clang-1700.3.13.4) Target: arm64-apple-macosx26.0

Additional information

No response

Contributor guide

Tech stack
swiftcpp
Domain
toolingdeveloper experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Swift languageCompiler diagnosticsC++
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
The error is emitted during semantic analysis in the Swift compiler. Look for the diagnostic in 'lib/Sema/TypeCheckDecl.cpp' where '@dynamicMemberLookup' requirements are checked. Add a fix it suggestion to insert the missing subscript method. Study existing fixit implementations in the same file for patterns.
Missing fixits for missing @dynamicMemberLookup impl · swiftlang/swift#83344 | Good First Issue