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Fixit for missing @dynamicMemberLookup impl #83440

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Fixit for missing @dynamicMemberLookup impl #83440

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f6303a2
Add a fixit for missing @dynamicMemberLookup. Fix: #83344
doste Jul 26, 2025
ec1f8b6
Add NOTE 'add_subscript_method'
doste Jul 27, 2025
81d2dcc
Add a test for missing @dynamicMemberLookup
doste Jul 27, 2025
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3 changes: 3 additions & 0 deletions include/swift/AST/DiagnosticsSema.def
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Original file line number Diff line number Diff line change
Expand Up @@ -1727,6 +1727,9 @@ ERROR(invalid_dynamic_member_lookup_type,none,
"'@dynamicMemberLookup' requires %0 to have a "
"'subscript(dynamicMember:)' method that accepts either "
"'ExpressibleByStringLiteral' or a key path", (Type))
NOTE(add_subscript_method, none,
"add to %0 a 'subscript(dynamicMember:)' method that accepts "
"either 'ExpressibleByStringLiteral' or a key path", (Type))
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I don't think we need "add to <>" here because the note is attached to the declaration in question already.

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This could also be modeled similar to a "missing unwrap" diagnostic where there are two notes - one for ? and one for !, each with a dedicated fix-it.

NOTE(invalid_dynamic_member_subscript, none,
"add an explicit argument label to this subscript to satisfy "
"the '@dynamicMemberLookup' requirement", ())
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9 changes: 8 additions & 1 deletion lib/Sema/TypeCheckAttr.cpp
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Expand Up @@ -2106,6 +2106,7 @@ bool swift::isValidKeyPathDynamicMemberLookup(SubscriptDecl *decl,
return bool(getKeyPathTypeForDynamicMemberLookup(decl, ignoreLabel));
}


/// The @dynamicMemberLookup attribute is only allowed on types that have at
/// least one subscript member declared like this:
///
Expand Down Expand Up @@ -2161,8 +2162,14 @@ visitDynamicMemberLookupAttr(DynamicMemberLookupAttr *attr) {
return isValidDynamicMemberLookupSubscript(cand, /*ignoreLabel*/ true);
});

// If there were no potentially valid candidates, then throw an error.
// If there were no potentially valid candidates, then throw an error and emit a fix-it.
if (newCandidates.empty()) {

// Emit a fix-it to suggest the user to add a subscript method.
auto &d = ctx.Diags;
d.diagnose(decl->getLoc(), diag::add_subscript_method, type)
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Can call diagnostic directly on AttributeChecker here.

.fixItReplace(decl->getLoc(), "dynamicMember");
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I think this should suggest to add func subscript(dynamicMember member: <#Type#>) -> <#Result> {} stub.


emitInvalidTypeDiagnostic(attr->getLocation());
Comment on lines +2167 to 2173
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Notes are secondary diagnostics, i.e. they are always attached to a primary diagnostic such as a warning or error, so emission order is important — warning/error first, then its notes.

return;
}
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3 changes: 2 additions & 1 deletion test/attr/attr_dynamic_member_lookup.swift
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Expand Up @@ -191,7 +191,7 @@ func NotAllowedOnFunc() {}

// expected-error @+1 {{'@dynamicMemberLookup' requires 'InvalidBase' to have a 'subscript(dynamicMember:)' method that accepts either 'ExpressibleByStringLiteral' or a key path}}
@dynamicMemberLookup
class InvalidBase {}
class InvalidBase {} // expected-note {{add to 'InvalidBase' a 'subscript(dynamicMember:)' method that accepts either 'ExpressibleByStringLiteral' or a key path}}
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Please add a check to make sure that fix-it it positioned correctly, similar to https://github.com/swiftlang/swift/pull/83440/files#diff-146c63878b2e88e6d9540d0fbd3ba9c7987ca24f36fc6b22ca3de1aef17fe143R806


class InvalidDerived : InvalidBase { subscript(dynamicMember: String) -> Int { get {}} }

Expand Down Expand Up @@ -787,6 +787,7 @@ do {

// https://github.com/apple/swift/issues/52957


@dynamicMemberLookup
struct S1_52957 {
subscript(dynamicMember: String) -> String { // expected-error {{'@dynamicMemberLookup' requires 'S1_52957' to have a 'subscript(dynamicMember:)' method that accepts either 'ExpressibleByStringLiteral' or a key path}}
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