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[clang] Add frontend flag to enable support for broken external resugarers #102510

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[clang] Add frontend flag to enable support for broken external resugarers #102510

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1 change: 1 addition & 0 deletions clang/include/clang/Basic/LangOptions.def
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Original file line number Diff line number Diff line change
Expand Up @@ -162,6 +162,7 @@ LANGOPT(CoroAlignedAllocation, 1, 0, "prefer Aligned Allocation according to P20
LANGOPT(DllExportInlines , 1, 1, "dllexported classes dllexport inline methods")
LANGOPT(RelaxedTemplateTemplateArgs, 1, 1, "C++17 relaxed matching of template template arguments")
LANGOPT(ExperimentalLibrary, 1, 0, "enable unstable and experimental library features")
LANGOPT(SupportBrokenExternalResugarers, 1, 0, "Suppress transforms which would impede broken external resugarers")

LANGOPT(PointerAuthIntrinsics, 1, 0, "pointer authentication intrinsics")
LANGOPT(PointerAuthCalls , 1, 0, "function pointer authentication")
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5 changes: 5 additions & 0 deletions clang/include/clang/Driver/Options.td
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Expand Up @@ -3449,6 +3449,11 @@ defm relaxed_template_template_args : BoolFOption<"relaxed-template-template-arg
PosFlag<SetTrue, [], [], "Enable">,
NegFlag<SetFalse, [], [CC1Option], "Disable">,
BothFlags<[], [ClangOption], " C++17 relaxed template template argument matching">>;
defm support_broken_external_resugarers : BoolFOption<"support-broken-external-resugarers",
LangOpts<"SupportBrokenExternalResugarers">, DefaultFalse,
PosFlag<SetTrue, [], [CC1Option], "Enable">,
NegFlag<SetFalse, [], [], "Disable">,
BothFlags<[], [], " support for broken external resugarers">>;
defm sized_deallocation : BoolFOption<"sized-deallocation",
LangOpts<"SizedDeallocation">, Default<cpp14.KeyPath>,
PosFlag<SetTrue, [], [], "Enable C++14 sized global deallocation functions">,
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11 changes: 9 additions & 2 deletions clang/lib/Sema/SemaTemplate.cpp
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Expand Up @@ -3333,9 +3333,16 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
return QualType();

// Only substitute for the innermost template argument list.
// NOTE: Some external resugarers rely on leaving a Subst* node here.
// Make the substituion non-final in that case.
// Note that these external resugarers are essentially broken
// for depending on this, because we don't provide
// enough context in the Subst* nodes in order
// to tell different template type alias specializations apart.
MultiLevelTemplateArgumentList TemplateArgLists;
TemplateArgLists.addOuterTemplateArguments(Template, SugaredConverted,
/*Final=*/true);
TemplateArgLists.addOuterTemplateArguments(
Template, SugaredConverted,
/*Final=*/!getLangOpts().SupportBrokenExternalResugarers);
TemplateArgLists.addOuterRetainedLevels(
AliasTemplate->getTemplateParameters()->getDepth());

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18 changes: 18 additions & 0 deletions clang/test/AST/ast-dump-support-broken-external-resugarers.cpp
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@@ -0,0 +1,18 @@
// RUN: %clang_cc1 -fsyntax-only -fsupport-broken-external-resugarers -ast-dump -ast-dump-filter=dump %s | FileCheck -strict-whitespace %s

namespace t1 {
template<class T> using X = T;
using dump = X<int>;

// CHECK-LABEL: Dumping t1::dump:
// CHECK-NEXT: TypeAliasDecl
// CHECK-NEXT: `-ElaboratedType
// CHECK-NEXT: `-TemplateSpecializationType
// CHECK-NEXT: |-name: 'X':'t1::X' qualified
// CHECK-NEXT: | `-TypeAliasTemplateDecl
// CHECK-NEXT: |-TemplateArgument
// CHECK-NEXT: | `-BuiltinType {{.+}} 'int'
// CHECK-NEXT: `-SubstTemplateTypeParmType 0x{{[0-9]+}} 'int' sugar class depth 0 index 0 T
// CHECK-NEXT: |-TypeAliasTemplate {{.+}} 'X'
// CHECK-NEXT: `-BuiltinType {{.+}} 'int'
} // namespace t1
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