https://github.com/ymand updated 
https://github.com/llvm/llvm-project/pull/103219

>From cde9e0eb8090a95df22bc83527a68d385fa847a9 Mon Sep 17 00:00:00 2001
From: Matheus Izvekov <mizve...@gmail.com>
Date: Thu, 8 Aug 2024 14:22:03 -0300
Subject: [PATCH 1/2] [clang] Add frontend flag to enable support for broken
 external resugarers

There are some external projects that can't rely on our own sugar
propagation for templated entities, because they need to resugar types
which only exist within their framework, and so are entirely invisible
to our internal tooling.

This new flag is meant to prevent our transforms from removing any Subst*
nodes.

For this, this is wired only to template type alias subsititutions.

Note that our AST does represent enough information to correctly
resugar template type alias, so any users of this are either defective
or working under extremely limited scenarios.
---
 clang/include/clang/Basic/LangOptions.def      |  1 +
 clang/include/clang/Driver/Options.td          |  5 +++++
 clang/lib/Sema/SemaTemplate.cpp                | 11 +++++++++--
 ...dump-support-broken-external-resugarers.cpp | 18 ++++++++++++++++++
 4 files changed, 33 insertions(+), 2 deletions(-)
 create mode 100644 
clang/test/AST/ast-dump-support-broken-external-resugarers.cpp

diff --git a/clang/include/clang/Basic/LangOptions.def 
b/clang/include/clang/Basic/LangOptions.def
index ca9c00a1473bbd..de1f441124b2ec 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -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")
diff --git a/clang/include/clang/Driver/Options.td 
b/clang/include/clang/Driver/Options.td
index 75320cafaefa5f..4c1b9d2b059add 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3455,6 +3455,11 @@ 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">,
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 29e7978ba5b1f8..1a1b39519ac7c7 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -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());
 
diff --git a/clang/test/AST/ast-dump-support-broken-external-resugarers.cpp 
b/clang/test/AST/ast-dump-support-broken-external-resugarers.cpp
new file mode 100644
index 00000000000000..2f2e4ce16bcdd1
--- /dev/null
+++ b/clang/test/AST/ast-dump-support-broken-external-resugarers.cpp
@@ -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

>From f1f72b0f164ce649c1c3a20176160d579fa8da6a Mon Sep 17 00:00:00 2001
From: Yitzhak Mandelbaum <yitzh...@google.com>
Date: Tue, 13 Aug 2024 14:47:02 +0000
Subject: [PATCH 2/2] fixup! [clang] Add frontend flag to enable support for
 broken external resugarers

rename flag and adjust the comments
---
 clang/include/clang/Basic/LangOptions.def         |  2 +-
 clang/include/clang/Driver/Options.td             |  7 ++++---
 clang/lib/Sema/SemaTemplate.cpp                   | 15 +++++++--------
 ...st-dump-support-broken-external-resugarers.cpp |  2 +-
 4 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/clang/include/clang/Basic/LangOptions.def 
b/clang/include/clang/Basic/LangOptions.def
index de1f441124b2ec..6086f0ee73d27c 100644
--- a/clang/include/clang/Basic/LangOptions.def
+++ b/clang/include/clang/Basic/LangOptions.def
@@ -162,7 +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(RetainSubstTemplateTypeParmTypeAstNodes, 1, 0, "retain 
SubstTemplateTypeParmType nodes in the AST's representationof alias template 
specializations")
 
 LANGOPT(PointerAuthIntrinsics, 1, 0, "pointer authentication intrinsics")
 LANGOPT(PointerAuthCalls  , 1, 0, "function pointer authentication")
diff --git a/clang/include/clang/Driver/Options.td 
b/clang/include/clang/Driver/Options.td
index 4c1b9d2b059add..6df3a6a5943a97 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3455,11 +3455,12 @@ 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,
+defm retain_subst_template_type_parm_type_ast_nodes : 
BoolFOption<"retain-subst-template-type-parm-type-ast-nodes",
+  LangOpts<"RetainSubstTemplateTypeParmTypeAstNodes">, DefaultFalse,
   PosFlag<SetTrue, [], [CC1Option], "Enable">,
   NegFlag<SetFalse, [], [], "Disable">,
-  BothFlags<[], [], " support for broken external resugarers">>;
+  BothFlags<[], [], " retain SubstTemplateTypeParmType nodes in the AST's 
representation"
+  " of alias template specializations">>;
 defm sized_deallocation : BoolFOption<"sized-deallocation",
   LangOpts<"SizedDeallocation">, Default<cpp14.KeyPath>,
   PosFlag<SetTrue, [], [], "Enable C++14 sized global deallocation functions">,
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 1a1b39519ac7c7..876921a6b311d4 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -3332,17 +3332,16 @@ QualType Sema::CheckTemplateIdType(TemplateName Name,
     if (Pattern->isInvalidDecl())
       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.
+    // Only substitute for the innermost template argument list.  NOTE: Some
+    // external resugarers rely on leaving a Subst* node here.  Make the
+    // substitution non-final in that case.  Note that these external 
resugarers
+    // will still miss some information in this representation, 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=*/!getLangOpts().SupportBrokenExternalResugarers);
+        /*Final=*/!getLangOpts().RetainSubstTemplateTypeParmTypeAstNodes);
     TemplateArgLists.addOuterRetainedLevels(
         AliasTemplate->getTemplateParameters()->getDepth());
 
diff --git a/clang/test/AST/ast-dump-support-broken-external-resugarers.cpp 
b/clang/test/AST/ast-dump-support-broken-external-resugarers.cpp
index 2f2e4ce16bcdd1..de1a1051a09933 100644
--- a/clang/test/AST/ast-dump-support-broken-external-resugarers.cpp
+++ b/clang/test/AST/ast-dump-support-broken-external-resugarers.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -fsyntax-only -fsupport-broken-external-resugarers 
-ast-dump -ast-dump-filter=dump %s | FileCheck -strict-whitespace %s
+// RUN: %clang_cc1 -fsyntax-only 
-fretain-subst-template-type-parm-type-ast-nodes -ast-dump 
-ast-dump-filter=dump %s | FileCheck -strict-whitespace %s
 
 namespace t1 {
 template<class T> using X = T;

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