[Clang][AST] Let DeclPrinter print trailing requires expressions for template parameters

[zyn0217]

As discussed in #96084 (comment), it would be nice to present these trailing constraints on template parameters when printing CTAD decls through a DeclPrinter.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

Changes

As discussed in #96084 (comment), it would be nice to present these trailing constraints on template parameters when printing CTAD decls through a DeclPrinter.

---

Full diff: https://github.com/llvm/llvm-project/pull/96864.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+1)
• (modified) clang/lib/AST/DeclPrinter.cpp (+10)
• (modified) clang/test/PCH/cxx2a-requires-expr.cpp (+17)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 69aea6c21ad39..03b1daa6597cd 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -99,6 +99,7 @@ AST Dumping Potentially Breaking Changes
 ----------------------------------------
 
 - The text ast-dumper has improved printing of TemplateArguments.
+- The text decl-dumper prints template parameters' trailing requires expressions now.
 
 Clang Frontend Potentially Breaking Changes
 -------------------------------------------
diff --git a/clang/lib/AST/DeclPrinter.cpp b/clang/lib/AST/DeclPrinter.cpp
index 0cf4e64f83b8d..0a081e7e07ca8 100644
--- a/clang/lib/AST/DeclPrinter.cpp
+++ b/clang/lib/AST/DeclPrinter.cpp
@@ -1189,6 +1189,16 @@ void DeclPrinter::printTemplateParameters(const TemplateParameterList *Params,
   Out << '>';
   if (!OmitTemplateKW)
     Out << ' ';
+
+  if (const Expr *RequiresClause = Params->getRequiresClause()) {
+    if (OmitTemplateKW)
+      Out << ' ';
+    Out << "requires ";
+    RequiresClause->printPretty(Out, nullptr, Policy, Indentation, "\n",
+                                &Context);
+    if (!OmitTemplateKW)
+      Out << ' ';
+  }
 }
 
 void DeclPrinter::printTemplateArguments(ArrayRef<TemplateArgument> Args,
diff --git a/clang/test/PCH/cxx2a-requires-expr.cpp b/clang/test/PCH/cxx2a-requires-expr.cpp
index 7f8f258a0f8f3..936f601685463 100644
--- a/clang/test/PCH/cxx2a-requires-expr.cpp
+++ b/clang/test/PCH/cxx2a-requires-expr.cpp
@@ -22,3 +22,20 @@ bool f() {
     requires C<typename T::val> || (C<typename T::val> || C<T>);
   };
 }
+
+namespace trailing_requires_expression {
+
+template <typename T> requires C<T> && C2<T, T>
+// CHECK: template <typename T> requires C<T> && C2<T, T> void g();
+void g();
+
+template <typename T> requires C<T> || C2<T, T>
+// CHECK: template <typename T> requires C<T> || C2<T, T> constexpr int h = sizeof(T);
+constexpr int h = sizeof(T);
+
+template <typename T> requires C<T>
+// CHECK:      template <typename T> requires C<T> class i {
+// CHECK-NEXT: };
+class i {};
+
+}

[hokein]

thanks, looks good.