[clang] Fix ConceptSpecializationExpr::getEndLoc()

[nridge]

Summary

It returned an invalid location in case of a constrained-parameter
with no explicit arguments.

[nridge]

Spun off from D84136. Depends on D84461.

[hokein]

clang/test/AST/ast-dump-concepts.cpp

19–20

could you also verify what's the end loc for this case?

[nridge]

Address review comment

clang/include/clang/AST/ExprConcepts.h

static bool classof(const Stmt *T) {
     return T->getStmtClass() == ConceptSpecializationExprClass;
   }
 
   SourceLocation getBeginLoc() const LLVM_READONLY {
     return ConceptName.getBeginLoc();
   }
 
   SourceLocation getEndLoc() const LLVM_READONLY {
-    return ArgsAsWritten->RAngleLoc;
+    // If the ConceptSpecializationExpr is the ImmediatelyDeclaredConstraint
+    // of a TypeConstraint written syntactically as a constrained-parameter,
+    // there may not be a template argument list.
+    return ArgsAsWritten->RAngleLoc.isValid() ? ArgsAsWritten->RAngleLoc
+                                              : ConceptName.getEndLoc();
   }
 
   // Iterators
   child_range children() {
     return child_range(child_iterator(), child_iterator());
   }
   const_child_range children() const {
     return const_child_range(const_child_iterator(), const_child_iterator());

clang/test/AST/ast-dump-concepts.cpp

 // RUN: %clang_cc1 -triple x86_64-unknown-unknown -std=c++2a -ast-dump -ast-dump-filter Foo %s | FileCheck -strict-whitespace %s
 
 // Test with serialization:
 // RUN: %clang_cc1 -std=c++20 -triple x86_64-unknown-unknown -emit-pch -o %t %s
 // RUN: %clang_cc1 -x c++ -std=c++20 -triple x86_64-unknown-unknown -include-pch %t \
 // RUN: -ast-dump-all -ast-dump-filter Foo /dev/null \
 // RUN: | FileCheck --strict-whitespace %s
 
+template <typename T>
+concept unary_concept = true;
+
 template <typename T, typename U>
 concept binary_concept = true;
 
 template <typename T>
 struct Foo {
   // CHECK:      TemplateTypeParmDecl {{.*}} referenced Concept {{.*}} 'binary_concept'
-  // CHECK-NEXT: |-ConceptSpecializationExpr {{.*}} 'bool'
+  // CHECK-NEXT: |-ConceptSpecializationExpr {{.*}} <col:13, col:31> 'bool'
   // CHECK-NEXT: `-TemplateArgument {{.*}} type 'int'
   template <binary_concept<int> R>
   Foo(R);
+
+  // CHECK:      TemplateTypeParmDecl {{.*}} referenced Concept {{.*}} 'unary_concept'
+  // CHECK-NEXT: `-ConceptSpecializationExpr {{.*}} <col:13> 'bool'
+  template <unary_concept R>
+  Foo(R);
 };