[AST] Fix the CXXFoldExpr source range when parentheses range is invalid.

The CXXFoldExpr's range is invalid if the cxxfoldexpr is formed via the
Concept's TypeContraints (because the parentheses are not written in the
source code). We fallback to use the range from the pattern.

Differential Revision: https://reviews.llvm.org/D85645

Author: hokein

clang/include/clang/AST/ExprCXX.h

@@ -4575,9 +4575,21 @@ class CXXFoldExpr : public Expr {
     return None;
   }
 
-  SourceLocation getBeginLoc() const LLVM_READONLY { return LParenLoc; }
+  SourceLocation getBeginLoc() const LLVM_READONLY {
+    if (LParenLoc.isValid())
+      return LParenLoc;
+    if (isLeftFold())
+      return getEllipsisLoc();
+    return getLHS()->getBeginLoc();
+  }
 
-  SourceLocation getEndLoc() const LLVM_READONLY { return RParenLoc; }
+  SourceLocation getEndLoc() const LLVM_READONLY {
+    if (RParenLoc.isValid())
+      return RParenLoc;
+    if (isRightFold())
+      return getEllipsisLoc();
+    return getRHS()->getEndLoc();
+  }
 
   static bool classof(const Stmt *T) {
     return T->getStmtClass() == CXXFoldExprClass;

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

@@ -12,6 +12,9 @@ concept unary_concept = true;
 template <typename T, typename U>
 concept binary_concept = true;
 
+template <typename... Ts>
+concept variadic_concept = true;
+
 template <typename T>
 struct Foo {
   // CHECK:      TemplateTypeParmDecl {{.*}} referenced Concept {{.*}} 'binary_concept'
@@ -37,4 +40,12 @@ struct Foo {
   template <typename R>
   Foo(R, char) requires unary_concept<R> {
   }
+
+  // CHECK: CXXFoldExpr {{.*}} <col:13, col:29>
+  template <variadic_concept... Ts>
+  Foo();
+
+  // CHECK: CXXFoldExpr {{.*}} <col:13, col:34>
+  template <variadic_concept<int>... Ts>
+  Foo();
 };