[PATCH] D133555: [pseudo] Eliminate a false parse of the template parameter "class T".

[Haojian Wu via Phabricator via cfe-commits]

hokein created this revision.
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Herald added a subscriber: alextsao1999.
Herald added a project: clang-tools-extra.

Implements the temp.param#2 <https://eel.is/c++draft/temp.param#2> rule with the guard.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D133555

Files:
  clang-tools-extra/pseudo/lib/cxx/CXX.cpp
  clang-tools-extra/pseudo/lib/cxx/cxx.bnf
  clang-tools-extra/pseudo/test/cxx/type-template-parameter.cpp


Index: clang-tools-extra/pseudo/test/cxx/type-template-parameter.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/pseudo/test/cxx/type-template-parameter.cpp
@@ -0,0 +1,9 @@
+// RUN: clang-pseudo -grammar=cxx -source=%s --print-forest | FileCheck %s
+
+// Verify that we don't misparse the "class abc" as an unnamed non-type template-parameter of class T.
+template<class abc>
+struct Foo {};
+
+// CHECK:      template-parameter-list~type-parameter := type-parameter-key IDENTIFIER
+// CHECK-NEXT: ├─type-parameter-key~CLASS :=
+// CHECK-NEXT: └─IDENTIFIER :=
Index: clang-tools-extra/pseudo/lib/cxx/cxx.bnf
===================================================================
--- clang-tools-extra/pseudo/lib/cxx/cxx.bnf
+++ clang-tools-extra/pseudo/lib/cxx/cxx.bnf
@@ -663,7 +663,7 @@
 constraint-logical-and-expression := primary-expression
 constraint-logical-and-expression := constraint-logical-and-expression && primary-expression
 template-parameter := type-parameter
-template-parameter := parameter-declaration
+template-parameter := parameter-declaration [guard]
 type-parameter := type-parameter-key ..._opt IDENTIFIER_opt
 type-parameter := type-parameter-key IDENTIFIER_opt = type-id
 type-parameter := type-constraint ..._opt IDENTIFIER_opt
Index: clang-tools-extra/pseudo/lib/cxx/CXX.cpp
===================================================================
--- clang-tools-extra/pseudo/lib/cxx/CXX.cpp
+++ clang-tools-extra/pseudo/lib/cxx/CXX.cpp
@@ -13,6 +13,7 @@
 #include "clang-pseudo/grammar/LRTable.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/TokenKinds.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Debug.h"
 #include <utility>
@@ -182,6 +183,25 @@
   return true;
 }
 
+bool isNotClassIdentifierFormTemplateParameter(
+    const GuardParams &TemplateParameter) {
+  const ForestNode *ParameterDeclaration = TemplateParameter.RHS[0];
+  assert(ParameterDeclaration->symbol() == cxx::Symbol::parameter_declaration);
+  llvm::SmallVector<clang::tok::TokenKind, 2> Tokens;
+  // FIXME: This is an awkward way to get the end of the covered token range,
+  // pass it in the GuardParams?
+  Token::Index Start = ParameterDeclaration->startTokenIndex();
+  if (TemplateParameter.Tokens.tokens()[Start].Kind != clang::tok::kw_class)
+    return true;
+  Token::Index Last = Start;
+  for (auto &Child : ParameterDeclaration->descendants()) {
+    if (Child.kind() == ForestNode::Terminal)
+      Last = std::max(Last, Child.startTokenIndex());
+  }
+  return !(Last - Start == 1 && TemplateParameter.Tokens.tokens()[Last].Kind ==
+                                    clang::tok::identifier);
+}
+
 // Whether this e.g. decl-specifier contains an "exclusive" type such as a class
 // name, and thus can't combine with a second exclusive type.
 //
@@ -353,6 +373,17 @@
            decl_specifier_seq__L_SQUARE__identifier_list__R_SQUARE__initializer__SEMI,
        specifiesStructuredBinding},
 
+      // C++ [temp.param#2]:
+      //   ...A template-parameter of the form class identifier is a type-parameter.
+      //
+      //   template<class T, T i> void f(T t);
+      // Here, the template f has a type-parameter called T, rather than an
+      // unnamed non-type template-parameter of class T.
+      {
+        rule::template_parameter::parameter_declaration,
+        isNotClassIdentifierFormTemplateParameter,
+      },
+
       // The grammar distinguishes (only) user-defined vs plain string literals,
       // where the clang lexer distinguishes (only) encoding types.
       {rule::user_defined_string_literal_chunk::STRING_LITERAL,


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