[PATCH] D132260: [pseudo] Eliminate a false parse of structured binding declaration.

[Haojian Wu via Phabricator via cfe-commits]

hokein created this revision.
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Using the guard to implement part of the rule https://eel.is/c++draft/dcl.pre#6.

  void foo() {
    // can be parsed as
    //   - structured-binding declaration (a false parse)
    //   - assignment expression
    array[index] = value;
  }


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D132260

Files:
  clang-tools-extra/pseudo/lib/cxx/CXX.cpp
  clang-tools-extra/pseudo/lib/cxx/cxx.bnf
  clang-tools-extra/pseudo/test/cxx/structured-binding.cpp


Index: clang-tools-extra/pseudo/test/cxx/structured-binding.cpp
===================================================================
--- /dev/null
+++ clang-tools-extra/pseudo/test/cxx/structured-binding.cpp
@@ -0,0 +1,7 @@
+
+// RUN: clang-pseudo -grammar=cxx -source=%s --start-symbol=statement-seq --print-forest | FileCheck %s
+
+// Verify there is no false parse of the structured binding declaration.
+ABC[post] = abc;
+// CHECK: statement-seq~expression-statement := expression ;
+// CHECK: postfix-expression [ expr-or-braced-init-list ]
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
@@ -330,7 +330,7 @@
 nodeclspec-function-declaration := function-declarator ;
 alias-declaration := USING IDENTIFIER = defining-type-id ;
 simple-declaration := decl-specifier-seq init-declarator-list_opt ;
-simple-declaration := decl-specifier-seq ref-qualifier_opt [ identifier-list ] initializer ;
+simple-declaration := decl-specifier-seq ref-qualifier_opt [ identifier-list ] initializer ; [guard]
 static_assert-declaration := STATIC_ASSERT ( constant-expression ) ;
 static_assert-declaration := STATIC_ASSERT ( constant-expression , string-literal ) ;
 empty-declaration := ;
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
@@ -161,6 +161,26 @@
   return symbolToToken(P.Lookahead) != tok::kw_else;
 }
 
+bool isStructuredBinding(const ForestNode* N) {
+  assert(N->symbol() == Symbol::decl_specifier_seq);
+  for (const auto &Child : N->descendants()) {
+    if (Child.kind() == ForestNode::Terminal) {
+      auto Kind = symbolToToken(Child.symbol());
+      switch (Kind) {
+      case clang::tok::kw_static:
+      case clang::tok::kw_thread_local:
+      case clang::tok::kw_auto:
+      case clang::tok::kw_const:
+      case clang::tok::kw_volatile:
+        break;
+      default:
+        return false;
+      }
+    }
+  }
+  return true;
+}
+
 // 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.
 //
@@ -320,6 +340,18 @@
       {rule::nested_name_specifier::COLONCOLON,
        TOKEN_GUARD(coloncolon, Tok.prev().Kind != tok::identifier)},
 
+      // Implement C++ [dcl.pre#6]:
+      //   A simple-declaration with an identifier-list is called a structured
+      //   binding declaration ([dcl.struct.bind]). If the decl-specifier-seq
+      //   contains any decl-specifier other than static, thread_­local, auto,
+      //   or cv-qualifiers, the program is ill-formed.
+      {rule::simple_declaration::
+           decl_specifier_seq__ref_qualifier__L_SQUARE__identifier_list__R_SQUARE__initializer__SEMI,
+       GUARD(isStructuredBinding(P.RHS[0]))},
+      {rule::simple_declaration::
+           decl_specifier_seq__L_SQUARE__identifier_list__R_SQUARE__initializer__SEMI,
+       GUARD(isStructuredBinding(P.RHS[0]))},
+
       // 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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