[clang-repl] Ensure clang-repl accepts all C keywords supported in all language models

[anutosh491]

As can be seen through the docs (https://github.com/llvm/llvm-project/blob/7e1fa09ce2a228c949ce4490c98f2c73ed8ada00/clang/docs/LanguageExtensions.rst#c-keywords-supported-in-all-language-modes), Clang supports certain C keywords in all language modes — this patch ensures clang-repl handles them consistently.

Here's an example testing all the above keywords. We have everything in place except _Imaginary (_Complex works but _Imaginary doesn't which was weird) and _Noreturn

[llvmbot]

@llvm/pr-subscribers-clang

Author: Anutosh Bhat (anutosh491)

Changes

As can be seen through the docs (https://github.com/llvm/llvm-project/blob/7e1fa09ce2a228c949ce4490c98f2c73ed8ada00/clang/docs/LanguageExtensions.rst#c-keywords-supported-in-all-language-modes), Clang supports certain C keywords in all language modes — this patch ensures clang-repl handles them consistently.

Here's an example testing all the above keywords. We have everything in place except _Imaginary (_Complex works but _Imaginary doesn't which was weird) and _Noreturn

---

Full diff: https://github.com/llvm/llvm-project/pull/142749.diff

1 Files Affected:

• (modified) clang/lib/Parse/ParseTentative.cpp (+2)

diff --git a/clang/lib/Parse/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
index 95cee824c40b7..f50bcd8ea90bb 100644
--- a/clang/lib/Parse/ParseTentative.cpp
+++ b/clang/lib/Parse/ParseTentative.cpp
@@ -1171,6 +1171,7 @@ Parser::isCXXDeclarationSpecifier(ImplicitTypenameContext AllowImplicitTypename,
   case tok::kw_inline:
   case tok::kw_virtual:
   case tok::kw_explicit:
+  case tok::kw__Noreturn:
 
     // Modules
   case tok::kw___module_private__:
@@ -1225,6 +1226,7 @@ Parser::isCXXDeclarationSpecifier(ImplicitTypenameContext AllowImplicitTypename,
     // GNU
   case tok::kw_restrict:
   case tok::kw__Complex:
+  case tok::kw__Imaginary:
   case tok::kw___attribute:
   case tok::kw___auto_type:
     return TPResult::True;

[anutosh491]

On Main

anutosh491@vv-nuc:/build/anutosh491/llvm-project/build/bin$ ./clang-repl
clang-repl> _Alignas(16) int x;
clang-repl> int align = _Alignof(double);
clang-repl> _Atomic int atomic_var = 0;
clang-repl> _Complex double complex_val = 1.0 + 2.0i;
clang-repl> _Float16 f = 1.5;
clang-repl> _Thread_local int counter = 0;
clang-repl> _Static_assert(sizeof(int) == 4, "int must be 4 bytes");
clang-repl> _Imaginary float i = 2.0f;
In file included from <<< inputs >>>:1:
input_line_8:1:1: error: expected expression
    1 | _Imaginary float i = 2.0f;
      | ^
error: Parsing failed.
clang-repl> _Noreturn void die() {    while (true) {}}
input_line_9:1:1: error: expected expression
    1 | _Noreturn void die() {    while (true) {}}
      | ^
error: Parsing failed.

On Branch after the change

anutosh491@vv-nuc:/build/anutosh491/llvm-project/build/bin$ ./clang-repl
clang-repl> _Alignas(16) int x;
clang-repl> int align = _Alignof(double);
clang-repl> _Atomic int atomic_var = 0;
clang-repl> _Complex double complex_val = 1.0 + 2.0i;
clang-repl> _Float16 f = 1.5;
clang-repl> _Thread_local int counter = 0;
clang-repl> _Static_assert(sizeof(int) == 4, "int must be 4 bytes");
clang-repl> _Imaginary float i = 2.0f;
In file included from <<< inputs >>>:1:
input_line_8:1:1: error: imaginary types are not supported
    1 | _Imaginary float i = 2.0f;
      | ^
error: Parsing failed.
clang-repl> _Noreturn void die() {    while (true) {}}

This now works how clang would expect it to. For eg

(xeus-cpp) anutosh491@Anutoshs-MacBook-Air xeus-cpp % cat test-file.cpp 
_Imaginary float i = 2.0f;%                                                                                                                                                                                               
(xeus-cpp) anutosh491@Anutoshs-MacBook-Air xeus-cpp % clang++ -std=c++20 test-file.cpp -o test_program 
test-file.cpp:1:1: error: imaginary types are not supported
_Imaginary float i = 2.0f;
^
1 error generated.

And anything with _Noreturn would just compile fine.

[anutosh491]

The error comes from here to be precise

llvm-project/clang/lib/Parse/Parser.cpp

Lines 1026 to 1028 in 41841e6

	if (getLangOpts().IncrementalExtensions &&
	!isDeclarationStatement(/*DisambiguatingWithExpression=*/true))
	return ParseTopLevelStmtDecl();

IsDeclarationStatement should be true but returns false enabling a faulty call to ParseTopLevelStmtDecl

These are also a part of isDeclarationSpecifier (hence -Xcc -xc worked ig)

llvm-project/clang/include/clang/Parse/Parser.h

Lines 7579 to 7583 in 9ba332f

	bool isDeclarationStatement(bool DisambiguatingWithExpression = false) {
	if (getLangOpts().CPlusPlus)
	return isCXXDeclarationStatement(DisambiguatingWithExpression);
	return isDeclarationSpecifier(ImplicitTypenameContext::No, true);
	}

llvm-project/clang/lib/Parse/ParseDecl.cpp

Line 5811 in 2c4f677

case tok::kw__Imaginary:

llvm-project/clang/lib/Parse/ParseDecl.cpp

Line 5856 in 2c4f677

case tok::kw__Noreturn:

[anutosh491]

Should help us in the long run and fix the errors we see while including input/output based header on xeus-cpp-lite (happens cause these internally reference _Noreturn that clang-repl currently fails to understand)

[vgvassilev]

Can you add tests?

[anutosh491]

Can you add tests?

Done.

[vgvassilev]

Lgtm!

[anutosh491]

/cherry-pick 7ca7bcb

[llvmbot]

/pull-request #142909