[clang] [clang][Sema] Diagnose exceptions only in non-dependent context in discarded `try/catch/throw` blocks (PR #139859)

Wed May 14 06:14:48 PDT 2025

Rajveer100 wrote:

> @Rajveer100 I think instead of looking at the context, we should check if the expression (`Ex`) is instantiation dependent

Checking the expression causes a crash:

<details><summary>Details</summary>
<p>

```shell
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script.
Stack dump:
0.	Program arguments: /Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang -cc1 -internal-isystem /Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/lib/clang/21/include -nostdsysteminc -fsyntax-only -verify -std=c++20 /Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/clang/test/SemaCXX/no-exceptions.cpp
1.	/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/clang/test/SemaCXX/no-exceptions.cpp:24:8: current parser token ';'
2.	/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/clang/test/SemaCXX/no-exceptions.cpp:22:1: parsing namespace 'test1'
3.	/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/clang/test/SemaCXX/no-exceptions.cpp:23:10: parsing function body 'test1::f'
4.	/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/clang/test/SemaCXX/no-exceptions.cpp:23:10: in compound statement ('{}')
 #0 0x000000010954d198 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x10538d198)
 #1 0x000000010954d71c PrintStackTraceSignalHandler(void*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x10538d71c)
 #2 0x000000010954b584 llvm::sys::RunSignalHandlers() (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x10538b584)
 #3 0x000000010954dfe8 SignalHandler(int, __siginfo*, void*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x10538dfe8)
 #4 0x00000001876af624 (/usr/lib/system/libsystem_platform.dylib+0x1804ab624)
 #5 0x000000010a1ef9cc clang::Expr::isInstantiationDependent() const (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x10602f9cc)
 #6 0x000000010d507f54 clang::Sema::BuildCXXThrow(clang::SourceLocation, clang::Expr*, bool) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x109347f54)
 #7 0x000000010d507df0 clang::Sema::ActOnCXXThrow(clang::Scope*, clang::SourceLocation, clang::Expr*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x109347df0)
 #8 0x000000010cd0e954 clang::Parser::ParseThrowExpression() (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108b4e954)
 #9 0x000000010ccec734 clang::Parser::ParseAssignmentExpression(clang::TypeCastState) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108b2c734)
#10 0x000000010ccec620 clang::Parser::ParseExpression(clang::TypeCastState) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108b2c620)
#11 0x000000010cd88a2c clang::Parser::ParseExprStatement(clang::Parser::ParsedStmtContext) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bc8a2c)
#12 0x000000010cd86d74 clang::Parser::ParseStatementOrDeclarationAfterAttributes(llvm::SmallVector<clang::Stmt*, 24u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*, clang::ParsedAttributes&, clang::ParsedAttributes&) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bc6d74)
#13 0x000000010cd865e0 clang::Parser::ParseStatementOrDeclaration(llvm::SmallVector<clang::Stmt*, 24u>&, clang::Parser::ParsedStmtContext, clang::SourceLocation*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bc65e0)
#14 0x000000010cd8f1f8 clang::Parser::ParseCompoundStatementBody(bool) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bcf1f8)
#15 0x000000010cd90914 clang::Parser::ParseFunctionStatementBody(clang::Decl*, clang::Parser::ParseScope&) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bd0914)
#16 0x000000010cdb078c clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bf078c)
#17 0x000000010cc8d06c clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::ParsedAttributes&, clang::Parser::ParsedTemplateInfo&, clang::SourceLocation*, clang::Parser::ForRangeInit*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108acd06c)
#18 0x000000010cdaf884 clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec&, clang::AccessSpecifier) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bef884)
#19 0x000000010cdaee10 clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*, clang::AccessSpecifier) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108beee10)
#20 0x000000010cdae00c clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bee00c)
#21 0x000000010ccbee98 clang::Parser::ParseInnerNamespace(llvm::SmallVector<clang::Parser::InnerNamespaceInfo, 4u> const&, unsigned int, clang::SourceLocation&, clang::ParsedAttributes&, clang::BalancedDelimiterTracker&) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108afee98)
#22 0x000000010ccbe458 clang::Parser::ParseNamespace(clang::DeclaratorContext, clang::SourceLocation&, clang::SourceLocation) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108afe458)
#23 0x000000010cc8baf0 clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributes&, clang::ParsedAttributes&, clang::SourceLocation*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108acbaf0)
#24 0x000000010cdadaf8 clang::Parser::ParseExternalDeclaration(clang::ParsedAttributes&, clang::ParsedAttributes&, clang::ParsingDeclSpec*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bedaf8)
#25 0x000000010cdac010 clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, clang::Sema::ModuleImportState&) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108bec010)
#26 0x000000010cc70f38 clang::ParseAST(clang::Sema&, bool, bool) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x108ab0f38)
#27 0x000000010b0dd6a4 clang::ASTFrontendAction::ExecuteAction() (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x106f1d6a4)
#28 0x000000010b0dcf38 clang::FrontendAction::Execute() (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x106f1cf38)
#29 0x000000010aff394c clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x106e3394c)
#30 0x000000010b21832c clang::ExecuteCompilerInvocation(clang::CompilerInstance*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x10705832c)
#31 0x00000001041d1b34 cc1_main(llvm::ArrayRef<char const*>, char const*, void*) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x100011b34)
#32 0x00000001041c3700 ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&, llvm::ToolContext const&) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x100003700)
#33 0x00000001041c2424 clang_main(int, char**, llvm::ToolContext const&) (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x100002424)
#34 0x00000001041fcf0c main (/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang-21+0x10003cf0c)
#35 0x00000001872d6b4c 
/Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/tools/clang/test/SemaCXX/Output/no-exceptions.cpp.script: line 1: 31304 Segmentation fault: 11  /Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/bin/clang -cc1 -internal-isystem /Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/build/lib/clang/21/include -nostdsysteminc -fsyntax-only -verify -std=c++20 /Users/rajveersingh/GitHub-OpenSource/llvm-project/llvm-project/clang/test/SemaCXX/no-exceptions.cpp

--

********************
********************
Failed Tests (1):
  Clang :: SemaCXX/no-exceptions.cpp

Testing Time: 7.40s

Total Discovered Tests: 1
  Failed: 1 (100.00%)
```

</p>
</details>

> What we will have to do likely is move the checking for this to some piece of common code that is used by TreeTransform for these two. I haven't looked at a good place, but you'll probably see TransformCXXThrowExpr (and an equiv for try) that will call a rebuild/etc type function, which should then call the build (or some variety of a check function).

Also note, even in THOSE cases we have to properly check the decl context, since it could be a partial specialization/instantiation, so please make sure those are tested as well!

I will have a look.

https://github.com/llvm/llvm-project/pull/139859