[C++17] boost/url, Assertion failed: (isa<To>(Val) && "cast<Ty>() argument of incompatible type!"), function cast, file llvm/include/llvm/Support/Casting.h, line 579.

[DimitryAndric]

As reported in https://bugs.freebsd.org/269067, compiling boost 1.81.0 using clang with assertions enabled, results in an assertion while compiling boost_1_81_0/libs/url/src/src.cpp:

Starting program: /home/dim/ins/llvmorg-15-init-00019-g9d6a6159730/bin/clang -cc1 -triple x86_64-unknown-freebsd14.0 -emit-obj --mrelax-relocations -disable-free -clear-ast-before-backend -main-file-name src.cpp -mrelocation-model pic -pic-level 2 -fhalf-no-semantic-interposition -mframe-pointer=all -relaxed-aliasing -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -mllvm -treat-scalable-fixed-error-as-warning -debugger-tuning=gdb -fcoverage-compilation-dir=/usr0/freebsd/ports/work/usr/ports/devel/boost-libs/work/boost_1_81_0 -D LIBICONV_PLUG -D LIBICONV_PLUG -D LIBICONV_PLUG -D BOOST_ALL_NO_LIB=1 -D BOOST_URL_DYN_LINK=1 -D BOOST_URL_SOURCE -D NDEBUG -O3 -Wall -Wno-inline -std=gnu++17 -fdeprecated-macro -fdebug-compilation-dir=/usr0/freebsd/ports/work/usr/ports/devel/boost-libs/work/boost_1_81_0 -ferror-limit 19 -fvisibility hidden -fvisibility-inlines-hidden -pthread -stack-protector 2 -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -vectorize-loops -vectorize-slp -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ src-ba0416.cpp
Assertion failed: (isa<X>(Val) && "cast<Ty>() argument of incompatible type!"), function cast, file /home/dim/src/llvm/llvm-project/llvm/include/llvm/Support/Casting.h, line 269.

Program received signal SIGABRT, Aborted.
Sent by thr_kill() from pid 88589 and user 1236.
thr_kill () at thr_kill.S:4
4       thr_kill.S: No such file or directory.
(gdb) bt
#0  thr_kill () at thr_kill.S:4
#1  0x0000000806a469c4 in __raise (s=s@entry=6) at /usr/src/lib/libc/gen/raise.c:52
#2  0x0000000806af7779 in abort () at /usr/src/lib/libc/stdlib/abort.c:67
#3  0x0000000806a297a1 in __assert (func=<optimized out>, file=<optimized out>, line=<optimized out>, failedexpr=<optimized out>) at /usr/src/lib/libc/gen/assert.c:51
#4  0x000000000529a5e8 in clang::Sema::BuildDelegatingInitializer(clang::TypeSourceInfo*, clang::Expr*, clang::CXXRecordDecl*) ()
#5  0x0000000005299ec9 in clang::Sema::BuildBaseInitializer(clang::QualType, clang::TypeSourceInfo*, clang::Expr*, clang::CXXRecordDecl*, clang::SourceLocation) ()
#6  0x00000000052988d8 in clang::Sema::BuildMemInitializer(clang::Decl*, clang::Scope*, clang::CXXScopeSpec&, clang::IdentifierInfo*, clang::OpaquePtr<clang::QualType>, clang::DeclSpec const&, clang::SourceLocation, clang::Expr*, clang::SourceLocation) ()
#7  0x000000000529934d in clang::Sema::ActOnMemInitializer(clang::Decl*, clang::Scope*, clang::CXXScopeSpec&, clang::IdentifierInfo*, clang::OpaquePtr<clang::QualType>, clang::DeclSpec const&, clang::SourceLocation, clang::SourceLocation, llvm::ArrayRef<clang::Expr*>, clang::SourceLocation, clang::SourceLocation) ()
#8  0x0000000004f81a04 in clang::Parser::ParseMemInitializer(clang::Decl*) ()
#9  0x0000000004f80e0c in clang::Parser::ParseConstructorInitializer(clang::Decl*) ()
#10 0x0000000004f6540f in clang::Parser::ParseFunctionDefinition(clang::ParsingDeclarator&, clang::Parser::ParsedTemplateInfo const&, clang::Parser::LateParsedAttrList*) ()
#11 0x0000000004f9a164 in clang::Parser::ParseDeclGroup(clang::ParsingDeclSpec&, clang::DeclaratorContext, clang::SourceLocation*, clang::Parser::ForRangeInit*) ()
#12 0x0000000004f645b0 in clang::Parser::ParseDeclOrFunctionDefInternal(clang::ParsedAttributesWithRange&, clang::ParsingDeclSpec&, clang::AccessSpecifier) ()
#13 0x0000000004f64072 in clang::Parser::ParseDeclarationOrFunctionDefinition(clang::ParsedAttributesWithRange&, clang::ParsingDeclSpec*, clang::AccessSpecifier) ()
#14 0x0000000004f629fd in clang::Parser::ParseExternalDeclaration(clang::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) ()
#15 0x0000000004f6f1a1 in clang::Parser::ParseInnerNamespace(llvm::SmallVector<clang::Parser::InnerNamespaceInfo, 4u> const&, unsigned int, clang::SourceLocation&, clang::ParsedAttributes&, clang::BalancedDelimiterTracker&) ()
#16 0x0000000004f6e961 in clang::Parser::ParseNamespace(clang::DeclaratorContext, clang::SourceLocation&, clang::SourceLocation) ()
#17 0x0000000004f935a9 in clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributesWithRange&, clang::SourceLocation*) ()
#18 0x0000000004f6214f in clang::Parser::ParseExternalDeclaration(clang::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) ()
#19 0x0000000004f6f1a1 in clang::Parser::ParseInnerNamespace(llvm::SmallVector<clang::Parser::InnerNamespaceInfo, 4u> const&, unsigned int, clang::SourceLocation&, clang::ParsedAttributes&, clang::BalancedDelimiterTracker&) ()
#20 0x0000000004f6e961 in clang::Parser::ParseNamespace(clang::DeclaratorContext, clang::SourceLocation&, clang::SourceLocation) ()
#21 0x0000000004f935a9 in clang::Parser::ParseDeclaration(clang::DeclaratorContext, clang::SourceLocation&, clang::ParsedAttributesWithRange&, clang::SourceLocation*) ()
#22 0x0000000004f6214f in clang::Parser::ParseExternalDeclaration(clang::ParsedAttributesWithRange&, clang::ParsingDeclSpec*) ()
#23 0x0000000004f60874 in clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<clang::DeclGroupRef>&, bool) ()
#24 0x0000000004f5a78d in clang::ParseAST(clang::Sema&, bool, bool) ()
#25 0x0000000004671fc3 in clang::FrontendAction::Execute() ()
#26 0x00000000045fc869 in clang::CompilerInstance::ExecuteAction(clang::FrontendAction&) ()
#27 0x0000000004723621 in clang::ExecuteCompilerInvocation(clang::CompilerInstance*) ()
#28 0x000000000202682d in cc1_main(llvm::ArrayRef<char const*>, char const*, void*) ()
#29 0x000000000202408a in ExecuteCC1Tool(llvm::SmallVectorImpl<char const*>&) ()
#30 0x0000000002023e12 in main ()

Minimized test case:

// clang -cc1 -triple x86_64-- -S -O0 -std=c++17 boost-url-min.cpp

namespace urls {
struct segments_view {
  segments_view();
};
struct segments_encoded_view {
  operator segments_view();
} __trans_tmp_1;
segments_view::segments_view() : segments_view(__trans_tmp_1) {}
} // namespace urls

This reproduces with both the oldest and the newest versions of clang that I have, so it is a very long standing bug. It is also specifically C++17 related, since using -std=c++11 or -std=c++14 makes the assertion disappear.

[llvmbot]

@llvm/issue-subscribers-c-17

[llvmbot]

@llvm/issue-subscribers-clang-frontend

[shafik]

This looks like a duplicate of: #39319

but the reproducer looks helpful.

[DimitryAndric]

Closing in favor of #39319.