Assertion failure in clangd

[ilovepi]

We're seeing an assertion failure in clangd in Fuchsia code. This code compiles fine, both in release and assert builds, so its a bit surprising. We found this because it was crashing for our developers.

Error :

clangd: /usr/local/google/home/paulkirth/llvm-fork/clang/lib/Serialization/ASTWriterDecl.cpp:1884: void clang::ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *): Assertion `(bool)TC == D->hasTypeConstraint()' failed.\n"

lsp.log

Do we have a guide on how to obtain a reproducer for clangd? is using the preceding compile command to get a preprocessed cpp file sufficient? The Fuchsia build is quite large, and I'm not sure how to provide a nice reproducer that will work w/ clangd.

[llvmbot]

@llvm/issue-subscribers-clangd

Author: Paul Kirth (ilovepi)

We're seeing an assertion failure in `clangd` in Fuchsia code. This code compiles fine, both in release and assert builds, so its a bit surprising. We found this because it was crashing for our developers.

Error :

clangd: /usr/local/google/home/paulkirth/llvm-fork/clang/lib/Serialization/ASTWriterDecl.cpp:1884: void clang::ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *): Assertion `(bool)TC == D->hasTypeConstraint()' failed.\n"

lsp.log

Do we have a guide on how to obtain a reproducer for clangd? is using the preceding compile command to get a preprocessed cpp file sufficient? The Fuchsia build is quite large, and I'm not sure how to provide a nice reproducer that will work w/ clangd.

[HighCommander4]

You can find some tips at https://clangd.llvm.org/troubleshooting#dealing-with-crashes.

See also #99036 for a previous report of the same assertion failure (but unfortunately no reproducer).

[ilovepi]

Thanks. I’ll try to repro when I get to work tomorrow.

[ilovepi]

So assuming that the if I run w/ --background-index=0 -j=1 the proceeding compile command should reproduce the error w/ clang, I'm having trouble reproducing this error using the same build of clang (e.g. Release + asserts). This isn't too surprising, given that we're building this file constantly, but its not clear to me how I can get clangd/clang to run over the source file, so that I can run something like creduce over it.

[HighCommander4]

So assuming that the if I run w/ --background-index=0 -j=1 the proceeding compile command should reproduce the error w/ clang,

It might, but not necessarily; there are some clangd-specific codepaths that clangd runs but clang doesn't, and even the clang codepaths are run in a slightly different way (clangd basically implicitly builds a PCH of the includes at the top of the file, and consumes the PCH while parsing the rest of the file).

If you want a command-line way of running clangd for reduction purposes, clangd --check=source.cpp should do it.

[ilovepi]

hmm, it seems to happen when it can't find one of the include (it compiles, so I'm not sure why it doesn't work w/ clangd). Preprocessing the file seems to bypass the error, so reducing is hard

The first phase of reductions lead to:

#include <a>
#include "chars-from.h"

Where a doesn't exist.

Pasting in the content of "chars-from.h" and reducing that gives

#include <a>
#include <string_veiw>

The thing to note though, is that I'm only able to repro the failure when I copy the reduced file back into the Fuchsia source tree.

#!/bin/bash

DIR=$HOME/fuchsia/out/core.arm64-release
cp $PWD/uart.h $DIR/../../zircon/system/ulib/uart/include/lib/uart/uart.h
cd $DIR
/usr/local/google/home/paulkirth/llvm-fork/build/bin/clangd --compile-commands-dir=$DIR --background-index=0 --clang-tidy --check=../../zircon/system/ulib/uart/include/lib/uart/uart.h

if [ $? -eq 134 ]; then
    exit 0
else
    exit 1
fi

The only config files I'm aware that we use are https://cs.opensource.google/fuchsia/fuchsia/+/main:.clang-format and https://cs.opensource.google/fuchsia/fuchsia/+/main:.clang-tidy

If there's a way to recreate the rest of the context so I can run the same test w/o having to copy things back to the source tree and run the command from the build directory, that'd be great to know/document. I'd be happy to try something else, but I really don't know what to try/how to isolate this.

In case its relevant, I'm including the error output here too:

I[21:53:09.578] Fuchsia clangd version 20.0.0git (git@github.com:ilovepi/llvm-project 1335a11176f99cc54f423fe173708bd2373b59f7)
I[21:53:09.579] Features: linux+debug
I[21:53:09.579] PID: 2115319
I[21:53:09.579] Working directory: /usr/local/google/home/paulkirth/fuchsia/out/core.arm64-release
I[21:53:09.579] argv[0]: /usr/local/google/home/paulkirth/llvm-fork/build/bin/clangd
I[21:53:09.579] argv[1]: --compile-commands-dir=/usr/local/google/home/paulkirth/fuchsia/out/core.arm64-release
I[21:53:09.579] argv[2]: --background-index=0
I[21:53:09.579] argv[3]: --clang-tidy
I[21:53:09.579] argv[4]: --check=../../zircon/system/ulib/uart/include/lib/uart/uart.h
I[21:53:09.579] Entering check mode (no LSP server)
I[21:53:09.579] Testing on source file /usr/local/google/home/paulkirth/fuchsia/zircon/system/ulib/uart/include/lib/uart/uart.h
I[21:53:09.579] Loading compilation database...
I[21:53:10.018] Loaded compilation database from /usr/local/google/home/paulkirth/fuchsia/out/core.arm64-release/compile_commands.json
I[21:53:10.020] Compile command inferred from ../../zircon/system/ulib/uart/test/interrupt-test/uart-interrupt-test.cc is: [/usr/local/google/home/paulkirth/fuchsia/out/core.arm64-release] ../../prebuilt/third_party/clang/linux-x64/bin/clang++ --driver-mode=g++ -MD -MF obj/zircon/system/ulib/uart/test/interrupt-test/uart-interrupt-test.uart-interrupt-test.cc.o.d -DTOOLCHAIN_VERSION=Ej-GgGJgdd4DBjgmGvs5HTjEwhfzJMx2gaUeySSgH84C -D_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D_LIBCPP_REMOVE_TRANSITIVE_INCLUDES -DNDEBUG=1 -D_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS=1 -I../.. -Igen -I../../src/zircon/testing/standalone-test/include -I../../zircon/system/ulib/zx/include -I../../sdk/lib/fit/include -I../../sdk/lib/stdcompat/include -I../../src/zircon/lib/zircon/include -Ifidling/gen/zircon/vdso/zx/zither/legacy_syscall_cdecl -I../../zircon/system/ulib/zxtest/include -I../../zircon/system/ulib/fbl/include -fcolor-diagnostics -fcrash-diagnostics-dir=clang-crashreports -fcrash-diagnostics=all -Wa,--crel,--allow-experimental-crel -ffp-contract=off --sysroot=gen/zircon/public/sysroot/cpp --target=aarch64-unknown-fuchsia -ffuchsia-api-level=4293918720 -march=armv8-a+simd+crc+crypto -mtune=generic -ffile-compilation-dir=. -no-canonical-prefixes -fomit-frame-pointer -fdata-sections -ffunction-sections -Os -mllvm -enable-ml-inliner=release -flto -mllvm -wholeprogramdevirt-branch-funnel-threshold=0 -ffat-lto-objects -Xclang -debug-info-kind=constructor -g3 -grecord-gcc-switches -gdwarf-5 -gz=zstd -Wall -Wextra -Wconversion -Wextra-semi -Wimplicit-fallthrough -Wnewline-eof -Wstrict-prototypes -Wwrite-strings -Wno-sign-conversion -Wno-unused-parameter -Wnonportable-system-include-path -Wno-missing-field-initializers -Wno-extra-qualification -Wno-cast-function-type-strict -Wno-cast-function-type-mismatch -Wno-unknown-warning-option -Wno-missing-template-arg-list-after-template-kw -Wno-deprecated-pragma -fvisibility=hidden -Werror -Wa,--fatal-warnings -Wno-error=deprecated-declarations -ftrivial-auto-var-init=pattern -Wthread-safety -Wno-unknown-warning-option -Wno-thread-safety-reference-return -fvisibility-inlines-hidden -Wno-deprecated-this-capture -fno-exceptions -fno-rtti -ftemplate-backtrace-limit=0 -Wno-unknown-warning-option -Wno-vla-cxx-extension -c -x c++-header -std=c++20 -resource-dir=/usr/local/google/home/paulkirth/llvm-fork/build/lib/clang/20 -- /usr/local/google/home/paulkirth/fuchsia/zircon/system/ulib/uart/include/lib/uart/uart.h
I[21:53:10.020] Parsing command...
I[21:53:10.022] internal (cc1) args are: -cc1 -triple aarch64-unknown-fuchsia -fsyntax-only -disable-free -clear-ast-before-backend -main-file-name uart.h -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=none -ffp-contract=off -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu generic -target-feature +v8a -target-feature +aes -target-feature +crc -target-feature +crypto -target-feature +fp-armv8 -target-feature +neon -target-feature +sha2 -target-feature +fix-cortex-a53-835769 -target-abi aapcs -tune-cpu generic -debug-info-kind=constructor -dwarf-version=5 -debugger-tuning=gdb --compress-debug-sections=zstd -fdebug-compilation-dir=. -mllvm -crash-diagnostics-dir=clang-crashreports -ffunction-sections -fdata-sections -fcoverage-compilation-dir=. -resource-dir /usr/local/google/home/paulkirth/llvm-fork/build/lib/clang/20 -dependency-file obj/zircon/system/ulib/uart/test/interrupt-test/uart-interrupt-test.uart-interrupt-test.cc.o.d -MT uart.o -sys-header-deps -module-file-deps -D TOOLCHAIN_VERSION=Ej-GgGJgdd4DBjgmGvs5HTjEwhfzJMx2gaUeySSgH84C -D _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D _LIBCPP_REMOVE_TRANSITIVE_INCLUDES -D NDEBUG=1 -D _LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS=1 -I ../.. -I gen -I ../../src/zircon/testing/standalone-test/include -I ../../zircon/system/ulib/zx/include -I ../../sdk/lib/fit/include -I ../../sdk/lib/stdcompat/include -I ../../src/zircon/lib/zircon/include -I fidling/gen/zircon/vdso/zx/zither/legacy_syscall_cdecl -I ../../zircon/system/ulib/zxtest/include -I ../../zircon/system/ulib/fbl/include -isysroot gen/zircon/public/sysroot/cpp -internal-isystem ../../prebuilt/third_party/clang/linux-x64/bin/../include/aarch64-unknown-fuchsia/noexcept/c++/v1 -internal-isystem ../../prebuilt/third_party/clang/linux-x64/bin/../include/aarch64-unknown-fuchsia/c++/v1 -internal-isystem ../../prebuilt/third_party/clang/linux-x64/bin/../include/c++/v1 -internal-isystem /usr/local/google/home/paulkirth/llvm-fork/build/lib/clang/20/include -internal-externc-isystem gen/zircon/public/sysroot/cpp/include -Os -Wall -Wextra -Wconversion -Wextra-semi -Wimplicit-fallthrough -Wnewline-eof -Wstrict-prototypes -Wwrite-strings -Wno-sign-conversion -Wno-unused-parameter -Wnonportable-system-include-path -Wno-missing-field-initializers -Wno-extra-qualification -Wno-cast-function-type-strict -Wno-cast-function-type-mismatch -Wno-unknown-warning-option -Wno-missing-template-arg-list-after-template-kw -Wno-deprecated-pragma -Werror -Wno-error=deprecated-declarations -Wthread-safety -Wno-unknown-warning-option -Wno-thread-safety-reference-return -Wno-deprecated-this-capture -Wno-unknown-warning-option -Wno-vla-cxx-extension -ffuchsia-api-level=4293918720 -std=c++20 -fdeprecated-macro -ferror-limit 19 -ftemplate-backtrace-limit=0 -fvisibility=hidden -fvisibility-inlines-hidden -stack-protector 2 -ftrivial-auto-var-init=pattern -fno-rtti -fno-signed-char -fgnuc-version=4.2.1 -fno-implicit-modules -fskip-odr-check-in-gmf -vectorize-loops -vectorize-slp -no-round-trip-args -debug-info-kind=constructor -mllvm -enable-ml-inliner=release -mllvm -wholeprogramdevirt-branch-funnel-threshold=0 -fsanitize=shadow-call-stack -fno-sanitize-memory-param-retval -fno-sanitize-address-use-odr-indicator -dwarf-debug-flags "../../prebuilt/third_party/clang/linux-x64/bin/clang++ -Xclang -no-round-trip-args --driver-mode=g++ -MD -MF obj/zircon/system/ulib/uart/test/interrupt-test/uart-interrupt-test.uart-interrupt-test.cc.o.d -D TOOLCHAIN_VERSION=Ej-GgGJgdd4DBjgmGvs5HTjEwhfzJMx2gaUeySSgH84C -D _LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS -D _LIBCPP_REMOVE_TRANSITIVE_INCLUDES -D NDEBUG=1 -D _LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS=1 -I ../.. -I gen -I ../../src/zircon/testing/standalone-test/include -I ../../zircon/system/ulib/zx/include -I ../../sdk/lib/fit/include -I ../../sdk/lib/stdcompat/include -I ../../src/zircon/lib/zircon/include -I fidling/gen/zircon/vdso/zx/zither/legacy_syscall_cdecl -I ../../zircon/system/ulib/zxtest/include -I ../../zircon/system/ulib/fbl/include -fcolor-diagnostics -fcrash-diagnostics-dir=clang-crashreports -fcrash-diagnostics=all -Wa,--crel,--allow-experimental-crel -ffp-contract=off --sysroot=gen/zircon/public/sysroot/cpp --target=aarch64-unknown-fuchsia -ffuchsia-api-level=4293918720 -march=armv8-a+simd+crc+crypto -mtune=generic -ffile-compilation-dir=. -no-canonical-prefixes -fomit-frame-pointer -fdata-sections -ffunction-sections -Os -mllvm -enable-ml-inliner=release -flto=full -mllvm -wholeprogramdevirt-branch-funnel-threshold=0 -ffat-lto-objects -Xclang -debug-info-kind=constructor -g3 -grecord-command-line -gdwarf-5 -gz=zstd -Wall -Wextra -Wconversion -Wextra-semi -Wimplicit-fallthrough -Wnewline-eof -Wstrict-prototypes -Wwrite-strings -Wno-sign-conversion -Wno-unused-parameter -Wnonportable-system-include-path -Wno-missing-field-initializers -Wno-extra-qualification -Wno-cast-function-type-strict -Wno-cast-function-type-mismatch -Wno-unknown-warning-option -Wno-missing-template-arg-list-after-template-kw -Wno-deprecated-pragma -fvisibility=hidden -Werror -Wa,--fatal-warnings -Wno-error=deprecated-declarations -ftrivial-auto-var-init=pattern -Wthread-safety -Wno-unknown-warning-option -Wno-thread-safety-reference-return -fvisibility-inlines-hidden -Wno-deprecated-this-capture -fno-exceptions -fno-rtti -ftemplate-backtrace-limit=0 -Wno-unknown-warning-option -Wno-vla-cxx-extension -c -x c++-header -std=c++20 -resource-dir /usr/local/google/home/paulkirth/llvm-fork/build/lib/clang/20 -fsyntax-only /usr/local/google/home/paulkirth/fuchsia/zircon/system/ulib/uart/include/lib/uart/uart.h" -flto=full -flto-unit -ffat-lto-objects -ffat-lto-objects -target-feature +outline-atomics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++-header /usr/local/google/home/paulkirth/fuchsia/zircon/system/ulib/uart/include/lib/uart/uart.h
I[21:53:10.022] Building preamble...
clangd: /usr/local/google/home/paulkirth/llvm-fork/clang/lib/Serialization/ASTWriterDecl.cpp:1884: void clang::ASTDeclWriter::VisitTemplateTypeParmDecl(TemplateTypeParmDecl *): Assertion `(bool)TC == D->hasTypeConstraint()' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: /usr/local/google/home/paulkirth/llvm-fork/build/bin/clangd --compile-commands-dir=/usr/local/google/home/paulkirth/fuchsia/out/core.arm64-release --background-index=0 --clang-tidy --check=../../zircon/system/ulib/uart/include/lib/uart/uart.h
1.      <eof> parser at end of file
2.      ../../prebuilt/third_party/clang/linux-x64/bin/../include/c++/v1/__iterator/concepts.h:91:31: serializing 'std::_Tp'
#0 0x00005637761728c8 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) /usr/local/google/home/paulkirth/llvm-fork/llvm/lib/Support/Unix/Signals.inc:723:13
repro.sh: line 6: 2115319 Aborted                 /usr/local/google/home/paulkirth/llvm-fork/build/bin/clangd --compile-commands-dir=$DIR --background-index=0 --clang-tidy --check=../../zircon/system/ulib/uart/include/lib/uart/uart.h

[HighCommander4]

The only config files I'm aware that we use are https://cs.opensource.google/fuchsia/fuchsia/+/main:.clang-format and https://cs.opensource.google/fuchsia/fuchsia/+/main:.clang-tidy

If there's a way to recreate the rest of the context so I can run the same test w/o having to copy things back to the source tree and run the command from the build directory, that'd be great to know/document. I'd be happy to try something else, but I really don't know what to try/how to isolate this.

You may well have checked on this already, but in case not, an important piece of context that comes to mind is the compile command.

Your log says:

Compile command inferred from ../../zircon/system/ulib/uart/test/interrupt-test/uart-interrupt-test.cc [...]

The choice of file to infer the command from (here, uart-interrupt-test.cc) is informed in part by the path of the file being opened.

Perhaps, when the file is outside of the source tree, even though --compile-commands-dir points to the same compilation database, a different entry is chosen (and thus a different command is ultimately used)?

If so, you could control for this by (manually) giving the CDB an entry for the header file itself, with the flags from the crashing command.