[cfe-dev] clangd, completion in header files

Sam McCall via cfe-dev cfe-dev at lists.llvm.org
Fri Apr 27 00:52:47 PDT 2018

Ah, this is a fun case... logs from a debug clangd with

interpolate: chose ../../third_party/freetype/*src/src/base*/ftbase.c as
proxy for /usr/local/google/home/sammccall/src/chromium/*src/base*/no_destructor.h
preferring none score=3

The trick is the good match between src/src/base and src/base yields 3
points (should probably be two) - clangd doesn't know that "src" is
semantically meaningless, and "base" is at least ambiguous.

This yields at least a few few possible approaches:
1. just fix the scorer to award 2 points instead of 3, which will make this
rarer (should happen in any case)
2. blacklist words like "src" from getting points
3. dynamically detect which words are significant at startup time based on
4. more substantially change the approach to path matching

I quite like the idea of 3, we could index the N rarest directory segments
for each command, rather than the N last.

On Wed, Apr 25, 2018 at 4:34 PM Christian Dullweber <dullweber at chromium.org>

> Hi,
> thanks for implementing the heuristics. Header files that have a cc file
> with the same name are working great now :)
> I found a few issues that I can't really explain. It looks like some
> header-only files are matched with a basically random file:
> base/no_destructor.h, base/macros.h and base/callback_forward.h are
> compiled with commands for third_party/freetype/freetype_source/ftbase.c.
> (according to the "-MF
> obj/third_party/freetype/freetype_source/ftbase.o.d" parameter)
> components/content_settings/core/browser/user_modifiable_provider.h is
> compiled with commands for
> components/autofill/core/browser/browser/address.cc
> There are much better matches such as base/callback_helpers.cc or
> components/content_settings/core/browser/website_settings_info.cc.
> There are also headers where good commands are choosen, e.g.
> components/browsing_data/core/clear_browsing_data_tab.h with
> components/browsing_data/core/core/browsing_data_utils.cc, so I wonder what
> is going wrong with the others files?
> I'm using the clangd build 20180424.RC0-1
> On Thu, Mar 29, 2018 at 4:59 PM Sam McCall <sammccall at google.com> wrote:
>> On Thu, Mar 29, 2018 at 11:34 AM Christian Dullweber <
>> dullweber at chromium.org> wrote:
>>> Sound great, thanks!
>>> One interesting case in Chromium might be generated jni headers. I would
>>> be interested what the heuristic finds for these files:
>>> src/out/Android/gen/chrome/browser/jni_headers/chrome/jni/BrowsingDataBridge_jni.h
>> Indeed, it doesn't do well here, but still compiles fine - this seems to
>> be the case when the exact flags used don't matter much as long as the
>> general project setup is right. Probably quite common in generated files -
>> I guess these tend to have relatively few predictable dependencies, and
>> might prefer unwieldy fully-qualified include paths where a human would add
>> a -I entry. This one includes <jni.h>
>> and "../../../../../../../../base/android/jni_generator/jni_generator_helper.h".
>> The heuristic fares poorly here because the filename is unique, the last
>> few path components (chrome, jni, jni_headers) are unhelpful in locating
>> related cc files, and the "nearby in the tree" logic doesn't handle the
>> separate root for genfiles well.
>> The right file turns out to be e.g.
>> "chrome/browser/android/browsing_data/browsing_data_bridge.cc". The only
>> useful hints here are chrome/browser (not very specific) and
>> BrowsingDataBridge if we used fuzzy word matching to account for case
>> differences. I'm inclined not to try to solve this case without more data.
>> The only diagnostics produced are a bunch of "internal linkage... but not
>> defined" where the header forward declares static functions whose
>> implementations are meant to be provided by the including CC file.
>> This is an artifact of assuming the .h file is standalone, and it seems
>> like a form of non-modularity, but this is a minor issue we can deal with
>> in a few ways and unrelated to the choice of flags.
>> Relevant logs are:
>> Chose
>> /usr/local/google/home/sammccall/src/chromium/src/out/Android/gen/chrome/browser/android/proto/
>> client_discourse_context.pb.cc as proxy for
>> /usr/local/google/home/sammccall/src/chromium/src/out/Android/gen/chrome/browser/jni_headers/chrome/jni/BrowsingDataBridge_jni.h
>> Rebuilding file
>> /usr/local/google/home/sammccall/src/chromium/src/out/Android/gen/chrome/browser/jni_headers/chrome/jni/BrowsingDataBridge_jni.h
>> with command
>> [/usr/local/google/home/sammccall/src/chromium/src/out/Android]
>> ../../third_party/llvm-build/Release+Asserts/bin/clang++ -x c++ -MMD -MF
>> obj/chrome/browser/client_discourse_context_proto/client_discourse_context.pb.o.d
>> ../../third_party/protobuf/src -I gen/protoc_out -I
>> ../../third_party/protobuf/src -fno-strict-aliasing --param
>> ssp-buffer-size=4 -fstack-protector -Wno-builtin-macro-redefined -D
>> __DATE__= -D __TIME__= -D __TIMESTAMP__= -funwind-tables -fPIC -pipe
>> -fcolor-diagnostics -no-canonical-prefixes -ffunction-sections
>> -fno-short-enums --target=arm-linux-androideabi -isystem
>> ../../third_party/android_ndk/sysroot/usr/include/arm-linux-androideabi -D
>> __ANDROID_API__=16 -D __NDK_FPABI__= -D
>> HAVE_PTHREAD_COND_TIMEDWAIT_MONOTONIC=1 -march=armv7-a -mfloat-abi=softfp
>> -mtune=generic-armv7-a -mfpu=neon -mthumb -Wall -Werror -Wextra
>> -Wimplicit-fallthrough -Wthread-safety -Wno-missing-field-initializers
>> -Wno-unused-parameter -Wno-c++11-narrowing -Wno-covered-switch-default
>> -Wno-unneeded-internal-declaration -Wno-inconsistent-missing-override
>> -Wno-undefined-var-template -Wno-nonportable-include-path
>> -Wno-address-of-packed-member -Wno-unused-lambda-capture
>> -Wno-user-defined-warnings -Wno-enum-compare-switch
>> -Wno-null-pointer-arithmetic -Wno-ignored-pragma-optimize -Oz -fno-ident
>> -fdata-sections -ffunction-sections -fomit-frame-pointer -gdwarf-3 -g2
>> -ggnu-pubnames -fvisibility=hidden -Xclang -load -Xclang
>> ../../third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so
>> -Xclang -add-plugin -Xclang find-bad-constructs -Xclang
>> -plugin-arg-find-bad-constructs -Xclang check-ipc -Wheader-hygiene
>> -Wstring-conversion -Wtautological-overlap-compare
>> -Wno-undefined-bool-conversion -Wno-tautological-undefined-compare
>> -std=gnu++14 -fno-exceptions -fno-rtti -isystem
>> ../../third_party/android_ndk/sources/cxx-stl/llvm-libc++/include -isystem
>> ../../third_party/android_ndk/sources/cxx-stl/llvm-libc++abi/include
>> -isystem ../../third_party/android_ndk/sources/android/support/include
>> --sysroot=../../third_party/android_ndk/sysroot -fvisibility-inlines-hidden
>> -c
>> /usr/local/google/home/sammccall/src/chromium/src/out/Android/gen/chrome/browser/jni_headers/chrome/jni/BrowsingDataBridge_jni.h
>> -resource-dir=/usr/local/google/home/sammccall/llvmbuild/bin/../lib/clang/7.0.0
>> (Yes, the -M flags should really be filtered)
>>> the implementation is in:
>>> src/chrome/browser/android/browsing_data/browsing_data_bridge.cc
>>> I don't think that will get matched.
>>> I don't really care if code completion works in generated files but at
>>> least there shouldn't be incorrect error messages in vscode. Is it possible
>>> to exclude a folder from being analyzed by clangd?
>> Not currently, it'll look at anything with a supported extension.
>> It's not obvious to me how to manage either heuristically or via
>> configuration in a way that's easy to use, so unless people have ideas I'd
>> punt on this and try to improve the results instead.
>>> On Thu, Mar 29, 2018 at 1:50 AM, Sam McCall <sammccall at google.com>
>>> wrote:
>>>> Looks like our mail crossed :)
>>>> Cquery's success with this is another point in favor.
>>>> I have a prototype in https://reviews.llvm.org/D45006 (+ 2-line patch
>>>> to enable in clangd: https://reviews.llvm.org/D45007).
>>>> It seems to work pretty well at first glance, but it needs rigorous
>>>> testing. If anyone's feeling this pain, feel free to try it out!
>>>> It does a little bit of indexing to avoid traversing all the entries
>>>> every time, not sure if that's worth it.
>>>> On Wed, Mar 28, 2018 at 9:58 PM Fāng-ruì Sòng via cfe-dev <
>>>> cfe-dev at lists.llvm.org> wrote:
>>>>> Another heuristic solution:
>>>>> Enumerate all compilation database entries and calculate the matching
>>>>> score for each entry with the target file
>>>>> Bonus for common leading components
>>>>> Penalty for diverged path components
>>>>> Bonus for common trailing characters sans filename extension (e.g.
>>>>> Match.cc Match.h are the same sans extension)
>>>>> This heuristic is used in cquery.
>>>>> Add another point for textDocument/didOpen on an unseen filename:
>>>>> The inferred command line options are not authoritative, they should
>>>>> be overriden by other translation units when later it turns out the header
>>>>> file is included by some entry in the compilation database.
>>>>> On Wed, Mar 28, 2018 at 7:12 AM Christian Dullweber via cfe-dev <
>>>>> cfe-dev at lists.llvm.org> wrote:
>>>>>> Hi,
>>>>>> I recently tried to use clangd for Chromium in vscode and hit the
>>>>>> same issue.
>>>>>> I experimented a bit with generating a compile_commands.json file
>>>>>> with valid rules for headers and came to this solution:
>>>>>> https://gist.github.com/xchrdw/bfd2b3a5f765f4195a55d6351daf1b48
>>>>>> I sorted all .cc filenames and then looked up the index of the
>>>>>> closest match for each header using binary search. As there were
>>>>>> some edge cases like the first or last file in a directory, I additionally
>>>>>> compared which file at the index has the largest prefix with the header.
>>>>>> I found a few issues with system headers and some generated protobuf
>>>>>> headers but otherwise it works well.
>>>>>> Native support from clangd would be amazing :)
>>>>>> Thanks,
>>>>>> Christian
>>>>>> _______________________________________________
>>>>>> cfe-dev mailing list
>>>>>> cfe-dev at lists.llvm.org
>>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
>>>>> --
>>>>> 宋方睿
>>>>> _______________________________________________
>>>>> cfe-dev mailing list
>>>>> cfe-dev at lists.llvm.org
>>>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev
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