This is an archive of the discontinued LLVM Phabricator instance.

[clang-tidy] Implement CppCoreGuideline F.54
ClosedPublic

Authored by ccotter on Jan 6 2023, 6:49 AM.

Details

Summary

Warn when a lambda specifies a default capture and captures
`this`. Offer FixIts to correct the code.

Diff Detail

Event Timeline

ccotter created this revision.Jan 6 2023, 6:49 AM
Herald added a project: Restricted Project. · View Herald Transcript
ccotter requested review of this revision.Jan 6 2023, 6:49 AM
Herald added a project: Restricted Project. · View Herald TranscriptJan 6 2023, 6:49 AM
Herald added a subscriber: cfe-commits. · View Herald Transcript
Eugene.Zelenko added inline comments.
clang-tools-extra/docs/ReleaseNotes.rst
118

fix-it.

clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-capture-this-with-capture-default.rst
6 ↗(On Diff #486858)

Please make first statement same as in Release Notes.

ccotter updated this revision to Diff 486873.Jan 6 2023, 7:22 AM
ccotter marked an inline comment as done.
  • docs feedback
ccotter marked an inline comment as done.Jan 6 2023, 7:23 AM
carlosgalvezp added inline comments.Jan 6 2023, 12:37 PM
clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-this-with-capture-default.cpp
10

"default capture"?

10

I find the check name a bit unintuitive. If you are up for a rename (you can use rename_check.py), I would consider renaming to something like cppcoreguidelines-avoid-default-capture-when-capturing-this

Like, what should be avoided is not "capturing this", it's using a default capture.

Would be good to get other reviewers opinion before spending time on renaming.

10

Maybe put it within quotes so clarify it's a C++ keyword? Either backticks this or single quotes 'this' would work I think, unless we have some other convention.

carlosgalvezp added inline comments.Jan 6 2023, 12:39 PM
clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-this-with-capture-default.cpp
2

I believe this is the default, does it make sense to remove it or do we need to be explicit?

ccotter updated this revision to Diff 487081.Jan 7 2023, 4:11 AM
  • Use "capture default" consistently and update diagnostic message
ccotter updated this revision to Diff 487082.Jan 7 2023, 4:11 AM

oops, bad 'arc diff' again

ccotter marked an inline comment as done.Jan 7 2023, 4:20 AM
ccotter added inline comments.
clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-this-with-capture-default.cpp
10

I updated all references to capture default to say "capture default" as this is how it is spelled in the standard. The CppCoreGuideline for F.54 does use "default capture" though, so I'll open an issue seeing if that wording should instead say "capture default." Also for reference, git grep within the llvm-project repo shows

$ git grep -i 'capture default' | wc -l
      43
$ git grep -i 'default capture' | wc -l
      54
$ git grep -i 'capture.default' | wc -l # E.g., 'capture-default' or 'capture default'
     105
10

Updated with a single quote. I didn't find any clang-tidy diagnostics emitting backticks, but saw usage of single quotes when referring to identifiers like variable or class names.

10

+1 - I admit, I struggled naming this check. More feedback welcome on the name

ccotter marked an inline comment as done and an inline comment as not done.Jan 7 2023, 4:48 AM
ccotter added inline comments.
clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-this-with-capture-default.cpp
10

https://github.com/isocpp/CppCoreGuidelines/pull/2016 for "capture default" vs "default capture"

carlosgalvezp added inline comments.Jan 7 2023, 5:36 AM
clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-this-with-capture-default.cpp
10

Interesting, thanks for investigating this! cppreference also uses that terminology.
It sounds quite strange to me since that's not how humans read english text (which is what the diagnostic is meant for). We use "default constructor", "default arguments", etc.

Anyhow this is a minor detail that shouldn't block the patch. Thanks for opening the pull requet towards CppCoreGuidelines!

ccotter added inline comments.Jan 7 2023, 6:10 AM
clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-this-with-capture-default.cpp
10

Since this is a more minor detail, we could probably follow up on the "capture default" wording on the CppCoreGuidelines issue I opened. I'll add that I *just* changed the lone occurrence of "default capture" in https://en.cppreference.com/mwiki/index.php?title=cpp%2Flanguage%2Flambda&diff=146169&oldid=145543, since the other 15 references were phrased "capture default" or "capture-default."

carlosgalvezp added inline comments.Jan 7 2023, 12:52 PM
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureThisWithCaptureDefaultCheck.cpp
35 ↗(On Diff #487084)

Not having being involved in the development of this check I don't quite understand what this error message means, could you provide a more descriptive message?

It's also unclear if the program is supposed to abort when entering this branch, or if it's expected that it returns just fine? If it's supposed to return just fine, I think the check should not print anything, to keep the users' logs clean.

clang-tools-extra/docs/ReleaseNotes.rst
117

This text should also be at the beginning of the check class documentation (in the Check.h, line 18)

clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-capture-this-with-capture-default.rst
9 ↗(On Diff #487084)

defaults

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-this-with-capture-default.cpp
10

Another suggestion for the check name:

"cppcoreguidelines-avoid-capture-default-in-member-functions"

ccotter updated this revision to Diff 487130.Jan 7 2023, 5:22 PM
  • rm trace; tidy docs
ccotter marked 2 inline comments as done.Jan 7 2023, 5:25 PM
ccotter added inline comments.
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureThisWithCaptureDefaultCheck.cpp
35 ↗(On Diff #487084)

My bad - I forgot to remove this trace. Both branches are valid branches for normal program execution.

carlosgalvezp accepted this revision.Jan 8 2023, 7:16 AM

LGTM! Please give a few days for other reviewers to comment. If you are not 100% happy with the check name I'd suggest to change it before merging, it will be much harder to change once it's in.

This revision is now accepted and ready to land.Jan 8 2023, 7:16 AM
Eugene.Zelenko added inline comments.Jan 8 2023, 7:28 AM
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureThisWithCaptureDefaultCheck.cpp
32 ↗(On Diff #487130)

Should be const SourceManager &.

ccotter updated this revision to Diff 487189.Jan 8 2023, 8:07 AM
  • Use const&
ccotter updated this revision to Diff 487193.Jan 8 2023, 8:14 AM
  • rename to avoid-capture-deafult-when-capturing-this
ccotter marked an inline comment as done.Jan 8 2023, 8:15 AM

Thanks!

I opted for 'avoid-capture-default-when-capturing-this' and updated the name and docs etc in the most recent diff.

carlosgalvezp accepted this revision.Jan 8 2023, 8:19 AM

LGTM! Minor nit.

clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-capture-default-when-capturing-this.rst
5

Fix line so it's as long as the text above

ccotter updated this revision to Diff 487195.Jan 8 2023, 8:37 AM
  • tidy up docs
ccotter marked an inline comment as done.Jan 8 2023, 8:37 AM
njames93 requested changes to this revision.Jan 10 2023, 9:23 AM

Can you run this through clang format to make sure the pre merge is happy and address those nits

clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.cpp
81

Would be nice to show if this is implicitly captured.

clang-tools-extra/docs/clang-tidy/checks/cppcoreguidelines/avoid-capture-default-when-capturing-this.rst
6

Not necessary to specify fix behaviour as that's provided in the check list

19

Please fix these examples as this isn't actually captured because the names don't match.

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-this-with-capture-default.cpp
10

Please can you include the whole expected line in the check fix markers, same goes for all tests below

This revision now requires changes to proceed.Jan 10 2023, 9:23 AM
ccotter updated this revision to Diff 488084.Jan 10 2023, 11:00 PM
  • clang-format
  • Show whether 'this' is implicitly captured
  • fix docs
ccotter updated this revision to Diff 488085.Jan 10 2023, 11:06 PM
  • Rename test to match check name
njames93 accepted this revision.Jan 12 2023, 12:01 PM

Just 2 more CHECK-FIXES lines need updating.
FWIW the reason its good to be explicit is because FileCheck will start searching from the line where the previous CHECK-FIXES had and stop when it sees line that contains the match.
In this example:

// CHECK-FIXES: [this]() { };

If the there was an error with the fix, but later on in the file, that string was found. FileCheck would assume the CHECK-FIXES directive was found and report success.
That may in turn lead other CHECK-FIXES to fail due to the position of the previous match. But those error message would be slightly more confusing as the expected fix was actually found in the output file (just not in the correct place)
Expanding the check to this:

// CHECK-FIXES: auto explicit_this_capture = [this]() { };

Means we have to match the whole line(which is a lot less likely to appear again later in the file.)

clang-tools-extra/test/clang-tidy/checkers/cppcoreguidelines/avoid-capture-default-when-capturing-this.cpp
10 ↗(On Diff #488085)
14 ↗(On Diff #488085)
This revision is now accepted and ready to land.Jan 12 2023, 12:01 PM
ccotter updated this revision to Diff 488943.Jan 13 2023, 4:25 AM
  • Finish stengthening CHECK-FIXES
ccotter marked 2 inline comments as done.Jan 13 2023, 4:26 AM

Thanks for pointing that out.

My latest update to the diff was the result of a rebase, then addressing the final comments. What I've been doing is something like

git pull upstream main --rebase
# make more edits
git commit -am ....
arc diff --update D141133 upstream/main

I'm not sure if this is the best way to rebase phabs, but please let me know if there's a better way for phab to understand.

My latest update to the diff was the result of a rebase, then addressing the final comments. What I've been doing is something like

git pull upstream main --rebase
# make more edits
git commit -am ....
arc diff --update D141133 upstream/main

I'm not sure if this is the best way to rebase phabs, but please let me know if there's a better way for phab to understand.

I just run arc diff HEAD~ after rebase, and works just fine :)

ccotter marked 2 inline comments as done.Jan 19 2023, 7:06 PM

Would someone with merge access mind committing this? I double checked and this diff can be applied on the latest upstream/main. Thanks!

Eugene.Zelenko added inline comments.Jan 19 2023, 7:11 PM
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.cpp
2

Ditto.

clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.h
2

Please merge these two lines. Amount of dashes and equal signs could be reduced.

clang-tools-extra/docs/ReleaseNotes.rst
117

The check also offers fix-its. could be omitted. This information presents in check table.

ccotter updated this revision to Diff 490701.Jan 19 2023, 7:21 PM
  • cleanup comments, docs
ccotter marked 3 inline comments as done.Jan 19 2023, 7:23 PM
carlosgalvezp requested changes to this revision.Jan 22 2023, 7:55 AM
carlosgalvezp added inline comments.
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.cpp
20

We recently switched to using C++17 nested namespaces for all the clang-tidy folder, please update to keep it consistent.

This revision now requires changes to proceed.Jan 22 2023, 7:55 AM
ccotter updated this revision to Diff 491165.Jan 22 2023, 8:06 AM
  • Use nested namespace
ccotter marked an inline comment as done.Jan 22 2023, 8:07 AM
ccotter added inline comments.
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.cpp
20

Just curious - I noticed the clang-tidy headers do not use nested namespaces as part of the recent switch. Are the headers slated to be updated too?

carlosgalvezp added inline comments.Jan 22 2023, 8:07 AM
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.h
42–44

Forgot to comment but you'll need it here too :)

carlosgalvezp added inline comments.Jan 22 2023, 8:10 AM
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.cpp
20

Oh crap, I must have missed to add the header-filter option when applying the change, it should apply to headers as well! Will fix in a separate patch.

ccotter updated this revision to Diff 491171.Jan 22 2023, 8:36 AM
ccotter marked an inline comment as done.
  • Use nested namespace in header too;
ccotter marked an inline comment as done.Jan 22 2023, 9:11 AM
carlosgalvezp accepted this revision.Jan 23 2023, 12:47 PM

LGTM, thanks for the contribution! Let's give a couple days for the others to have a last look

This revision is now accepted and ready to land.Jan 23 2023, 12:47 PM

Gentle poke for any last reviews?

carlosgalvezp added inline comments.Jan 30 2023, 2:35 AM
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.cpp
81

Was this comment addressed? I see it marked as "Not Done".

ccotter marked 2 inline comments as done.Jan 30 2023, 6:06 AM
ccotter added inline comments.
clang-tools-extra/clang-tidy/cppcoreguidelines/AvoidCaptureDefaultWhenCapturingThisCheck.cpp
81

oh yes, I forgot to mark addressed.

carlosgalvezp accepted this revision.Jan 30 2023, 7:49 AM

Thanks for updating the comment! Since I marked it as approved last time, I will land this in the next couple of days if no more comments come up.

This revision was automatically updated to reflect the committed changes.