[clangd-dev] additional TextEdits on code completion

Theodore Dubois via clangd-dev clangd-dev at lists.llvm.org
Mon Apr 8 13:52:36 PDT 2019

It's LanguageClient-neovim. I've also run into a clangd assertion
failure when using that plugin that I haven't seen in VSCode (reported
at https://bugs.llvm.org/show_bug.cgi?id=41091).


On Mon, Apr 8, 2019 at 7:35 AM Sam McCall <sammccall at google.com> wrote:
> On Mon, Apr 8, 2019 at 4:29 PM Theodore Dubois <tbodt at google.com> wrote:
>> I would appreciate a compiler option to entirely disable this feature.
>> I agree with the include-what-you-use style, but my LSP editor plugin
>> has a bug where when a new line is inserted at the top of the file,
>> the cursor stays on the same line number, so it moves up a line.
> Ouch :-( Which editor/plugin is that?
> That makes sense, we need to never insert includes during code completion in that case, and a flag is a reasonable way to configure it (it's not codebase-specific at all).
> Clangd also adds include-insertion fixes to "unknown symbol" diagnostics, so you can still get assistance with #includes that way. (This didn't make the cut for clangd 8 though).
>> ~Theodore
>> On Mon, Apr 8, 2019 at 1:05 AM Sam McCall via clangd-dev
>> <clangd-dev at lists.llvm.org> wrote:
>> >
>> > On Mon, Apr 8, 2019 at 8:36 AM Aneesh Kumar K.V <aneesh.kumar at linux.ibm.com> wrote:
>> >>
>> >> Sam McCall <sammccall at google.com> writes:
>> >>
>> >> > Sorry about that :-( +Eric Liu <ioeric at google.com> who may have thoughts.
>> >> > I don't think we have an option to disable includes today, maybe we should
>> >> > add one...
>> >> >
>> >> > But we don't expect the inserted includes to create compile errors - *this
>> >> > is probably a bug, it'd be great if you could provide more details* (is it
>> >> > the right header but spelled wrong, or the wrong header entirely, etc). It
>> >> > may be that you'd like this feature if it worked properly.
>> >> >
>> >>
>> >> Sorry for the delay in response. This mostly is due to the location where
>> >> the #include line is added. With company-lsp (emacs), it gets added at
>> >> the beginning of the file and the dependency across headers results in
>> >> build failures.
>> >
>> > If you have time, it'd be great to see a breakdown of such an example (which files and symbols are involved, how the compile error comes about).
>> >
>> > Currently we're assuming:
>> > 1) each symbol has a single header where its "main" declaration is found
>> > 2) if you're using a symbol in a file, that header should be included (or the symbol should be forward-declared)
>> > 3) it's safe and useful to directly include exactly the directly required headers, rather than relying on transitive includes
>> > This style is called include-what-you-use. Its main advantages: it tends not to break code when #include structure changes, and it's easy to decide what should be #included.
>> >
>> > Personally, my advice would be to follow this style. If inserting an #include header breaks your compile, it's likely that:
>> >  - that header is not #including one of its dependencies
>> >  - you have a circular dependency, which can be resolved with a forward declaration
>> >  - header guards are missing somewhere
>> > etc
>> >
>> > However I do think it might make sense to offer a way to disable include insertion entirely for projects that are not IWYU-style and don't want to be.
>> >
>> > I do have a pending patch to never insert #includes of files that don't have recognized header guards (#ifdef/#define/#endif). https://reviews.llvm.org/D60316
>> > This avoids triggering the feature in *some* cases where it's not safe.
>> > Happy to look at other heuristics if they're feasible to implement.
>> >
>> >> One important thing to note is, I am able to build without any
>> >> error even without the new #include line. Hence not sure why we should add the
>> >> extra #include when completing function names.
>> >
>> > 1) Often the relevant header is *transitively* included already, but not directly included. If file A needs symbol C, relying on a transitive A.c -> B.h -> C.h include means that if B stops depending on C, or A stops depending on B, then A will break.
>> > 2) There are lots of possible behaviors here and they all have downsides, we have to pick one (at least as default).
>> >   a) never inserting headers: breaks code after many completions
>> >   b) inserting only when the symbol isn't declared in a transitively included header: unacceptable performance penalty to deserialize all declarations from the preamble, problems with incomplete types
>> >   c) inserting only when the primary header isn't transitively included: unpredictable behavior in large codebases, still can break compiles in the same way
>> >   d) IWYU: causes problems in codebases that are not IWYU-clean.
>> >
>> > Cheers, Sam
>> >
>> >>
>> >>
>> >> -aneesh
>> >>
>> > _______________________________________________
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>> > clangd-dev at lists.llvm.org
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