[clangd-dev] additional TextEdits on code completion

Theodore Dubois via clangd-dev clangd-dev at lists.llvm.org
Mon Apr 8 07:29:24 PDT 2019

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.


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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