[clangd] Recognize "don't include me directly" pattern, and suppress include insertion.

[sammccall]

Summary

Typically used with umbrella headers, e.g. GTK:

#if !defined (GTK_H_INSIDE) && !defined (GTK_COMPILATION)
#error "Only <gtk/gtk.h> can be included directly."
#endif

Heuristic is fairly conservative, a quick code search over github showed
a fair number of hits and few/no false positives. (Not all were umbrella
headers, but I'd be happy avoiding include insertion for all of them).

We may want to relax the heuristic later to catch more cases.

[sammccall]

unconfusing my git repo

[sammccall]

remove leftover debugging

[sammccall]

clangd/index/SymbolCollector.cpp

602

this function has been moved to a member so it can call isSelfContainedHeader which is now a member.

Apart from no longer having to change so many params, it is unmodified.

631

this has been moved to a member so it can use the cache and the (non-threadsafe) regex, and its logic has obviously been changed.

[ioeric]

lgtm

clangd/index/SymbolCollector.cpp

631

"self-contained header" doesn't sound accurate anymore. Maybe something like isIncludable?

clangd/index/SymbolCollector.h

125

DontIncludeMePattern or DontIncludeMeRegex?

[sammccall]

DontIncludeMePattern

[sammccall]

clangd/index/SymbolCollector.cpp

631

Let me explain how I think about it, and then I'll change the name if you still don't think it fits.

What we're detecting here (usually) is that this header can't be included unless a certain symbol/state is defined first from the outside.
Whether that's for some direct technical reason (e.g. configuration is needed) or to enforce a coding style, the dependency on external preprocessor state means the header isn't self contained. (And the non-self-containedness is the reason we can't include it in arbitrary contexts)

[ioeric]

clangd/index/SymbolCollector.cpp

631

That sounds good. Thanks for explaining!