Re: [PATCH] RFC: C/C++: print help when a header can't be found

[Jason Merrill <jason at redhat dot com>]

On Mon, Nov 12, 2018 at 4:01 PM Martin Sebor <msebor@gmail.com> wrote:
> On 11/11/2018 04:33 PM, David Malcolm wrote:
> > When gcc can't find a header file, it's a hard error that stops the build,
> > typically requiring the user to mess around with compile flags, Makefiles,
> > dependencies, and so forth.
> >
> > Often the exact search paths aren't obvious to the user.  Consider the
> > case where the include paths are injected via a tool such as pkg-config,
> > such as e.g.:
> >
> >   gcc $(pkg-config --cflags glib-2.0) demo.c
> >
> > This patch is an attempt at being more helpful for such cases.  Given that
> > the user can't proceed until the issue is resolved, I think it's reasonable
> > to default to telling the user as much as possible about what happened.
> > This patch list all of the search paths, and any close matches (e.g. for
> > misspellings).
> >
> > Without the patch, the current behavior is:
> >
> > misspelled-header-1.c:1:10: fatal error: test-header.hpp: No such file or directory
> >     1 | #include "test-header.hpp"
> >       |          ^~~~~~~~~~~~~~~~~
> > compilation terminated.
> >
> > With the patch, the user gets this output:
> >
> > misspelled-header-1.c:1:10: fatal error: test-header.hpp: No such file or directory
> >     1 | #include "test-header.hpp"
> >       |          ^~~~~~~~~~~~~~~~~
> > misspelled-header-1.c:1:10: note: paths searched:
> > misspelled-header-1.c:1:10: note:  path: ''
> > misspelled-header-1.c:1:10: note:   not found: 'test-header.hpp'
> > misspelled-header-1.c:1:10: note:   close match: 'test-header.h'
> >     1 | #include "test-header.hpp"
> >       |          ^~~~~~~~~~~~~~~~~
> >       |          "test-header.h"
> > misspelled-header-1.c:1:10: note:  path: '/usr/include/glib-2.0' (via '-I')
> > misspelled-header-1.c:1:10: note:   not found: '/usr/include/glib-2.0/test-header.hpp'
> > misspelled-header-1.c:1:10: note:  path: '/usr/lib64/glib-2.0/include' (via '-I')
> > misspelled-header-1.c:1:10: note:   not found: '/usr/lib64/glib-2.0/include/test-header.hpp'
> > misspelled-header-1.c:1:10: note:  path: './include' (system directory)
> > misspelled-header-1.c:1:10: note:   not found: './include/test-header.hpp'
> > misspelled-header-1.c:1:10: note:  path: './include-fixed' (system directory)
> > misspelled-header-1.c:1:10: note:   not found: './include-fixed/test-header.hpp'
> > misspelled-header-1.c:1:10: note:  path: '/usr/local/include' (system directory)
> > misspelled-header-1.c:1:10: note:   not found: '/usr/local/include/test-header.hpp'
> > misspelled-header-1.c:1:10: note:  path: '/usr/include' (system directory)
> > misspelled-header-1.c:1:10: note:   not found: '/usr/include/test-header.hpp'
> > compilation terminated.
> >
> > showing the paths that were tried, and why (e.g. the -I paths injected by
> > the pkg-config invocation), and the .hpp vs .h issue (with a fix-it hint).
> >
> > It's verbose, but as I said above, the user can't proceed until they
> > resolve it, so I think being verbose is appropriate here.
> >
> > Thoughts?
>
> I think printing the directories and especially the near matches
> will be very helpful, especially for big projects with lots of -I
> options.
>
> The output could be made substantially shorter, less repetitive,
> and so easier to read -- basically cut in half -- by avoiding
> most of the duplication and collapsing two notes into one, e.g.
> like so:
>
>    fatal error: test-header.hpp: No such file or directory
>        1 | #include "test-header.hpp"
>          |          ^~~~~~~~~~~~~~~~~
>    note: paths searched:
>    note: -I '.'
>    note:   close match: 'test-header.h'
>        1 | #include "test-header.hpp"
>          |          ^~~~~~~~~~~~~~~~~
>          |          "test-header.h"
>    note: -I '/usr/include/glib-2.0'
>    note: -I '/usr/lib64/glib-2.0/include'
>    note: -isystem './include'
>    note: -isystem './include-fixed'
>    note: -isystem '/usr/local/include'
>    note: -isystem '/usr/include'
>
> or by printing the directories in sections:
>
>    note: -I paths searched:
>    note:   '.'
>    note:   close match: 'test-header.h'
>        1 | #include "test-header.hpp"
>          |          ^~~~~~~~~~~~~~~~~
>          |          "test-header.h"
>    note:   '/usr/include/glib-2.0'
>    note:   '/usr/lib64/glib-2.0/include'
>    note: -isystem paths searched:
>    note:   './include'
>    note:   './include-fixed'
>    note:   '/usr/local/include'
>    note:   '/usr/include'

I agree that the "not found" lines are unnecessary; I don't feel
strongly about the other formatting.

Jason