On Sat, 2020-11-14 at 14:43 -0500, David Malcolm wrote: > GCC has had the ability to emit fix-it hints in machine-readable form > since GCC 7 via -fdiagnostics-parseable-fixits and > -fdiagnostics-generate-patch. > > The former emits additional specially-formatted lines to stderr; the > option and its format were directly taken from a pre-existing option > in clang. > > Ideally this could be used by IDEs so that the user can select > specific > fix-it hints and have the IDE apply them to the user's source code > (perhaps turning them into clickable elements, perhaps with an > "Apply All" option, etc). Eclipse CDT has supported this option in > this way for a few years: > https://bugs.eclipse.org/bugs/show_bug.cgi?id=497670 > > As a user of Emacs I would like Emacs to support such a feature. > https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25987 tracks supporting > GCC fix-it output in Emacs. The discussion there identifies some > issues with the existing option: > > (a) columns in the output are specified as byte-offsets within the > line (for exact compatibility with the option in clang), whereas > emacs > would prefer to consume them as what GCC 11 calls "display columns". > https://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Message-Formatting-Options.html#index-fdiagnostics-column-unit > > (b) injecting a command-line option into the build is a fiddly manual > step, varying between build systems. It's far easier for the > user if Emacs simply sets an environment variable when compiling, > GCC uses this to enable the option if it recognizes the value, and > the emacs compilation buffer decodes the additional lines of output > and adds appropriate widgets. In some ways it is a workaround for > not having a language server. Doing it this way means that for the > various combinations of older and newer GCC and older and newer Emacs > that a sufficiently modern combination of both can automatically > support the rich fix-it UI, whereas other combinations will either > not provide the envvar, or silently ignore it, gracefully doing > nothing extra. > > Hence this patch adds a new GCC_EXTRA_DIAGNOSTIC_OUTPUT environment > variable to GCC which enables output of machine-parseable fix-it > hints. > > GCC_EXTRA_DIAGNOSTIC_OUTPUT=fixits-v1 is equivalent to the existing > -fdiagnostics-parseable-fixits option. > > GCC_EXTRA_DIAGNOSTIC_OUTPUT=fixits-v2 is the same, but changes the > column output mode to "display columns" rather than bytes, as > required by Emacs. > > One remaining issue raised in that Emacs bug is the encoding of these > lines, and, indeed, the encoding of GCC's stderr in general: > currently we emit a mixture of bytes and UTF-8; I believe we emit > filenames as bytes, diagnostic messages as UTF-8, and quote source > code > in the original encoding (PR other/93067 covers converting it to UTF- > 8 on > output). Currently this patch prints octal-escaped bytes for bytes > within filenames and replacement text that aren't printable (which > is what -fdiagnostics-parseable-fixits also does). Doing so at least > allows the common case of ASCII-encoded sources and filenames to > work, > whilst allowing for future formats that address the encoding issues. > > Successfully bootstrapped & regrtested on x86_64-pc-linux-gnu. > > Thoughts? > Dave
In the absence of feedback, I've rebased the patch, retested it as above, and pushed it to master (as f10960558540636800cf5d3d6355969621fbc17e) Dave
