On Tue, 2020-10-06 at 21:37 +0300, Eli Zaretskii wrote: > > From: David Malcolm > > Cc: 25987@debbugs.gnu.org > > Date: Tue, 06 Oct 2020 14:17:55 -0400 > > > > In GCC 11 we've revamped the column number handling in how we emit > > diagnostics; see: > > > > https://gcc.gnu.org/pipermail/gcc-patches/2020-October/555632.html > > > > GCC 11 diagnostics now (by default) should use actual column > > numbers, > > rather than byte counts. > > That's good news, thanks. > > > We haven't changed -fdiagnostics-parseable-fixits; it still emits > > its > > range information in terms of byte offsets (and e.g. Eclipse > > already > > consumes that option); this is bug-for-bug compatible with clang, I > > believe (which had that option first). > > So fixit hints will still count bytes? Or will GCC 11 emit such > hints even without -fdiagnostics-parseable-fixits on the command > line? > > > Note that characters != columns, or, at least, we have to be > > careful > > about what we mean. Consider the case of 🙂 aka SLIGHTLY SMILING > > FACE > > (U+1F642) which is a single unicode code point, but occupies two > > columns, with its UTF-8 encoding requiring four bytes. > > > > When I type it into an Emacs buffer, and look at the column number > > I > > see that Emacs appears to treat the character as occupying two > > columns. > > Is that the kind of column numbering you would want for machine- > > readable fix-it hints? > > Yes. Emacs computes the width of each character by using UCD, the > Unicode Character Database (specifically, the EastAsianWidth.txt file > that is part of the UCD). If GCC gets its column counts from a > similar DB, then it will match what Emacs does. > > > Similarly, the column numbering emitted by GCC 11 diagnostics is > > affected by tab characters as tab stops, which seems to reflect > > Emacs > > behavior as well. > > Yes. > > > I can add an additional option for fix-it hints that's similar to > > -fdiagnostics-parseable-fixits, but with a different output format > > (or > > to add an argument to that option, perhaps). > > If an option is needed for getting the hints, then a special option > which reports columns in hints will be appreciated, as it will make > the Emacs support for processing those hints 100% accurate and devoid > of encoding guesswork. > > > Before I do that, I wanted to check that it would be consumable by > > Emacs. What works for you? Would it help to send the proposed GCC > > patch to this bug address (or to the emacs-devel list?). > > I don't know how many people here build their own GCC, and thus could > try the patch, but if sending the patch is not too much trouble, > perhaps posting it on emacs-devel would be a good idea. If you do > that, please cite this bug report, so that people who try that could > respond here with their experience. > > > Alternatively, we already have a JSON output option (-fdiagnostics- > > format=json); perhaps something like that could be used? > > Emacs can parse JSON. What are the pros and cons of the JSON > alternative wrt to the text alternative? The existing "-fdiagnostics-format=json" GCC option replaces the existing diagnostic output with a big blob of JSON to stderr, all on one line. Although I implemented it, I now feel it to be rather half- baked. I like how -fdiagnostics-parseable-fixits adds extra lines of output, with a prefix that's ought to be easy to detect. BTW, does Emacs set anything in the environment that GCC could detect? > > Feature freeze for GCC 11 is about a month away; I'd love for Emacs > > to > > be able to consume GCC fix-it hints (and have GCC and Emacs fix my > > typos for me) > > Agreed; let's try to make that happen. I put together a test file showing various features to try to ensure that GCC and Emacs interoperate on this. I'm attaching it. This can also be seen on Compiler Explorer at: https://godbolt.org/z/zazejq which adds the existing -fdiagnostics-parseable-fixits -fdiagnostics-generate-patch options. Ideas for other test cases are most welcome. Does Emacs have an automated test suite that could test this feature? A long-postponed goal for me for GCC's testsuite is to ensure that fix- it hints apply and actually fix the problem (clang's testsuite has tests that verify this for clang's fix-it hints). Another complication to consider: the locations in a fix-it hint refer to the original source file, before any changes are made. If the user interface supports the user e.g. clicking on fix-it hints and selectively apply them one by one, then after each fix-it hint is applied, all locations after that point potentially need to be "fixed up" somehow, to reflect the changes to the buffer. GCC's own code implements this in gcc/edit-context.{c|h}, for implementing - fdiagnostics-generate-patch, which applies all fix-its "atomically" - but the use-case I thinking of involves clicking on fix-it hints one- by-one in the compilation buffer, perhaps replacing the fix-it output with an "Apply fix" button. (to cover this case I made sure the demo file contained examples of a fix-it hint that adds a line, and one that has multiple fix-it hints on the same line). Thoughts? Dave