[RFC/PATCH] Fix-it hints

[Manuel López-Ibáñez <lopezibanez at gmail dot com>]

This patch implements fix-it hints. See https://gcc.gnu.org/PR62314

When the caret line is active (which is the default), this adds an
additional source-line indicating how to fix the code:

gcc/testsuite/g++.dg/template/crash83.C:5:21: error: an explicit
specialization must be preceded by 'template <>'
 template<typename = class A<0>: > struct B {}; // { dg-error
"explicit specialization|expected" }
                     ^
                     template<>

When the caret line is disabled with -fno-diagnostics-show-caret, the
fix-it hint is printed as:

gcc/testsuite/g++.dg/template/crash83.C:5:21: error: an explicit
specialization must be preceded by 'template <>'
gcc/testsuite/g++.dg/template/crash83.C:5:21: fixit: template<>

The latter form may allow an IDE (such as emacs) to automatically apply the fix.

Currently, fix-it hints are limited to insertions at one single
location, whereas Clang allows insertions, deletions, and replacements
at arbitrary location ranges.

Opinions? Is the proposed interface/implementation acceptable?

Any other diagnostics that could use a fix-it hint? In principle, we
should only give them when we are sure that the proposed fix will fix
the error or silence a warning.  For example, the C++ parser often
says 'x' expected before 'y' but adding x before y rarely fixes
anything.

gcc/ChangeLog:

2014-08-31  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    PR c++/62314
    * diagnostic.def (DK_FIXIT): New.
    * diagnostic.c (adjust_column): New.
    (adjust_line): Factor out adjust_column.
    (get_source_line_and_column): New.
    (diagnostic_show_locus): Call get_source_line_and_column.
    (diagnostic_action_after_output): Ignore DK_FIXIT.
    (fixit_hint): New.
    * diagnostic-core.h (fixit_hint): Declare.

gcc/cp/ChangeLog:

2014-08-31  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    PR c++/62314
    * parser.c (cp_parser_diagnose_invalid_type_name): Call fixit_hint.
    (cp_parser_expression_statement): Likewise.
    (cp_parser_class_head): Likewise. Update location.


gcc/testsuite/ChangeLog:

2014-08-31  Manuel López-Ibáñez  <manu@gcc.gnu.org>

    PR c++/62314
    * g++.old-deja/g++.oliva/typename1.C: Handle fixit hint.
    * g++.old-deja/g++.oliva/typename2.C: Likewise.
    * g++.old-deja/g++.other/typename1.C: Likewise.
    * g++.old-deja/g++.pt/typename6.C: Likewise.
    * g++.old-deja/g++.pt/typename3.C: Likewise.
    * g++.old-deja/g++.pt/typename4.C: Likewise.
    * g++.dg/parse/error36.C: Likewise.
    * g++.dg/parse/typedef2.C: Likewise.
    * g++.dg/template/error6.C: Likewise.
    * g++.dg/template/dependent-name5.C: Likewise.
    * g++.dg/template/crash83.C: Likewise.
    * g++.dg/template/typename3.C: Likewise.

Attachment: fixit-hints.diff
Description: Text document