[PATCH 0/2] Re: [PATCH] C/C++: add fix-it hints for various missing symbols

[David Malcolm <dmalcolm at redhat dot com>]

On Mon, 2017-08-28 at 09:22 -0600, Jeff Law wrote:
> On 07/03/2017 12:37 PM, David Malcolm wrote:
> > This patch improves our C/C++ frontends' handling of missing
> > symbols, by making c_parser_require and cp_parser_require use
> > "better" locations for the diagnostic, and insert fix-it hints,
> > under certain circumstances (see the comments in the patch for
> > full details).
> > 
> > For example, for this code with a missing semicolon:
> > 
> >   $ cat test.c
> >   int missing_semicolon (void)
> >   {
> >     return 42
> >   }
> > 
> > trunk currently emits:
> > 
> >   test.c:4:1: error: expected ‘;’ before ‘}’ token
> >    }
> >    ^
> > 
> > This patch adds a fix-it hint for the missing semicolon, and puts
> > the error at the location of the missing semicolon, printing the
> > followup token as a secondary location:
> > 
> >   test.c:3:12: error: expected ‘;’ before ‘}’ token
> >      return 42
> >               ^
> >               ;
> >    }
> >    ~
> > 
> > More examples can be seen in the test cases.
> > 
> > For reference, clang prints the following:
> > 
> >   test.c:3:12: error: expected ';' after return statement
> >     return 42
> >              ^
> >              ;
> > 
> > i.e. describing what syntactic thing came before, which
> > I think is likely to be more meaningful to the user.
> > 
> > clang can also print notes about matching opening symbols
> > e.g. the note here:
> > 
> >   missing-symbol-2.c:25:22: error: expected ']'
> >     const char test [42;
> >                        ^
> >   missing-symbol-2.c:25:19: note: to match this '['
> >     const char test [42;
> >                     ^
> > which, although somewhat redundant for this example, seems much
> > more
> > useful if there's non-trivial nesting of constructs, or more than a
> > few
> > lines separating the open/close symbols (e.g. showing a stray
> > "namespace {"
> > that the user forgot to close).
> > 
> > I'd like to implement both of these ideas as followups, but in
> > the meantime, is the fix-it hint patch OK for trunk?
> > (successfully bootstrapped & regrtested on x86_64-pc-linux-gnu)
> > 
> > gcc/c-family/ChangeLog:
> > 	* c-common.c (c_parse_error): Add RICHLOC param, and use it
> > rather
> > 	than implicitly using input_location.
> > 	(enum missing_token_insertion_kind): New enum.
> > 	(get_missing_token_insertion_kind): New function.
> > 	(maybe_suggest_missing_token_insertion): New function.
> > 	* c-common.h (c_parse_error): Add RICHLOC param.
> > 	(maybe_suggest_missing_token_insertion): New decl.
> > 
> > gcc/c/ChangeLog:
> > 	* c-parser.c (struct c_parser): Add "previous_token_loc" field.
> > 	(c_parser_consume_token): Set parser->previous_token_loc.
> > 	(c_parser_error): Rename to...
> > 	(c_parser_error_richloc): ...this, making static, and adding
> > 	"richloc" parameter, passing it to the c_parse_error call,
> > 	rather than calling c_parser_set_source_position_from_token.
> > 	(c_parser_error): Reintroduce, reimplementing in terms of the
> > 	above.
> > 	(c_parser_require): Add "type_is_unique" param.  Use
> > 	c_parser_error_richloc rather than c_parser_error, calling
> > 	maybe_suggest_missing_token_insertion.
> > 	(c_parser_parms_list_declarator): Override default value of new
> > 	"type_is_unique" param to c_parser_require.
> > 	(c_parser_asm_statement): Likewise.
> > 	* c-parser.h (c_parser_require): Add "type_is_unique" param,
> > 	defaulting to true.
> > 
> > gcc/cp/ChangeLog:
> > 	* parser.c (cp_parser_error): Add rich_location to call to
> > 	c_parse_error.
> > 	(get_required_cpp_ttype): New function.
> > 	(cp_parser_required_error): Remove calls to cp_parser_error,
> > 	instead setting a non-NULL gmsgid, and handling it if set by
> > 	calling c_parse_error, potentially with a fix-it hint.
> > 
> > gcc/testsuite/ChangeLog:
> > 	* c-c++-common/cilk-plus/AN/parser_errors.c: Update expected
> > 	output to reflect changes to reported locations of missing
> > 	symbols.
> > 	* c-c++-common/cilk-plus/AN/parser_errors2.c: Likewise.
> > 	* c-c++-common/cilk-plus/AN/parser_errors3.c: Likewise.
> > 	* c-c++-common/cilk-plus/AN/pr61191.c: Likewise.
> > 	* c-c++-common/gomp/pr63326.c: Likewise.
> > 	* c-c++-common/missing-symbol.c: New test case.
> > 	* g++.dg/cpp1y/digit-sep-neg.C: Update expected output to
> > reflect
> > 	changes to reported locations of missing symbols.
> > 	* g++.dg/cpp1y/pr65202.C: Likewise.
> > 	* g++.dg/other/do1.C: Likewise.
> > 	* g++.dg/missing-symbol-2.C: New test case.
> > 	* g++.dg/parse/error11.C: Update expected output to reflect
> > 	changes to reported locations of missing symbols.
> > 	* g++.dg/parse/pragma2.C: Likewise.
> > 	* g++.dg/template/error11.C: Likewise.
> > 	* gcc.dg/missing-symbol-2.c: New test case.
> > 	* gcc.dg/missing-symbol-3.c: New test case.
> > 	* gcc.dg/noncompile/940112-1.c: Update expected output to
> > reflect
> > 	changes to reported locations of missing symbols.
> > 	* gcc.dg/noncompile/971104-1.c: Likewise.
> > 	* obj-c++.dg/exceptions-6.mm: Likewise.
> > 	* obj-c++.dg/pr48187.mm: Likewise.
> > 	* objc.dg/exceptions-6.m: Likewise.
> 
> AFAICT, this never got moved forward after the comments from Richard
> and
> Joseph.


Here's an updated version of the patch, addressing the various issues
raised.


> > +}
> > +
> > +/* Given RICHLOC, a location for a diagnostic describing a missing
> > token
> > +   of kind TOKEN_TYPE, potentially add a fix-it hint suggesting
> > the
> > +   insertion of the token.
> > +
> > +   The location of the attemped fix-it hint depends on TOKEN_TYPE:
> 
> s/attemped/attempted/

Fixed.

> > +
> > +  if (gmsgid)
> > +    {
> > +      /* Emulate rest of cp_parser_error.  */
> > +      cp_token *token = cp_lexer_peek_token (parser->lexer);
> > +      cp_lexer_set_source_position_from_token (token);
> > +
> > +      rich_location richloc (line_table, input_location);
> 
> So is it worth trying to factor the bits you want to emulate from
> cp_parser_error so that they're shared?  Or just a comment in
> cp_parser_error in the hopes that if someone changes it in a
> meaningful
> way they'll know to come back here and potentially update this
> routine?

I ended up factoring out the shared bits into a new subroutine
(patch 1 of the kit).

> In general though it looks really good.  I think we just want to make
> a
> decision whether or not there's some way to avoid a long term
> maintenance headache noted immediately above.
> 
> jeff
> Jeff

Thanks.  Here's an updated version of the patch, split out as a 
two patch kit.

Patch 1 implements the cleanup of the duplicated code.
Patch 2 implements the fix-it hints.

Are they OK for trunk?

Dave

David Malcolm (2):
  C++: avoid partial duplicate implementation of cp_parser_error
  C/C++: add fix-it hints for various missing symbols (v2)

 gcc/c-family/c-common.c                            | 158 +++++++++++++++
 gcc/c-family/c-common.h                            |   3 +
 gcc/c/c-parser.c                                   |  29 ++-
 gcc/c/c-parser.h                                   |   3 +-
 gcc/cp/parser.c                                    | 214 ++++++++++++++-------
 .../c-c++-common/cilk-plus/AN/parser_errors.c      |   4 +-
 .../c-c++-common/cilk-plus/AN/parser_errors2.c     |   3 +-
 .../c-c++-common/cilk-plus/AN/parser_errors3.c     |   3 +-
 gcc/testsuite/c-c++-common/cilk-plus/AN/pr61191.c  |   3 +-
 gcc/testsuite/c-c++-common/gomp/pr63326.c          |  22 +--
 gcc/testsuite/c-c++-common/missing-close-symbol.c  |   2 +
 gcc/testsuite/c-c++-common/missing-symbol.c        |  35 ++--
 gcc/testsuite/g++.dg/cpp1y/digit-sep-neg.C         |   4 +-
 gcc/testsuite/g++.dg/cpp1y/pr65202.C               |   4 +-
 gcc/testsuite/g++.dg/missing-symbol-2.C            |  58 ++++++
 gcc/testsuite/g++.dg/other/do1.C                   |   4 +-
 gcc/testsuite/g++.dg/parse/error11.C               |   2 +-
 gcc/testsuite/g++.dg/parse/pragma2.C               |   4 +-
 gcc/testsuite/g++.dg/template/error11.C            |   2 +-
 gcc/testsuite/gcc.dg/missing-symbol-2.c            |  71 +++++++
 gcc/testsuite/gcc.dg/missing-symbol-3.c            |  50 +++++
 gcc/testsuite/gcc.dg/noncompile/940112-1.c         |   4 +-
 gcc/testsuite/gcc.dg/noncompile/971104-1.c         |   4 +-
 gcc/testsuite/obj-c++.dg/exceptions-6.mm           |   6 +-
 gcc/testsuite/obj-c++.dg/pr48187.mm                |   8 +-
 gcc/testsuite/objc.dg/exceptions-6.m               |   4 +-
 26 files changed, 574 insertions(+), 130 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/missing-symbol-2.C
 create mode 100644 gcc/testsuite/gcc.dg/missing-symbol-2.c
 create mode 100644 gcc/testsuite/gcc.dg/missing-symbol-3.c

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