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From: "xry111 at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/109356] Enhancement idea to provide clearer missing brace
 line number
Date: Wed, 05 Apr 2023 09:22:55 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109356

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |WONTFIX
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #4 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Jonny Grant from comment #3)
> A different example where GCC does a good job of indicating the line numb=
er
> of a missing comma problem.
>=20
>=20
> https://godbolt.org/z/asGhE3W17
>=20
>=20
> <source>:6:5: error: expected '}' before '{' token
>     6 |     {"G", "H"},
>       |     ^
> <source>:2:1: note: to match this '{'
>     2 | {
>       | ^
> <source>:6:5: error: expected ',' or ';' before '{' token
>     6 |     {"G", "H"},
>       |     ^

This is easy because the parser has to insert a comma here to correct the
syntax.  But for a missing } it can be added at one of multiple places to m=
ake
the syntax correct.

The parser always keeps progressing unless it's sure there is a syntax erro=
r.=20
Note that=20

static const char * list[][2] =3D
{
    {"A", "B"},
    {"C", "D"},
    {"E", "F",
    {"G", "H"},
    {"I", "J"}
}};

is NOT a syntax error.  It's a semantic error (violating a constraint) but =
the
parser does not know about semantics (i.e. the parser does not know what "[=
2]"
means at all).  So the parser cannot be sure about the syntax error until t=
he
last line.

Mixing the semantic analysis into the parser is not acceptable because it's=
 not
how a compiler is implemented.

Make the parser try different locations and pass all possible syntax tree to
the further passes is at least quadratic behavior and not acceptable.

I'll say this WONTFIX.  If someone knows how to do this in a rational way
please reopen.=