https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62137
Bug ID: 62137
Summary: Poor error recovery when parsing for-loops
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: manu at gcc dot gnu.org
This has to be a common mistake:
manuel@gcc10:~$ cat parseerr.cc
void foo(void)
{
for (int k, k < 20; k++);
}
Yet we give a not very good diagnostic:
parseerr.cc:3:17: error: expected initializer before ‘<’ token
for (int k, k < 20; k++);
^
parseerr.cc:3:17: error: expected ‘;’ before ‘<’ token
parseerr.cc:3:17: error: expected primary-expression before ‘<’ token
My guess is that "k <20" is parsed as a declaration of type "int", when that
fails something goes wrong, and instead of backtracking to ",", the parser
tries to finish the declaration starting from k but finds "<" instead of ";".
The last error, well, who knows!
After seeing the first error, there are perhaps two better options:
* If we know we are in a loop header, backtrack to after consuming, assume we
have seen ";" and continue.
* If not, simply skip to next ";"
