https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91506
Bug ID: 91506
Summary: Incorrectly issued error: parameter may not have
variably modified type
Product: gcc
Version: 9.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: abbeyj+gcc at gmail dot com
Target Milestone: ---
Compiling:
double test(int *arr, int x) {
double ret(double(arr[x]) + 1);
return ret;
}
produces:
<source>: In function 'double test(int*, int)':
<source>:2:23: error: parameter may not have variably modified type 'double
[x]'
2 | double ret(double(arr[x]) + 1);
| ^~~
It looks like this could be a Most Vexing Parse situation but clang, ICC and
MSVC accept it. GCC accepts this similar code which doesn't seem like it
should be treated differently from the above:
double test(int *arr, int x) {
int y = x;
double ret(double(arr[y]) + 1);
return ret;
}
Compiling with -std=c++03 changes things so GCC accepts the testcase.
Compiling with -Wvla gets you an additional warning:
<source>:2:23: warning: variable length array 'arr' is used [-Wvla]
2 | double ret(double(arr[x]) + 1);
| ^~~
This makes it seem like GCC is parsing this as a function declaration. But
after the error is issued GCC ends up treating `ret` as having type `double`,
not as a function; changing the code to something like `return ret.foo();`
produces an error saying `... 'ret', which is of non-class type 'double'`.
Testing on godbolt.org shows that this is reproducible all the way back to
4.6.4 (if using `-std=c++0x`). Version 4.5.3 does not exhibit the problem.
Possibly related to bug 41786 ?
