https://issues.dlang.org/show_bug.cgi?id=24617
Issue ID: 24617
Summary: array runtime erroneously copies flags from existing
block
Product: D
Version: D2
Hardware: All
OS: All
Status: NEW
Severity: minor
Priority: P1
Component: druntime
Assignee: nob...@puremagic.com
Reporter: schvei...@gmail.com
If an array slice starts from a GC allocated block that is *not* marked
appendable, the appendable flag never gets set until appending occurs.
example:
```d
struct S
{
int[1] val;
}
void main()
{
auto s = new S;
int[] arr = s.val[];
assert(arr.capacity == 0); // starts out without appendability
arr.length = 2;
assert(arr.capacity > 0); // this fails
arr.reserve(100);
assert(arr.capacity > 0); // this fails
arr ~= 10;
assert(arr.capacity > 0); // finally, this succeeds
}
```
The issue is that the `__arrayAlloc` function copies the original bits instead
of using the typeinfo to decide the new array bits if a BlkInfo has already
been looked up. I guess the thought is that using the TypeInfo to build the
bits is more expensive, and we "already have something".
Options are to just always use the typeinfo, or to check for the appendable bit
before using the old bits (but copying the other bits might be questionable as
well).
--
