Fix -Z print-type-sizes's handling of zero-sized fields.
#67215
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Currently, the type `struct S { x: u32, y: u32, tag: () }` is
incorrectly described like this:
```
print-type-size type: `S`: 8 bytes, alignment: 4 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.tag`: 0 bytes, offset: 0 bytes, alignment: 1 bytes
print-type-size padding: 4 bytes
print-type-size field `.y`: 4 bytes, alignment: 4 bytes
```
Specifically:
- The `padding` line is wrong. (There is no padding.)
- The `offset` and `alignment` on the `.tag` line shouldn't be printed.
The problem is that multiple fields can end up with the same offset, and
the printing code doesn't handle this correctly.
This commit fixes it by adjusting the field sorting so that zero-sized fields
are dealt with before non-zero-sized fields. With that in place, the
printing code works correctly.
The commit also corrects the "something is very wrong" comment.
The new output looks like this:
```
print-type-size type: `S`: 8 bytes, alignment: 4 bytes
print-type-size field `.tag`: 0 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.y`: 4 bytes
```
rust-highfive
added
the
S-waiting-on-review
|
The real-world type that I encountered this on was |
|
great catch! |
|
@bors r+ rollup |
|
📌 Commit c681841 has been approved by |
bors
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S-waiting-on-bors
JohnTitor
added a commit
to JohnTitor/rust
that referenced
this pull request
Dec 12, 2019
…ro-sized-fields, r=pnkfelix
Fix `-Z print-type-sizes`'s handling of zero-sized fields.
Currently, the type `struct S { x: u32, y: u32, tag: () }` is
incorrectly described like this:
```
print-type-size type: `S`: 8 bytes, alignment: 4 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.tag`: 0 bytes, offset: 0 bytes, alignment: 1 bytes
print-type-size padding: 4 bytes
print-type-size field `.y`: 4 bytes, alignment: 4 bytes
```
Specifically:
- The `padding` line is wrong. (There is no padding.)
- The `offset` and `alignment` on the `.tag` line shouldn't be printed.
The problem is that multiple fields can end up with the same offset, and
the printing code doesn't handle this correctly.
This commit fixes it by adjusting the field sorting so that zero-sized fields
are dealt with before non-zero-sized fields. With that in place, the
printing code works correctly.
The commit also corrects the "something is very wrong" comment.
The new output looks like this:
```
print-type-size type: `S`: 8 bytes, alignment: 4 bytes
print-type-size field `.tag`: 0 bytes
print-type-size field `.x`: 4 bytes
print-type-size field `.y`: 4 bytes
```
r? @pnkfelix
bors
added a commit
that referenced
this pull request
Dec 12, 2019
Rollup of 8 pull requests Successful merges: - #62514 (Clarify `Box<T>` representation and its use in FFI) - #66983 (Fix `unused_parens` triggers on macro by example code) - #67215 (Fix `-Z print-type-sizes`'s handling of zero-sized fields.) - #67230 (Remove irelevant comment on `register_dtor`) - #67236 (resolve: Always resolve visibilities on impl items) - #67237 (Some small readability improvements) - #67238 (Small std::borrow::Cow improvements) - #67239 (Make TinyList::remove iterate instead of recurse) Failed merges: r? @ghost
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Currently, the type
struct S { x: u32, y: u32, tag: () }isincorrectly described like this:
Specifically:
paddingline is wrong. (There is no padding.)offsetandalignmenton the.tagline shouldn't be printed.The problem is that multiple fields can end up with the same offset, and
the printing code doesn't handle this correctly.
This commit fixes it by adjusting the field sorting so that zero-sized fields
are dealt with before non-zero-sized fields. With that in place, the
printing code works correctly.
The commit also corrects the "something is very wrong" comment.
The new output looks like this:
r? @pnkfelix