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debuginfo: slices are DW_TAG_array_type's#153238

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debuginfo: slices are DW_TAG_array_type's#153238
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@shua shua commented Mar 1, 2026 •
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Rust debuginfo for unsized structs with embedded slice types is lacking, and it makes it difficult for debuggers to correctly print types like Rc<str> (eg #114195). Specifically, these three structs would have essentially the same debug info (modulo some names):

struct Foo { a: u32, s: str } // unsized
struct Bar { a: u32, s: [u8] } // unsized
struct Baz { a: u32, s: u8 }

This changes how the compiler generates debuginfo in this case, and I used existing compilers (gcc, clang) handling of C flexible member arrays as a reference.

@rustbot rustbot added A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Mar 1, 2026
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rustbot commented Mar 1, 2026

r? @davidtwco

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shua commented Mar 1, 2026 •
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another relevant thread from gdb bugtracker about rust's weird unsized type debug info and some related fixes in gdb: https://sourceware.org/bugzilla/show_bug.cgi?id=30330 . The type of change here (changing slice types to be array types with no count, similar to C's VLA/FMA) was discussed but I guess never implemented in rustc?

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davidtwco reviewed Mar 10, 2026
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Could you also add a codegen-llvm test for the debuginfo?

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@Enselic Enselic added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 25, 2026
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shua commented May 6, 2026

@rustbot ready

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels May 6, 2026
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davidtwco commented May 15, 2026

@bors r+

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rust-bors Bot commented May 15, 2026

📌 Commit f398585 has been approved by davidtwco

It is now in the queue for this repository.

@rust-bors rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 15, 2026
Zalathar added a commit to Zalathar/rust that referenced this pull request May 15, 2026
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Rollup merge of rust-lang#153238 - shua:lldb-rcstr, r=davidtwco
013b57b 
debuginfo: slices are DW_TAG_array_type's

Rust debuginfo for unsized structs with embedded slice types is lacking, and it makes it difficult for debuggers to correctly print types like `Rc<str>` (eg rust-lang#114195). Specifically, these three structs would have essentially the same debug info (modulo some names):
```rust
struct Foo { a: u32, s: str } // unsized
struct Bar { a: u32, s: [u8] } // unsized
struct Baz { a: u32, s: u8 }
```

This changes how the compiler generates debuginfo in this case, and I used existing compilers (gcc, clang) handling of C flexible member arrays as a reference.
@Zalathar Zalathar mentioned this pull request May 15, 2026
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rust-bors Bot pushed a commit that referenced this pull request May 15, 2026
@bors
Auto merge of #156610 - Zalathar:rollup-uLJGkLm, r=Zalathar
07d4408 
Rollup of 11 pull requests

Successful merges:

 - #148788 (Unconstrained parameter fix)
 - #153238 (debuginfo: slices are DW_TAG_array_type's)
 - #155521 (Add lint againts invalid runtime symbol definitions)
 - #156319 (Require EIIs to be defined when we compile a rust dylib)
 - #156452 (Implement pinned drop sugar)
 - #156600 (Make const param default test reproduce original ICE)
 - #156493 (actually run the temp_dir doctest)
 - #156556 (Require UTF-8 in `Utf8Pattern::StringPattern`)
 - #156565 (delegation: emit error when self type is not specified and accessed)
 - #156586 (Use DropCtxt::new_block and new_block_with_statements systematically.)
 - #156587 (Correctly handle associated items in rustdoc macro expansion)
JonathanBrouwer added a commit to JonathanBrouwer/rust that referenced this pull request May 15, 2026
@JonathanBrouwer
Rollup merge of rust-lang#153238 - shua:lldb-rcstr, r=davidtwco
ae95a55 
debuginfo: slices are DW_TAG_array_type's

Rust debuginfo for unsized structs with embedded slice types is lacking, and it makes it difficult for debuggers to correctly print types like `Rc<str>` (eg rust-lang#114195). Specifically, these three structs would have essentially the same debug info (modulo some names):
```rust
struct Foo { a: u32, s: str } // unsized
struct Bar { a: u32, s: [u8] } // unsized
struct Baz { a: u32, s: u8 }
```

This changes how the compiler generates debuginfo in this case, and I used existing compilers (gcc, clang) handling of C flexible member arrays as a reference.
@JonathanBrouwer JonathanBrouwer mentioned this pull request May 15, 2026
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rust-bors Bot pushed a commit that referenced this pull request May 15, 2026
@bors
Auto merge of #156613 - JonathanBrouwer:rollup-cKseJsM, r=JonathanBro…
af919b9 
…uwer

Rollup of 12 pull requests

Successful merges:

 - #153238 (debuginfo: slices are DW_TAG_array_type's)
 - #156319 (Require EIIs to be defined when we compile a rust dylib)
 - #156452 (Implement pinned drop sugar)
 - #156554 (Allow user-provided `llvm_args` to override target spec arguments)
 - #156571 (Disable `main_needs_argc_argv` for Wasm)
 - #156600 (Make const param default test reproduce original ICE)
 - #156493 (actually run the temp_dir doctest)
 - #156556 (Require UTF-8 in `Utf8Pattern::StringPattern`)
 - #156565 (delegation: emit error when self type is not specified and accessed)
 - #156586 (Use DropCtxt::new_block and new_block_with_statements systematically.)
 - #156587 (Correctly handle associated items in rustdoc macro expansion)
 - #156604 (coverage: Reduce and clarify the context-mismatch test case)
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JonathanBrouwer commented May 15, 2026

@bors r-
#156613 (comment)

@rust-bors rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels May 15, 2026
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rust-bors Bot commented May 15, 2026

This pull request was unapproved.

This PR was contained in a rollup (#156613), which was unapproved.

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rustbot commented May 16, 2026

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

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shua commented May 16, 2026

Is there a way to run the tests that failed in the rollup PR (auto - aarch64-msvc-1, try - x86_64-mingw-1, try - x86_64-msvc-1) on this PR? I think I fixed the issue, but I'm not able to check msvc compile targets on my machine.

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JonathanBrouwer commented May 16, 2026

@bors try jobs=aarch64-msvc-1,x86_64-mingw-1,x86_64-msvc-1

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rust-bors Bot pushed a commit that referenced this pull request May 16, 2026
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Auto merge of #153238 - shua:lldb-rcstr, r=<try>
df9eabd 
debuginfo: slices are DW_TAG_array_type's


try-job: aarch64-msvc-1
try-job: x86_64-mingw-1
try-job: x86_64-msvc-1
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shua commented May 16, 2026

@bors try jobs=aarch64-msvc-1,x86_64-mingw-1,x86_64-msvc-1

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rust-bors Bot commented May 16, 2026

@shua: 🔑 Insufficient privileges: not in try users

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JonathanBrouwer commented May 16, 2026

@bors try jobs=aarch64-msvc-1,x86_64-mingw-1,x86_64-msvc-1

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rust-bors Bot commented May 16, 2026 •
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⌛ Trying commit d2b5baf with merge 2468142…

(The previously running try build was automatically cancelled.)

To cancel the try build, run the command @bors try cancel.

Workflow: https://github.com/rust-lang/rust/actions/runs/25959675021

rust-bors Bot pushed a commit that referenced this pull request May 16, 2026
@bors
Auto merge of #153238 - shua:lldb-rcstr, r=<try>
2468142 
debuginfo: slices are DW_TAG_array_type's


try-job: aarch64-msvc-1
try-job: x86_64-mingw-1
try-job: x86_64-msvc-1
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