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debuginfo: slices are DW_TAG_array_type's#153238

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shua wants to merge 2 commits intorust-lang:mainfrom
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debuginfo: slices are DW_TAG_array_type's#153238
shua wants to merge 2 commits intorust-lang:mainfrom
shua:lldb-rcstr

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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
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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rustbot commented May 5, 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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A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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