Special case DUMMY_SP to emit line 0/column 0 locations on DWARF platforms.
Line 0 has a special meaning in DWARF. From the version 5 spec:
The compiler may emit the value 0 in cases
where an instruction cannot be attributed to any
source line.
DUMMY_SP spans cannot be attributed to any line. However, because rustc internally stores line numbers starting at zero, lookup_debug_loc() adjusts every line number by one. Special casing DUMMY_SP to actually emit line 0 ensures rustc communicates to the debugger that there's no meaningful source code for this instruction, rather than telling the debugger to jump to line 1 randomly.
Enable debuginfo tests that have been "temporarily disabled" for the past 6 years
The PR history is a bit of a mess because I had to test this a lot with try-jobs, so I'll try to summarize the non-obvious changes here.
A number of tests now have `min-lldb-version: 1800`. Those tests should have gotten an lldb version jump either in https://github.com/rust-lang/rust/pull/124781 or long ago. Note that all such tests with that lldb version requirement do not run in Apple CI.
`tests/debuginfo/drop-locations.rs` is staying disabled for now because gdb doesn't know to stop on the drop calls produced by a `}`: https://github.com/rust-lang/rust/issues/128971
`tests/debuginfo/function-arg-initialization.rs` now has `-Zmir-enable-passes=-SingleUseConsts`; without that we initialize the const before the function prelude: https://github.com/rust-lang/rust/issues/128945
`tests/debuginfo/by-value-non-immediate-argument.rs` fails because we don't generate a function prelude for unused non-immediate arguments, even with all optimizations disabled, and this seems to confuse debuggers on aarch64: https://github.com/rust-lang/rust/issues/128973
`tests/debuginfo/pretty-std.rs` is staying disabled on windows-gnu because our test harness doesn't know how to load our pretty-printers on that target: https://github.com/rust-lang/rust/issues/128981
`tests/debuginfo/method-on-enum.rs` and `tests/debuginfo/option-like-enum.rs` encounter some kind of gdb bug on i686-pc-windows-gnu. I don't know enough about that situation to write a good issue.
I plan on doing more work on this test suite. There's clearly a lot more basic cleanup work to do here.
Summary:
I landed a fix last year to enable `DW_TAG_variant_part` encoding in LLDBs (https://reviews.llvm.org/D149213). This PR is a corresponding fix in synthetic formatters to decode that information.
This is in no way perfect implementation but at least it improves the status quo. But most types of enums will be visible and debuggable in some way.
I've also updated most of the existing tests that touch enums and re-enabled test cases based on LLDB for enums.
Test Plan:
ran tests `./x test tests/debuginfo/`. Also tested manually in LLDB CLI and LLDB VSCode
Other Thoughs
A better approach would probably be adopting [formatters from codelldb](https://github.com/vadimcn/codelldb/blob/master/formatters/rust.py). There is some neat hack that hooks up summary provider via synthetic provider which can ultimately fix more display issues for Rust types and enums too. But getting it to work well might take more time that I have right now.
`-Z debug-macros` is "stabilized" by enabling it by default and removing.
`-Z collapse-macro-debuginfo` is stabilized as `-C collapse-macro-debuginfo`.
It now supports all typical boolean values (`parse_opt_bool`) in addition to just yes/no.
Default value of `collapse_debuginfo` was changed from `false` to `external` (i.e. collapsed if external, not collapsed if local).
`#[collapse_debuginfo]` attribute without a value is no longer supported to avoid guessing the default.
