debuginfo: Stabilize -Z debug-macros, -Z collapse-macro-debuginfo and #[collapse_debuginfo]

[petrochenkov]

-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) - #100758 (comment) describes some debugging scenarios that motivate this default as reasonable.
#[collapse_debuginfo] attribute without a value is no longer supported to avoid guessing the default.

Stabilization report: #120845 (comment)

Closes #100758
Closes #41743
Closes #39153

[rustbot]

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[rustbot]

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

The Miri subtree was changed

cc @rust-lang/miri

[petrochenkov]

cc @davidtwco @azhogin

[davidtwco]

I haven't thoroughly reviewed the changes here but this seems sensible to me at first glance.

[petrochenkov]

I removed one fast path optimization for simplicity, so let's also run benchmarks.
@bors try @rust-timer queue

[bors]

⌛ Trying commit 78ee1bc with merge 575a7f3...

[bors]

☀️ Try build successful - checks-actions
Build commit: 575a7f3 (575a7f35a80ab18d54b08775b7bd6cc50ee4e338)

[rust-timer]

Finished benchmarking commit (575a7f3): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.6%	[-0.7%, -0.5%]	2
All ❌✅ (primary)	0.4%	[0.4%, 0.4%]	1

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.4%	[-2.4%, -2.4%]	1
Improvements ✅ (secondary)	-2.8%	[-3.2%, -2.3%]	7
All ❌✅ (primary)	-2.4%	[-2.4%, -2.4%]	1

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	40
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	40

Bootstrap: 663.718s -> 664.389s (0.10%)
Artifact size: 308.26 MiB -> 308.31 MiB (0.01%)

[petrochenkov]

Perf changes are noise.
@bors rollup=maybe

[petrochenkov]

Stabilization Report

Before this PR all spans coming from macro definitions were by default collapsed to a single span representing the macro's call site when generating debuginfo.
The option -Z debug-macros changed that behavior and preserved all spans in debuginfo without collapsing.

With this PR the -Z debug-macros option is removed and the defaults are partially swapped.
By default spans are preserved without collapsing, giving more detailed information during debugging, but only for macros coming from the current crate.
For macros from other crates the spans are still collapsed to a single call site span, this way we don't jump to code of println! and other macros from the standard library.

Attributes #[collapse_debuginfo(yes/no/external)] and command line options -C collapse-macro-debuginfo=yes/no/external (replace -Z debug-macros) provide more fine-grained control over collapsing debuginfo spans to call site, when the defaults are insufficient.

History

#41743 identified the problem with detailed debuginfo spans for macros not being available on stable channel.

rust-lang/rfcs#2117 and rust-lang/compiler-team#386 provided the solution for undesirable jumping to sources of println! and friends when detailed spans are enabled.
#99556 implemented that solution in July 2022.

#118903 added detailed tests for the feature and fixed some issues with nested macro calls in December 2023.
#119828 added some more fine grained options to the #[collapse_debuginfo] attribute, and added a command line flag -C collapse-macro-debuginfo for overriding both defaults and attributes as well in January 2024.

Design

rust-lang/compiler-team#386 gives motivation for not collapsing macros in debuginfo in general, but collapsing some macros in particular.

Comments in #100758 (comment) and below describe some possible debugging scenarios, and make a choice for the default collapsing behavior implemented in this PR.

Tests

• tests/debuginfo/collapse-debuginfo*
• tests/debuginfo/skip_second_statement*
• tests/debuginfo/lexical-scope-with-macro.rs

Documentation

src/doc/rustc/src/codegen-options/index.md in this PR and rust-lang/reference#1468 in the reference.

[petrochenkov]

@rfcbot fcp merge

[rfcbot]

Team member @petrochenkov has proposed to merge this. The next step is review by the rest of the tagged team members:

• @Aaron1011
• @cjgillot
• @compiler-errors
• @davidtwco
• @eddyb
• @estebank
• @jackh726
• @lcnr
• @matthewjasper
• @michaelwoerister
• @nagisa
• @oli-obk
• @petrochenkov
• @pnkfelix
• @wesleywiser

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

cc @rust-lang/lang-advisors: FCP proposed for lang, please feel free to register concerns.
See this document for info about what commands tagged team members can give me.

[petrochenkov]

--pass check failed me for the first time in years.
Updated the test.
@bors r=oli-obk

[bors]

📌 Commit 98804c1 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 98804c1 with merge 78aad13...

[petrochenkov]

@bors r=oli-obk

[bors]

📌 Commit 683ad6b has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 683ad6b with merge 6acb9e7...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 6acb9e7 to master...

[rust-timer]

Finished benchmarking commit (6acb9e7): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.4%	[3.4%, 3.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.0%	[1.0%, 1.0%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.0%	[1.0%, 1.0%]	1

Binary size

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.1%	[0.0%, 1.0%]	54
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	7
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 1.0%]	54

Bootstrap: 670.868s -> 670.073s (-0.12%)
Artifact size: 316.00 MiB -> 316.00 MiB (-0.00%)

[philipc]

This has broken a test in backtrace (rust-lang/backtrace-rs#617). The collapse_debuginfo attribute can be used to fix it.

The debuginfo for line 11 is now line 11 instead of the caller, as expected. However, the result of the line! (called via pos!) is still the caller. Is it intentional that line! is unaffected? It's not clear cut to me how this should work, so I want to check.

[petrochenkov]

@philipc
Test suite in this repo has the same test - tests/ui/debuginfo/backtrace-dylib-dep.rs, I updated it to preserve the previous behavior.
The test relied on specific lines being emitted into debuginfo, and since we are changing the debuginfo emitted by default behavior of such tests may also change.

[petrochenkov]

file!() and line!() are not defined in the current crate, so they are collapsed by default now, unlike pos!() and check!() defined in the current crate.

UPD: As for values returned by file!() and line!(), they follow their own logic independent from debuginfo (defined in compiler\rustc_builtin_macros\src\source_util.rs). They traverse the macro call stack until they encounter root expansion or include! and report the line/column/file at that position.

[workingjubilee]

Breaking the test was fine if it can still be configured to pass. I'm glad that we moved that test into rustc's suite, so that it can be kept current with current defaults. I'm not sure that I want to remove the copy of the test from the backtrace suite yet, but I can just copy petrochenkov's changes to fix it.