coverage: Remove all unstable support for MC/DC instrumentation - #144999

Zalathar · 2025-08-06T13:15:13Z

Preliminary support for a partial implementation of “Modified Condition/Decision Coverage” instrumentation was added behind the unstable flag -Zcoverage-options=mcdc in 2024. These are the most substantial PRs involved:

At the time, I accepted these PRs with relatively modest scrutiny, because I did not want to stand in the way of independent work on MC/DC instrumentation. My hope was that ongoing work by interested contributors would lead to the code becoming clearer and more maintainable over time.

However, that MC/DC code has proven itself to be a major burden on overall maintenance of coverage instrumentation, and a major obstacle to other planned improvements, such as internal changes needed for proper support of macro expansion regions.

I have also become reluctant to accept any further MC/DC-related changes that would increase this burden.

That tension has resulted in an unhappy impasse. On one hand, the present MC/DC implementation is not yet complete, and shows little sign of being complete at an acceptable level of code quality in the foreseeable future. On the other hand, the continued existence of this partial MC/DC implementation is imposing serious maintenance burdens on every other aspect of coverage instrumentation, and is preventing some of the very improvements that would make it easier to accept expanded MC/DC support in the future.

While I know this will be disappointing to some, I think the healthy way forward is accept that I made the wrong call in accepting the current implementation, and to remove it entirely from the compiler.

rustbot · 2025-08-06T13:15:18Z

r? @matthewjasper

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rustbot · 2025-08-06T13:15:21Z

Some changes occurred in match lowering

cc @Nadrieril

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

oli-obk · 2025-08-07T10:52:30Z

r? @oli-obk

@bors r+

bors · 2025-08-07T10:52:33Z

📌 Commit 81ed042 has been approved by oli-obk

It is now in the queue for this repository.

Rollup of 19 pull requests Successful merges: - #144400 (`tests/ui/issues/`: The Issues Strike Back [3/N]) - #144764 ([codegen] assume the tag, not the relative discriminant) - #144807 (Streamline config in bootstrap) - #144899 (Print CGU reuse statistics in `-Zprint-mono-items`) - #144909 (Add new `test::print_merged_doctests_times` used by rustdoc to display more detailed time information) - #144912 (Resolver: introduce a conditionally mutable Resolver for (non-)speculative resolution.) - #144914 (Add support for `ty::Instance` path shortening in diagnostics) - #144931 ([win][arm64ec] Fix msvc-wholearchive for Arm64EC) - #144999 (coverage: Remove all unstable support for MC/DC instrumentation) - #145009 (A couple small changes for rust-analyzer next-solver work) - #145030 (GVN: Do not flatten derefs with ProjectionElem::Index. ) - #145042 (stdarch subtree update) - #145047 (move `type_check` out of `compute_regions`) - #145051 (Prevent name collisions with internal implementation details) - #145053 (Add a lot of NLL `known-bug` tests) - #145055 (Move metadata symbol export from exported_non_generic_symbols to exported_symbols) - #145057 (Clean up some resolved test regressions of const trait removals in std) - #145068 (Readd myself to review queue) - #145070 (Add minimal `armv7a-vex-v5` tier three target) r? `@ghost` `@rustbot` modify labels: rollup

Rollup merge of #144999 - Zalathar:remove-mcdc, r=oli-obk coverage: Remove all unstable support for MC/DC instrumentation Preliminary support for a partial implementation of “Modified Condition/Decision Coverage” instrumentation was added behind the unstable flag `-Zcoverage-options=mcdc` in 2024. These are the most substantial PRs involved: - #123409 - #126733 At the time, I accepted these PRs with relatively modest scrutiny, because I did not want to stand in the way of independent work on MC/DC instrumentation. My hope was that ongoing work by interested contributors would lead to the code becoming clearer and more maintainable over time. --- However, that MC/DC code has proven itself to be a major burden on overall maintenance of coverage instrumentation, and a major obstacle to other planned improvements, such as internal changes needed for proper support of macro expansion regions. I have also become reluctant to accept any further MC/DC-related changes that would increase this burden. That tension has resulted in an unhappy impasse. On one hand, the present MC/DC implementation is not yet complete, and shows little sign of being complete at an acceptable level of code quality in the foreseeable future. On the other hand, the continued existence of this partial MC/DC implementation is imposing serious maintenance burdens on every other aspect of coverage instrumentation, and is preventing some of the very improvements that would make it easier to accept expanded MC/DC support in the future. While I know this will be disappointing to some, I think the healthy way forward is accept that I made the wrong call in accepting the current implementation, and to remove it entirely from the compiler.

Rollup of 19 pull requests Successful merges: - rust-lang/rust#144400 (`tests/ui/issues/`: The Issues Strike Back [3/N]) - rust-lang/rust#144764 ([codegen] assume the tag, not the relative discriminant) - rust-lang/rust#144807 (Streamline config in bootstrap) - rust-lang/rust#144899 (Print CGU reuse statistics in `-Zprint-mono-items`) - rust-lang/rust#144909 (Add new `test::print_merged_doctests_times` used by rustdoc to display more detailed time information) - rust-lang/rust#144912 (Resolver: introduce a conditionally mutable Resolver for (non-)speculative resolution.) - rust-lang/rust#144914 (Add support for `ty::Instance` path shortening in diagnostics) - rust-lang/rust#144931 ([win][arm64ec] Fix msvc-wholearchive for Arm64EC) - rust-lang/rust#144999 (coverage: Remove all unstable support for MC/DC instrumentation) - rust-lang/rust#145009 (A couple small changes for rust-analyzer next-solver work) - rust-lang/rust#145030 (GVN: Do not flatten derefs with ProjectionElem::Index. ) - rust-lang/rust#145042 (stdarch subtree update) - rust-lang/rust#145047 (move `type_check` out of `compute_regions`) - rust-lang/rust#145051 (Prevent name collisions with internal implementation details) - rust-lang/rust#145053 (Add a lot of NLL `known-bug` tests) - rust-lang/rust#145055 (Move metadata symbol export from exported_non_generic_symbols to exported_symbols) - rust-lang/rust#145057 (Clean up some resolved test regressions of const trait removals in std) - rust-lang/rust#145068 (Readd myself to review queue) - rust-lang/rust#145070 (Add minimal `armv7a-vex-v5` tier three target) r? `@ghost` `@rustbot` modify labels: rollup

rust-lang/rust#144999

Rollup of 19 pull requests Successful merges: - rust-lang#144400 (`tests/ui/issues/`: The Issues Strike Back [3/N]) - rust-lang#144764 ([codegen] assume the tag, not the relative discriminant) - rust-lang#144807 (Streamline config in bootstrap) - rust-lang#144899 (Print CGU reuse statistics in `-Zprint-mono-items`) - rust-lang#144909 (Add new `test::print_merged_doctests_times` used by rustdoc to display more detailed time information) - rust-lang#144912 (Resolver: introduce a conditionally mutable Resolver for (non-)speculative resolution.) - rust-lang#144914 (Add support for `ty::Instance` path shortening in diagnostics) - rust-lang#144931 ([win][arm64ec] Fix msvc-wholearchive for Arm64EC) - rust-lang#144999 (coverage: Remove all unstable support for MC/DC instrumentation) - rust-lang#145009 (A couple small changes for rust-analyzer next-solver work) - rust-lang#145030 (GVN: Do not flatten derefs with ProjectionElem::Index. ) - rust-lang#145042 (stdarch subtree update) - rust-lang#145047 (move `type_check` out of `compute_regions`) - rust-lang#145051 (Prevent name collisions with internal implementation details) - rust-lang#145053 (Add a lot of NLL `known-bug` tests) - rust-lang#145055 (Move metadata symbol export from exported_non_generic_symbols to exported_symbols) - rust-lang#145057 (Clean up some resolved test regressions of const trait removals in std) - rust-lang#145068 (Readd myself to review queue) - rust-lang#145070 (Add minimal `armv7a-vex-v5` tier three target) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 19 pull requests Successful merges: - rust-lang/rust#144400 (`tests/ui/issues/`: The Issues Strike Back [3/N]) - rust-lang/rust#144764 ([codegen] assume the tag, not the relative discriminant) - rust-lang/rust#144807 (Streamline config in bootstrap) - rust-lang/rust#144899 (Print CGU reuse statistics in `-Zprint-mono-items`) - rust-lang/rust#144909 (Add new `test::print_merged_doctests_times` used by rustdoc to display more detailed time information) - rust-lang/rust#144912 (Resolver: introduce a conditionally mutable Resolver for (non-)speculative resolution.) - rust-lang/rust#144914 (Add support for `ty::Instance` path shortening in diagnostics) - rust-lang/rust#144931 ([win][arm64ec] Fix msvc-wholearchive for Arm64EC) - rust-lang/rust#144999 (coverage: Remove all unstable support for MC/DC instrumentation) - rust-lang/rust#145009 (A couple small changes for rust-analyzer next-solver work) - rust-lang/rust#145030 (GVN: Do not flatten derefs with ProjectionElem::Index. ) - rust-lang/rust#145042 (stdarch subtree update) - rust-lang/rust#145047 (move `type_check` out of `compute_regions`) - rust-lang/rust#145051 (Prevent name collisions with internal implementation details) - rust-lang/rust#145053 (Add a lot of NLL `known-bug` tests) - rust-lang/rust#145055 (Move metadata symbol export from exported_non_generic_symbols to exported_symbols) - rust-lang/rust#145057 (Clean up some resolved test regressions of const trait removals in std) - rust-lang/rust#145068 (Readd myself to review queue) - rust-lang/rust#145070 (Add minimal `armv7a-vex-v5` tier three target) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 19 pull requests Successful merges: - rust-lang#144400 (`tests/ui/issues/`: The Issues Strike Back [3/N]) - rust-lang#144764 ([codegen] assume the tag, not the relative discriminant) - rust-lang#144807 (Streamline config in bootstrap) - rust-lang#144899 (Print CGU reuse statistics in `-Zprint-mono-items`) - rust-lang#144909 (Add new `test::print_merged_doctests_times` used by rustdoc to display more detailed time information) - rust-lang#144912 (Resolver: introduce a conditionally mutable Resolver for (non-)speculative resolution.) - rust-lang#144914 (Add support for `ty::Instance` path shortening in diagnostics) - rust-lang#144931 ([win][arm64ec] Fix msvc-wholearchive for Arm64EC) - rust-lang#144999 (coverage: Remove all unstable support for MC/DC instrumentation) - rust-lang#145009 (A couple small changes for rust-analyzer next-solver work) - rust-lang#145030 (GVN: Do not flatten derefs with ProjectionElem::Index. ) - rust-lang#145042 (stdarch subtree update) - rust-lang#145047 (move `type_check` out of `compute_regions`) - rust-lang#145051 (Prevent name collisions with internal implementation details) - rust-lang#145053 (Add a lot of NLL `known-bug` tests) - rust-lang#145055 (Move metadata symbol export from exported_non_generic_symbols to exported_symbols) - rust-lang#145057 (Clean up some resolved test regressions of const trait removals in std) - rust-lang#145068 (Readd myself to review queue) - rust-lang#145070 (Add minimal `armv7a-vex-v5` tier three target) r? `@ghost` `@rustbot` modify labels: rollup

Rollup of 19 pull requests Successful merges: - rust-lang/rust#144400 (`tests/ui/issues/`: The Issues Strike Back [3/N]) - rust-lang/rust#144764 ([codegen] assume the tag, not the relative discriminant) - rust-lang/rust#144807 (Streamline config in bootstrap) - rust-lang/rust#144899 (Print CGU reuse statistics in `-Zprint-mono-items`) - rust-lang/rust#144909 (Add new `test::print_merged_doctests_times` used by rustdoc to display more detailed time information) - rust-lang/rust#144912 (Resolver: introduce a conditionally mutable Resolver for (non-)speculative resolution.) - rust-lang/rust#144914 (Add support for `ty::Instance` path shortening in diagnostics) - rust-lang/rust#144931 ([win][arm64ec] Fix msvc-wholearchive for Arm64EC) - rust-lang/rust#144999 (coverage: Remove all unstable support for MC/DC instrumentation) - rust-lang/rust#145009 (A couple small changes for rust-analyzer next-solver work) - rust-lang/rust#145030 (GVN: Do not flatten derefs with ProjectionElem::Index. ) - rust-lang/rust#145042 (stdarch subtree update) - rust-lang/rust#145047 (move `type_check` out of `compute_regions`) - rust-lang/rust#145051 (Prevent name collisions with internal implementation details) - rust-lang/rust#145053 (Add a lot of NLL `known-bug` tests) - rust-lang/rust#145055 (Move metadata symbol export from exported_non_generic_symbols to exported_symbols) - rust-lang/rust#145057 (Clean up some resolved test regressions of const trait removals in std) - rust-lang/rust#145068 (Readd myself to review queue) - rust-lang/rust#145070 (Add minimal `armv7a-vex-v5` tier three target) r? `@ghost` `@rustbot` modify labels: rollup

Rust stable -C instrument-coverage only emits block/region data (0 BRDA records in lcov). Branch coverage requires -Z coverage-options= branch (nightly-gated). RUSTC_BOOTSTRAP=1 unlocks -Z flags on the stable toolchain — coverage-only, non-instrumented builds stay pure stable for CI parity. Applied to both: - rio-workspace-cov (VM tests): RUSTFLAGS + RUSTC_BOOTSTRAP in covArgs - unit-test coverage: cargo-llvm-cov --branch + RUSTC_BOOTSTRAP genhtml --branch-coverage in both coverage-html and coverage-full so the HTML shows branch hit/miss annotations. Verified: minimal if/else test emits 2 BRDA records, 1 hit. Note: rust-lang/rust#144999 removed MC/DC (mcdc option), NOT branch. Valid options on rustc 1.93+nightly: block | branch | condition.

Rollup of 19 pull requests Successful merges: - rust-lang/rust#144400 (`tests/ui/issues/`: The Issues Strike Back [3/N]) - rust-lang/rust#144764 ([codegen] assume the tag, not the relative discriminant) - rust-lang/rust#144807 (Streamline config in bootstrap) - rust-lang/rust#144899 (Print CGU reuse statistics in `-Zprint-mono-items`) - rust-lang/rust#144909 (Add new `test::print_merged_doctests_times` used by rustdoc to display more detailed time information) - rust-lang/rust#144912 (Resolver: introduce a conditionally mutable Resolver for (non-)speculative resolution.) - rust-lang/rust#144914 (Add support for `ty::Instance` path shortening in diagnostics) - rust-lang/rust#144931 ([win][arm64ec] Fix msvc-wholearchive for Arm64EC) - rust-lang/rust#144999 (coverage: Remove all unstable support for MC/DC instrumentation) - rust-lang/rust#145009 (A couple small changes for rust-analyzer next-solver work) - rust-lang/rust#145030 (GVN: Do not flatten derefs with ProjectionElem::Index. ) - rust-lang/rust#145042 (stdarch subtree update) - rust-lang/rust#145047 (move `type_check` out of `compute_regions`) - rust-lang/rust#145051 (Prevent name collisions with internal implementation details) - rust-lang/rust#145053 (Add a lot of NLL `known-bug` tests) - rust-lang/rust#145055 (Move metadata symbol export from exported_non_generic_symbols to exported_symbols) - rust-lang/rust#145057 (Clean up some resolved test regressions of const trait removals in std) - rust-lang/rust#145068 (Readd myself to review queue) - rust-lang/rust#145070 (Add minimal `armv7a-vex-v5` tier three target) r? `@ghost` `@rustbot` modify labels: rollup

… (RQ-57-MCDC) (#978) * feat(#912): MC/DC structural coverage over synth's own decision logic RQ-57-MCDC. #912 sat N/A for six releases on a surface argument: `witness` measures MC/DC on a Wasm artifact and synth emits ARM/RV32/A64 machine code, so "run witness on synth's output" is a category error. That is true about synth's OUTPUT and irrelevant — the decisions that ship a miscompile are in synth's own Rust, and those compile to Wasm fine. SURFACE, chosen on evidence (scripts/repro/mcdc_912_gate.md): * REJECTED native LLVM MC/DC — not a preference, the capability was REMOVED from rustc (rust-lang/rust#144999, merged 2025-08-08, Rust 1.91). Probed on three nightlies: `mcdc` is rejected, only `block|branch|condition` accepted. `condition` is the trap in the family — it builds, and it emits ZERO `llvm.instrprof.mcdc.*` intrinsics and zero mcdc_records. * REJECTED witness-over-the-fixtures-synth-compiles — it measures the fixture. gale's run named `pad_integral`, `do_count_chars`, `<u64 as Display>::fmt`, `write_prefix`, `cabi_realloc` and ZERO synth functions. A surface whose gap rows cannot name a synth decision cannot notice a missing condition in one. * CHOSEN witness over a wasm32-wasip1 build of synth's OWN crates. `synth-mcdc-harness` is a thin row driver — it calls the REAL pub fns with inputs arriving through Wasm params; it re-implements no predicate. THE RIGHT PARTS — scored where a missed condition HAS shipped a bug here: static_data_addr (VCR-VER-003 #777/#757/#798), alloc_validator (VCR-RA-003 #815; #871's fix WAS a condition added to the save-set predicate), and the RV32 bounds gate (#953/#959 — `mem_size == 0` was exempt from the power-of-two check, so `(memory 0)` emitted an identity mask and every access ran unmasked). EXCLUDED and named: instruction_selector (225 operator lines, its own lane); the aarch64 bounds closures (#865 — residual); wcet declines (match-dispatch, 1 operator line in 1061, so MC/DC has nothing to say there). MEASURED 20 decisions / 144 conditions / 63 proved / 31 gap / 50 dead, 3 at full MC/DC. Identical under witness 0.28.0 and 0.42.0. Gap rows are PRINTED with the closing vector — `is_ret` went 3-gap to 0-gap by adding exactly the three vectors witness named. THE GATE SCORES BY FUNCTION AND FLOORS COUNTS, for three reasons: the module-wide figure is 3/770 because wasip1 links wasi-libc + std; witness's `source_file` is an inlined-DWARF BASENAME and misattributes (resolve_owner's decision reports as static_data_addr.rs:355, it is at :274 — witness#179); and a ratio cannot notice a DELETED condition, which makes the percentage improve. RED-FIRST, two mutations, two distinct failure paths, both restored byte-identical: (a) delete `|| rs2 == Reg::RA` (the #871 fix) -> 19/142/54/2, all four floors trip; the condition-COUNT drop is what a ratio cannot produce. (b) drop one truth-table row (ra_validate:14) -> conditions stay 144, proved 63->62 and fully-proved 3->2. Wired as the `mcdc-structural-coverage` CI job, witness pinned to v0.42.0, with a non-vacuity assert so an empty scored table cannot print PASS. Refs #912 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01YJK5LZZEkV5smCY1jKn18L * fix(#912): CI mode-126 on mcdc_run.sh, pin the toolchain, ceiling the dead count Three fixes from the first CI run and the cold read of it: 1. exit 126. `scripts/` is mode 644 in this repo (cf. scripts/oracle_run.py), so `./scripts/mcdc_run.sh` cannot exec on a fresh checkout even though it runs locally after a chmod. Invoke through `bash`, matching how every other script in this workflow is called. 2. PIN the toolchain to 1.96.1. The floors are counts of decisions and conditions RECONSTRUCTED FROM LOWERED WASM, so they are sensitive to how `std` inlines. `@stable` is a moving target and a Rust release could red this gate with no code change. Bumping the pin is allowed and obliges a RE-MEASURE, not a lowering. (Witness-version invariance — 0.28 = 0.42 — is evidence about witness, not about rustc; it does not transfer.) 3. CEILING the dead count at the measured 50. 50 of 144 scored conditions are never evaluated (40 in `is_straight_line`, whose match arms cover RV32 opcodes the row set does not construct). That residual was the one number in the table nothing guarded: a change that stopped reaching the segment barriers would raise `dead`, lower nothing else, and PASS. It is also a third potency surface — mutation (a) moves dead 50 -> 52, so the mutated run now trips five floors instead of four. Also trims the `sd_resolve_owner` doc comment, which claimed vectors the measurement does not show: its 2 gap conditions are now stated as a measured residual rather than implied closed. Baseline re-verified unchanged: 20 / 3 / 144 / 63 / 31 / 50, PASS. Refs #912 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01YJK5LZZEkV5smCY1jKn18L * TEMPORARY red-first probe (#912) — DO NOT MERGE THIS COMMIT Reverted by the very next commit. Two things in one CI run: 1. RE-MEASURE the floors on the platform the gate actually runs on. The first CI run proved what could only be argued locally: these counts are PLATFORM-dependent, not just toolchain-version dependent. ubuntu x86_64, rustc 1.96.1, witness 0.42.0: 22 / 130 / 57 / 23 gap / 50 dead, 4 full macOS aarch64, rustc 1.96.1, witness 0.42.0: 20 / 144 / 63 / 31 gap / 50 dead, 3 full Same toolchain version, same witness, same 56 rows, different host. `validate_final_allocation_rv32` presents as 9 decisions / 44 conditions on Linux and 4 / 43 on macOS; `ensure_supported_target` vanishes on Linux. Floors move to the CI numbers — RE-MEASURED, not lowered to fit. Both baselines are recorded in the script so the macOS delta is a stated fact rather than a surprise. 2. RE-PROVE POTENCY ON THAT PLATFORM. The local mutation evidence does NOT obviously transfer when the same function presents as 9 decisions instead of 4 — and "it obviously still works" is the reasoning this whole lane exists to distrust. So this commit ALSO deletes the #871 condition `|| rs2 == Reg::RA` from the RV32 allocation validator's save-set predicate. The MC/DC job must go RED on the condition-COUNT floor, and the VCR-RA-003 RV32 job should go red independently. If this commit is green, the gate is vacuous and the lane is wrong. Refs #912 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01YJK5LZZEkV5smCY1jKn18L * TEMPORARY red-first probe 2/2 (#912) — DO NOT MERGE, reverted next commit Probe 1 (25a9195) went RED on CI as required, but at the WRONG STEP for the evidence I wanted: the row-driver sanity gate (step 7) asserts `ra_validate(4) == 1` (#871: unsaved ra must be a violation), so deleting `|| rs2 == Reg::RA` fails there and the MC/DC measurement never runs. Two independent gates catching one mutation is good engineering and useless as proof that the MC/DC FLOORS bite. This probe isolates them. It restores the source byte-identical (verified: empty `git diff` vs the pre-mutation tree) and instead drops ONE truth-table row — `ra_validate:14`, the non-sp `Lw` that gives `sp_slot_load` its unique-cause pair. That touches no compiler behaviour, so: step 7 (row-driver sanity) must PASS step 8 (witness run) must PASS step 9 (MC/DC floors) must FAIL on and Conditions must stay at 130 — coverage lost, nothing deleted. That is the second of the two potency paths, and the one that proves the SCORING floor itself is what goes red, on the platform it actually runs on. Refs #912 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01YJK5LZZEkV5smCY1jKn18L * chore(#912): restore the probes, record the CI-platform potency evidence Both red-first probes reverted; the tree is byte-identical to 712f658 for crates/synth-backend-riscv/src/alloc_validator.rs and scripts/mcdc_run.sh (verified with an empty \$(git diff 712f658 -- <path>) on each). What the two CI probes established, which the local run could not: PROBE 1 (delete the #871 condition) went RED — at the WRONG STEP. The job's own row-driver sanity gate asserts ra_validate(4) == 1 and fails there, so the MC/DC measurement never ran; the VCR-RA-003 RV32 job went red independently too. Three gates catching one mutation is good engineering and NO evidence that the MC/DC floors bite. Recording it because 'a red gate is not evidence that the gate you were testing works' generalises well past this lane — read WHICH STEP failed. PROBE 2 (drop one truth-table row, no compiler behaviour touched) isolated them. Run 31821746035: sanity gate PASS, witness run PASS, SCORING STEP FAIL. baseline 22 4 130 57 23 50 probe 2 22 3 130 56 24 50 FAIL: proved conditions 56 < floor 57 FAIL: fully-proved decisions 3 < floor 4 Decisions unchanged, CONDITIONS UNCHANGED at 130 — nothing deleted — while proved fell and a decision dropped out of full MC/DC. That is the signature of coverage lost with structure intact, produced by the MC/DC scoring step itself, on the platform the gate blocks on. Refs #912 Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01YJK5LZZEkV5smCY1jKn18L --------- Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

coverage: Remove all unstable support for MC/DC instrumentation

81ed042

Zalathar added A-code-coverage Area: Source-based code coverage (-Cinstrument-coverage) F-coverage-mcdc MC/DC coverage via -Cinstrument-coverage with -Zcoverage-options=mcdc labels Aug 6, 2025

rustbot assigned matthewjasper Aug 6, 2025

rustbot assigned oli-obk and unassigned matthewjasper Aug 7, 2025

bors 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 Aug 7, 2025

Zalathar mentioned this pull request Aug 8, 2025

Rollup of 19 pull requests #145077

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bors merged commit 562222b into rust-lang:master Aug 8, 2025
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rustbot added this to the 1.91.0 milestone Aug 8, 2025

Zalathar deleted the remove-mcdc branch August 8, 2025 09:36

taiki-e added a commit to taiki-e/cargo-llvm-cov that referenced this pull request Aug 10, 2025

ci: Unstable MC/DC support has been removed in upstream

48538fb

rust-lang/rust#144999

Nadrieril mentioned this pull request Oct 8, 2025

Support mcdc analysis for pattern matching #124278

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This was referenced May 1, 2026

docs(README): retire TQL aspiration; spell out independence + MC/DC limits luofang34/Evidence#114

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feat(boundary): DAL-A MC/DC fail-loud at cert/record; warn at dev luofang34/Evidence#115

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avrabe mentioned this pull request Aug 14, 2026

chore(release): v0.57.0 — "the checkers were the defects" pulseengine/synth#980

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coverage: Remove all unstable support for MC/DC instrumentation - #144999