The Audacity of Cope: catching rustc's layout panics so std can fly

.github/workflows/test-all-nightlies.yml

@@ -0,0 +1,111 @@
+name: 'Test All Nightlies'
+
+# Verifies that every breakpoint nightly (i.e., every nightly that has a
+# golden-file directory under tests/integration/expected/) builds and passes
+# integration and UI tests.  This is the safety net that catches cfg-gating
+# mistakes: a conditional match arm that compiles on the pinned nightly but
+# not on an older (or newer) one in the supported range.
+#
+# Runs on:
+#   - Weekly (Sunday 04:00 UTC): keeps the matrix green even when the branch
+#     is quiet.
+#   - Manual dispatch: for ad-hoc verification after absorbing new breakpoints.
+#   - Push to master: ensures the supported range is intact on merge.
+
+on:
+  schedule:
+    - cron: '0 4 * * 0'   # every Sunday at 04:00 UTC
+  workflow_dispatch:
+  push:
+    branches: [master, cds/the-curious-case-of-stdlib]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  # ---------------------------------------------------------------------------
+  # Discover the nightly matrix dynamically from the golden-file directories.
+  # This means adding a new breakpoint nightly (with its golden files) is
+  # sufficient to include it in CI; no workflow file edits needed.
+  # ---------------------------------------------------------------------------
+  enumerate-nightlies:
+    name: 'Enumerate nightlies'
+    runs-on: [self-hosted, linux, normal]
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: 'Build nightly matrix from golden-file directories'
+        id: set-matrix
+        run: |
+          set -euo pipefail
+          # Each directory name under tests/integration/expected/ is a nightly
+          # date string like "nightly-2025-07-15".
+          nightlies=$(
+            ls -1 tests/integration/expected/ \
+              | sort \
+              | jq -Rnc '[inputs | select(length > 0)]'
+          )
+          echo "matrix={\"nightly\":${nightlies}}" >> "$GITHUB_OUTPUT"
+          echo "Discovered nightlies: ${nightlies}"
+
+  # ---------------------------------------------------------------------------
+  # For each nightly: install the toolchain, build, run integration + UI tests.
+  # ---------------------------------------------------------------------------
+  test-nightly:
+    name: '${{ matrix.nightly }}'
+    needs: enumerate-nightlies
+    runs-on: [self-hosted, linux, normal]
+    strategy:
+      fail-fast: false
+      matrix: ${{ fromJson(needs.enumerate-nightlies.outputs.matrix) }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: 'Install nightly toolchain'
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ matrix.nightly }}
+          components: rustc-dev,llvm-tools,rust-src
+
+      - name: 'Build stable-mir-json'
+        run: |
+          RUSTUP_TOOLCHAIN=${{ matrix.nightly }} cargo build -vv
+
+      - name: 'Install jq'
+        uses: dcarbone/install-jq-action@v3
+        with:
+          version: 1.7.1
+          force: true
+
+      - name: 'Run integration tests'
+        run: |
+          RUSTUP_TOOLCHAIN=${{ matrix.nightly }} make integration-test
+
+      - name: 'Derive rustc commit for UI tests'
+        id: rustc-meta
+        run: |
+          set -euo pipefail
+          COMMIT=$(RUSTUP_TOOLCHAIN=${{ matrix.nightly }} rustc -vV | grep 'commit-hash' | cut -d' ' -f2)
+          if [ -z "$COMMIT" ]; then
+            echo "::error::Could not determine rustc commit-hash for ${{ matrix.nightly }}"
+            exit 1
+          fi
+          echo "rustc-commit=$COMMIT" >> "$GITHUB_OUTPUT"
+
+      - name: 'Check out Rust repo'
+        uses: actions/checkout@v4
+        with:
+          repository: rust-lang/rust
+          ref: ${{ steps.rustc-meta.outputs.rustc-commit }}
+          path: rust
+          fetch-depth: 1
+
+      - name: 'Run UI tests'
+        run: |
+          RUSTUP_TOOLCHAIN=${{ matrix.nightly }} RUST_DIR_ROOT=rust make test-ui

.github/workflows/test.yml

@@ -22,10 +22,31 @@ jobs:
           ref: ${{ github.event.pull_request.head.sha }}
           submodules: recursive
 
+      - name: Install yq
+        run: |
+          set -euo pipefail
+          YQ_VERSION="v4.52.4"
+          mkdir -p "$HOME/.local/bin"
+          wget -qO "$HOME/.local/bin/yq" \
+            "https://github.com/mikefarah/yq/releases/download/${YQ_VERSION}/yq_linux_amd64"
+          chmod +x "$HOME/.local/bin/yq"
+          echo "$HOME/.local/bin" >> $GITHUB_PATH
+
+      - name: 'Read nightly channel from rust-toolchain.toml'
+        id: toolchain-meta
+        run: |
+          set -euo pipefail
+          CHANNEL=$(yq -r '.toolchain.channel' rust-toolchain.toml)
+          if [ -z "$CHANNEL" ] || [ "$CHANNEL" = "null" ]; then
+            echo "::error::Could not read toolchain.channel from rust-toolchain.toml"
+            exit 1
+          fi
+          echo "channel=$CHANNEL" >> "$GITHUB_OUTPUT"
+
       - name: "Set up nightly Rust" # https://github.com/rust-lang/rustup/issues/3409
         uses: dtolnay/rust-toolchain@master
         with:
-          toolchain: nightly-2024-11-29 # Hardcoded version, same as is in the build.rs
+          toolchain: ${{ steps.toolchain-meta.outputs.channel }}
 
       - name: 'Build stable-mir-json' # rustfmt documentation claims it is unstable on code that doesn't build
         run: |
@@ -66,10 +87,31 @@ jobs:
           ref: ${{ github.event.pull_request.head.sha }}
           submodules: recursive
 
+      - name: Install yq
+        run: |
+          set -euo pipefail
+          YQ_VERSION="v4.52.4"
+          mkdir -p "$HOME/.local/bin"
+          wget -qO "$HOME/.local/bin/yq" \
+            "https://github.com/mikefarah/yq/releases/download/${YQ_VERSION}/yq_linux_amd64"
+          chmod +x "$HOME/.local/bin/yq"
+          echo "$HOME/.local/bin" >> $GITHUB_PATH
+
+      - name: 'Read nightly channel from rust-toolchain.toml'
+        id: toolchain-meta
+        run: |
+          set -euo pipefail
+          CHANNEL=$(yq -r '.toolchain.channel' rust-toolchain.toml)
+          if [ -z "$CHANNEL" ] || [ "$CHANNEL" = "null" ]; then
+            echo "::error::Could not read toolchain.channel from rust-toolchain.toml"
+            exit 1
+          fi
+          echo "channel=$CHANNEL" >> "$GITHUB_OUTPUT"
+
       - name: "Set up nightly Rust" # https://github.com/rust-lang/rustup/issues/3409
         uses: dtolnay/rust-toolchain@master
         with:
-          toolchain: nightly-2024-11-29 # Hardcoded version, same as is in the build.rs
+          toolchain: ${{ steps.toolchain-meta.outputs.channel }}
 
       - name: 'Build stable-mir-json'
         run: | # Warning check should be redundant since code-quality runs first
@@ -108,16 +150,30 @@ jobs:
             "https://github.com/mikefarah/yq/releases/download/${YQ_VERSION}/yq_linux_amd64"
           chmod +x "$HOME/.local/bin/yq"
           echo "$HOME/.local/bin" >> $GITHUB_PATH
-          yq --version
 
+      - name: 'Read nightly channel from rust-toolchain.toml'
+        id: toolchain-meta
+        run: |
+          set -euo pipefail
+          CHANNEL=$(yq -r '.toolchain.channel' rust-toolchain.toml)
+          if [ -z "$CHANNEL" ] || [ "$CHANNEL" = "null" ]; then
+            echo "::error::Could not read toolchain.channel from rust-toolchain.toml"
+            exit 1
+          fi
+          echo "channel=$CHANNEL" >> "$GITHUB_OUTPUT"
+
+      - name: "Set up nightly Rust" # https://github.com/rust-lang/rustup/issues/3409
+        uses: dtolnay/rust-toolchain@master
+        with:
+          toolchain: ${{ steps.toolchain-meta.outputs.channel }}
 
-      - name: 'Read rustc commit from rust-toolchain.toml'
+      - name: 'Derive rustc commit and check out Rust repo'
         id: rustc-meta
         run: |
           set -euo pipefail
-          COMMIT=$(yq '.metadata.rustc-commit' rust-toolchain.toml)
-          if [ -z "$COMMIT" ] || [ "$COMMIT" = "null" ]; then
-            echo "::error::metadata.rustc-commit not found in rust-toolchain.toml"
+          COMMIT=$(rustc -vV | grep 'commit-hash' | cut -d' ' -f2)
+          if [ -z "$COMMIT" ]; then
+            echo "::error::Could not determine rustc commit-hash from 'rustc -vV'"
             exit 1
           fi
           echo "rustc-commit=$COMMIT" >> "$GITHUB_OUTPUT"
@@ -130,11 +186,6 @@ jobs:
           path: rust
           fetch-depth: 1
 
-      - name: "Set up nightly Rust" # https://github.com/rust-lang/rustup/issues/3409
-        uses: dtolnay/rust-toolchain@master
-        with:
-          toolchain: nightly-2024-11-29 # Hardcoded version, same as is in the build.rs
-
       - name: 'Build stable-mir-json'
         run: | # Warning check should be redundant since code-quality runs first
           RUSTFLAGS='--deny warnings' cargo build -vv

.gitignore

@@ -1,4 +1,5 @@
 target/
 tests/ui/failing/*
 tests/ui/passing/*
-tests/ui/debug/*
+tests/ui/debug/*
+pr.md

CHANGELOG.md

@@ -12,8 +12,7 @@ retroactive best-effort summary; earlier changes were not formally tracked.
 ### Added
 - `src/compat/` module isolating all rustc internal API usage behind a stable boundary; printer/ now has zero `extern crate rustc_*` declarations and zero direct `tcx.query()` calls
 - `OpaqueInstanceKind` owned type replacing `middle::ty::InstanceKind<'tcx>`, eliminating the `'tcx` lifetime parameter from `SmirJson`, `LinkMapKey`, `FnSymInfo`, `LinkMap`, `DerivedInfo`, and `SmirJsonDebugInfo`
-- `metadata.rustc-commit` field in `rust-toolchain.toml` as single source of truth for the rustc commit used by UI tests
-- `ensure_rustc_commit.sh` helper that reads the expected commit from `rust-toolchain.toml` (via `yq`) and ensures the rust checkout (regular or bare+worktree) is at that commit; CI installs `yq` on PATH to support this
+- `ensure_rustc_commit.sh` helper that derives the rustc commit from `rustc -vV` and ensures the rust checkout (regular or bare+worktree) is at that commit
 - ADR-003 documenting compat layer design decisions and validation results from two toolchain bump stress tests (6-month and 13-month jumps)
 
 ### Changed