Rework Toolchain model and drop relative file path overrides

Relative path overrides permit a freshly downloaded source tree to
execute arbitrary code on any rustup command that executes a binary from
the configured toolchain, and its a reasonable tradeoff for us to remove
this feature. Absolute path overrides are kept intact - these were added
to support users of large monorepo tool systems, and can be kept with
reasonable safety.

Introduce an interior model for toolchain names which allows the
elimination of conditional code for custom vs named vs path based
toolchains. Fixes #3130.

Finishes the separation of Toolchain vs DistributableToolchain vs
CustomToolchain started some time ago.

Moves some test support into the src tree in order to keep symbols
private and adds a 'test' feature required for self-testing, ensuring
that that code doesn't affect production builds.

Changes the CI debug builds to use the new test feature and also otel,
so that otel doesn't bitrot.

.github/workflows/all-features.yaml

@@ -0,0 +1,46 @@
+name: AllFeatures (PR)
+
+# This is an additional workflow to test building with all feature combinations.
+# Unlike our main workflows, this doesn't self-test the rustup install scripts,
+# nor run on the rust docker images. This permits a smaller workflow without the
+# templating and so on.
+
+on:
+  pull_request:
+    branches:
+      - "*"
+      - renovate/*
+
+jobs:
+  build:
+    name: Build
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        # Might add more targets in future.
+        target:
+          - x86_64-unknown-linux-gnu
+    steps:
+      - name: Clone repo
+        uses: actions/checkout@v3
+      - name: Install rustup stable
+        run: rustup toolchain install stable --profile minimal
+      - name: Install Protoc
+        uses: arduino/setup-protoc@v1
+        with:
+          version: "3.x"
+      - name: Set environment variables appropriately for the build
+        run: |
+          echo "$HOME/.cargo/bin" >> $GITHUB_PATH
+          echo "TARGET=${{ matrix.target }}" >> $GITHUB_ENV
+      - name: Cache Cargo
+        uses: Swatinem/rust-cache@v2
+      - name: Install cargo-all-features
+        run: cargo install cargo-all-features --git https://github.com/rbtcollins/cargo-all-features.git
+      - name: Ensure we have our goal target installed
+        run: |
+          rustup target install "$TARGET"
+      - name: Build every combination
+        run: |
+          cargo check-all-features --root-only

.github/workflows/centos-fmt-clippy-on-all.yaml

@@ -22,7 +22,8 @@ jobs:
     strategy:
       fail-fast: false
     steps:
-      - uses: actions/checkout@v3
+      - name: Clone repo
+        uses: actions/checkout@v3
         with:
           # v2 defaults to a shallow checkout, but we need at least to the previous tag
           fetch-depth: 0
@@ -71,6 +72,10 @@ jobs:
         run: |
           rustup component add rustfmt
           rustup component add clippy
+      - name: Install Protoc
+        uses: arduino/setup-protoc@v1
+        with:
+          version: '3.x'
       - name: Run the centos check within the docker image
         run: |
           docker run \
@@ -91,6 +96,6 @@ jobs:
           cargo fmt --all --check
       - name: Run cargo check and clippy
         run: |
-          cargo check --all --all-targets
+          cargo check --all --all-targets --features test
           git ls-files -- '*.rs' | xargs touch
-          cargo clippy --all --all-targets
+          cargo clippy --all --all-targets --features test

.github/workflows/linux-builds-on-master.yaml

@@ -98,6 +98,10 @@ jobs:
           echo "DOCKER=$DOCKER" >> $GITHUB_ENV
       - name: Fetch the docker
         run: bash ci/fetch-rust-docker.bash "${TARGET}"
+      - name: Install Protoc
+        uses: arduino/setup-protoc@v1
+        with:
+          version: '3.x'
       - name: Maybe build a docker from there
         run: |
           if [ -f "ci/docker/$DOCKER/Dockerfile" ]; then

.github/workflows/linux-builds-on-pr.yaml

@@ -92,6 +92,10 @@ jobs:
           echo "DOCKER=$DOCKER" >> $GITHUB_ENV
       - name: Fetch the docker
         run: bash ci/fetch-rust-docker.bash "${TARGET}"
+      - name: Install Protoc
+        uses: arduino/setup-protoc@v1
+        with:
+          version: '3.x'
       - name: Maybe build a docker from there
         run: |
           if [ -f "ci/docker/$DOCKER/Dockerfile" ]; then

.github/workflows/linux-builds-on-stable.yaml

@@ -121,6 +121,10 @@ jobs:
           echo "DOCKER=$DOCKER" >> $GITHUB_ENV
       - name: Fetch the docker
         run: bash ci/fetch-rust-docker.bash "${TARGET}"
+      - name: Install Protoc
+        uses: arduino/setup-protoc@v1
+        with:
+          version: '3.x'
       - name: Maybe build a docker from there
         run: |
           if [ -f "ci/docker/$DOCKER/Dockerfile" ]; then

.github/workflows/windows-builds-on-master.yaml

@@ -113,9 +113,9 @@ jobs:
           TARGET: ${{ matrix.target }} 
         # os-specific code leads to lints escaping if we only run this in one target
         run: |
-          cargo check --all --all-targets
+          cargo check --all --all-targets --features test
           git ls-files -- '*.rs' | xargs touch
-          cargo clippy --workspace --all-targets      
+          cargo clippy --workspace --all-targets --features test   
       - name: Upload the built artifact
         if: matrix.mode == 'release'
         uses: actions/upload-artifact@v3

.github/workflows/windows-builds-on-pr.yaml

@@ -107,9 +107,9 @@ jobs:
           TARGET: ${{ matrix.target }} 
         # os-specific code leads to lints escaping if we only run this in one target
         run: |
-          cargo check --all --all-targets
+          cargo check --all --all-targets --features test
           git ls-files -- '*.rs' | xargs touch
-          cargo clippy --workspace --all-targets      
+          cargo clippy --workspace --all-targets --features test   
       - name: Upload the built artifact
         if: matrix.mode == 'release'
         uses: actions/upload-artifact@v3

.github/workflows/windows-builds-on-stable.yaml

@@ -116,9 +116,9 @@ jobs:
           TARGET: ${{ matrix.target }} 
         # os-specific code leads to lints escaping if we only run this in one target
         run: |
-          cargo check --all --all-targets
+          cargo check --all --all-targets --features test
           git ls-files -- '*.rs' | xargs touch
-          cargo clippy --workspace --all-targets      
+          cargo clippy --workspace --all-targets --features test   
       - name: Upload the built artifact
         if: matrix.mode == 'release'
         uses: actions/upload-artifact@v3

CONTRIBUTING.md

@@ -2,7 +2,7 @@
 
 1. Fork it!
 2. Create your feature branch: `git checkout -b my-new-feature`
-3. Test it: `cargo test`
+3. Test it: `cargo test --features=test`
 4. Lint it: `cargo +beta clippy --all --all-targets -- -D warnings`
 > We use `cargo clippy` to ensure high-quality code and to enforce a set of best practices for Rust programming. However, not all lints provided by `cargo clippy` are relevant or applicable to our project.
 > We may choose to ignore some lints if they are unstable, experimental, or specific to our project.
@@ -312,7 +312,7 @@ And [look in Jaeger for a trace](http://localhost:16686/search?service=rustup).
 
 The custom macro `rustup_macros::test` adds a prelude and suffix to each test to
 ensure that there is a tracing context setup, that the test function is a span,
-and that the spans from the test are flushed. Build with features=otel to
+and that the spans from the test are flushed. Build with features=otel,test to
 use this feature.
 
 ### Adding instrumentation