PR checks: Compare the default and latest CodeQL tools bundles

Create a prerequisite job that runs the init step twice, with `tools: null` and `tools: latest`.
Use the outputs of these steps to compare the two CodeQL versions.
Pass the list of distinct tool versions for the integration tests to use in their matrix strategy.
This avoids redundant test jobs when the default and latest bundles are actually the same version of CodeQL.

`~` is accepted by JSON but not by the Actions context language, so we use `null` to indicate the default version.

.github/workflows/pr-checks.yml

@@ -80,13 +80,65 @@ jobs:
           exit 1
         fi
 
-  multi-language-repo_test-custom-queries-and-remote-config:
+  # Identify the CodeQL tool versions to integration test against.
+  check-codeql-versions:
     needs: [check-js, check-node-modules]
+    runs-on: ubuntu-latest
+    outputs:
+      versions: ${{ steps.compare.outputs.versions }}
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Move codeql-action
+      shell: bash
+      run: |
+        mkdir ../action
+        mv * .github ../action/
+        mv ../action/tests/multi-language-repo/{*,.github} .
+        mv ../action/.github/workflows .github
+    - name: Init with default CodeQL bundle from the VM image
+      id: init-default
+      uses: ./../action/init
+      with:
+        languages: javascript
+    - name: Remove empty database
+      # allows us to run init a second time
+      run: |
+        rm -rf "$RUNNER_TEMP/codeql_databases"
+    - name: Init with latest CodeQL bundle
+      id: init-latest
+      uses: ./../action/init
+      with:
+        tools: latest
+        languages: javascript
+    - name: Compare default and latest CodeQL bundle versions
+      id: compare
+      env:
+        CODEQL_DEFAULT: ${{ steps.init-default.outputs.codeql-path }}
+        CODEQL_LATEST: ${{ steps.init-latest.outputs.codeql-path }}
+      run: |
+        CODEQL_VERSION_DEFAULT="$("$CODEQL_DEFAULT" version --format terse)"
+        CODEQL_VERSION_LATEST="$("$CODEQL_LATEST" version --format terse)"
+        echo "Default CodeQL bundle version is $CODEQL_VERSION_DEFAULT"
+        echo "Latest CodeQL bundle version is $CODEQL_VERSION_LATEST"
+        if [[ "$CODEQL_VERSION_DEFAULT" == "$CODEQL_VERSION_LATEST" ]]; then
+          # Just use `tools: null` to avoid duplication in the integration tests.
+          VERSIONS_JSON='[null]'
+        else
+          # Use both `tools: null` and `tools: latest` in the integration tests.
+          VERSIONS_JSON='[null, "latest"]'
+        fi
+        # Output a JSON-encoded list with the distinct versions to test against.
+        echo "Suggested matrix config for integration tests: $VERSIONS_JSON"
+        echo "::set-output name=versions::${VERSIONS_JSON}"
+
+  multi-language-repo_test-custom-queries-and-remote-config:
+    needs: [check-js, check-node-modules, check-codeql-versions]
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        tools: [~, latest]
+        tools: ${{ fromJson(needs.check-codeql-versions.outputs.versions) }}
     runs-on: ${{ matrix.os }}
 
     steps:
@@ -112,12 +164,12 @@ jobs:
 
   # Currently is not possible to analyze Go in conjunction with other languages in macos
   multi-language-repo_test-go-custom-queries:
-    needs: [check-js, check-node-modules]
+    needs: [check-js, check-node-modules, check-codeql-versions]
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        tools: [~, latest]
+        tools: ${{ fromJson(needs.check-codeql-versions.outputs.versions) }}
     runs-on: ${{ matrix.os }}
 
     steps:
@@ -146,12 +198,12 @@ jobs:
         TEST_MODE: true
 
   go-custom-tracing:
-    needs: [check-js, check-node-modules]
+    needs: [check-js, check-node-modules, check-codeql-versions]
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        tools: [~, latest]
+        tools: ${{ fromJson(needs.check-codeql-versions.outputs.versions) }}
     runs-on: ${{ matrix.os }}
     env:
       CODEQL_EXTRACTOR_GO_BUILD_TRACING: "on"
@@ -181,11 +233,11 @@ jobs:
         TEST_MODE: true
 
   go-custom-tracing-autobuild:
-    needs: [check-js, check-node-modules]
+    needs: [check-js, check-node-modules, check-codeql-versions]
     strategy:
       fail-fast: false
       matrix:
-        tools: [~, latest]
+        tools: ${{ fromJson(needs.check-codeql-versions.outputs.versions) }}
     # No need to test Go autobuild on multiple OSes since
     # we're testing Go custom tracing with a manual build on all OSes.
     runs-on: ubuntu-latest
@@ -244,11 +296,11 @@ jobs:
         TEST_MODE: true
 
   test-proxy:
-    needs: [check-js, check-node-modules]
+    needs: [check-js, check-node-modules, check-codeql-versions]
     strategy:
       fail-fast: false
       matrix:
-        tools: [~, latest]
+        tools: ${{ fromJson(needs.check-codeql-versions.outputs.versions) }}
     runs-on: ubuntu-latest
     container:
       image: ubuntu:18.04