Speed up CodeQL workflow

.github/workflows/codeql-analysis.yml

@@ -4,11 +4,6 @@
 # You may wish to alter this file to override the set of languages analyzed,
 # or to provide custom queries or build logic.
 #
-# ******** NOTE ********
-# We have attempted to detect the languages in your repository. Please check
-# the `language` matrix defined below to confirm you have the correct set of
-# supported CodeQL languages.
-#
 name: "CodeQL"
 
 on:
@@ -20,35 +15,56 @@ on:
   schedule:
     - cron: '34 0 * * 5'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 jobs:
   analyze:
-    name: Analyze
+    name: Analyze (${{ matrix.language }}, ${{ matrix.shard }})
     runs-on:
       group: Large
       labels: [ubuntu-latest-x64-16core]
 
     strategy:
       fail-fast: false
+      # C# is split by sample folder so dependency restore and extraction run in parallel.
+      # Each shard uploads results under its own category.
       matrix:
-        language: [ 'csharp', 'javascript' ]
-        # CodeQL supports [ 'cpp', 'csharp', 'go', 'java', 'javascript', 'python' ]
-        # Learn more:
-        # https://docs.github.com/en/free-pro-team@latest/github/finding-security-vulnerabilities-and-errors-in-your-code/configuring-code-scanning#changing-the-languages-that-are-analyzed
+        include:
+          - language: csharp
+            shard: IdentityServer/v7
+          - language: csharp
+            shard: IdentityServer/v8
+          - language: csharp
+            shard: BFF
+          - language: csharp
+            shard: various
+          - language: javascript
+            shard: all
 
     steps:
+    # C# buildless extraction scans the whole checkout regardless of source-root, so C# shards
+    # sparse-checkout only their folder (cone mode keeps root files such as global.json and nuget.config).
     - name: Checkout repository
       uses: actions/checkout@v4
+      with:
+        sparse-checkout: ${{ matrix.shard != 'all' && matrix.shard || '' }}
 
     # Analysis runs without compiling the samples; compilation is verified by the Build workflow.
     - name: Initialize CodeQL
       uses: github/codeql-action/init@9e8d0789d4a0fa9ceb6b1738f7e269594bdd67f0
       with:
         languages: ${{ matrix.language }}
         build-mode: none
+        source-root: ${{ matrix.shard == 'all' && '.' || matrix.shard }}
         # If you wish to specify custom queries, you can do so here or in a config file.
         # By default, queries listed here will override any specified in a config file.
         # Prefix the list here with "+" to use these queries and those in the config file.
         # queries: ./path/to/local/query, your-org/your-repo/queries@main
 
     - name: Perform CodeQL Analysis
       uses: github/codeql-action/analyze@9e8d0789d4a0fa9ceb6b1738f7e269594bdd67f0
+      with:
+        # JavaScript keeps its pre-sharding default category so existing alerts continue to update.
+        category: ${{ matrix.language == 'javascript' && '.github/workflows/codeql-analysis.yml:analyze/language:javascript/' || format('/language:{0}/{1}', matrix.language, matrix.shard) }}