Run token-based CI in a secure way.

This protects our token secrets from PR attackers. Exposing github secure tokens
as part of random PR build system is a security risk:
https://securitylab.github.com/research/github-actions-preventing-pwn-requests/

Instead, we should export the relevant PR information and then run the workflow
which has our tokens.

Should fix #226.

.github/workflows/ci.yml

@@ -259,7 +259,6 @@ jobs:
             compiler: gcc-6
             clang-runtime: '11'
             coverage: true
-            clang-format: true
 
           - name: ubu18-gcc8-runtime11
             os: ubuntu-18.04
@@ -300,6 +299,17 @@ jobs:
     - uses: actions/checkout@v2
       with:
         fetch-depth: 0
+    - name: Save PR Info
+      if: ${{ matrix.coverage == true }}
+      run: |
+        mkdir -p ./pr
+        echo ${{ github.event.number }} > ./pr/NR
+        echo ${{ github.repository }} > ./pr/REPO
+    - uses: actions/upload-artifact@v2
+      if: ${{ matrix.coverage == true }}
+      with:
+        name: pr
+        path: pr/
     - uses: nelonoel/[email protected]
     - name: Setup default Build Type
       run: |
@@ -566,15 +576,6 @@ jobs:
         python3 -m pip show lit
         cat obj/CMakeCache.txt
         cat obj/CMakeFiles/*.log
-    - name: Invoke workflow clang-format on compiler-research
-      if: ${{ success() && (matrix.clang-format == true) }}
-      uses: benc-uk/workflow-dispatch@v1
-      with:
-        workflow: SuggestFormattingChanges
-        repo: compiler-research/knowall
-        token: ${{ secrets.PERSONAL_TOKEN }}
-        ref: main # The SuggestFormattingChanges branch
-        inputs: '{ "repo": "${{ github.repository }}", "pull_id": "${{ github.event.number }}" }'
     - name: Setup tmate session
       if: ${{ failure() }}
       uses: mxschmitt/action-tmate@v3

.github/workflows/postci.yml

@@ -0,0 +1,56 @@
+name: PostMain
+on:
+  workflow_run:
+    workflows: [Main]
+    types: [completed]
+
+jobs:
+  knowall:
+    runs-on: ubuntu-latest
+    if: >
+      ${{ github.event.workflow_run.event == 'pull_request'}}
+    steps:
+    - name: 'Download artifact'
+      uses: actions/[email protected]
+      with:
+        script: |
+          var artifacts = await github.actions.listWorkflowRunArtifacts({
+            owner: context.repo.owner,
+            repo: context.repo.repo,
+            run_id: ${{github.event.workflow_run.id }},
+          });
+          var matchArtifact = artifacts.data.artifacts.filter((artifact) => {
+            return artifact.name == "pr"
+          })[0];
+          var download = await github.actions.downloadArtifact({
+            owner: context.repo.owner,
+            repo: context.repo.repo,
+            artifact_id: matchArtifact.id,
+            archive_format: 'zip',
+          });
+          var fs = require('fs');
+          fs.writeFileSync('${{github.workspace}}/pr.zip', Buffer.from(download.data));
+    - run: |
+        unzip pr.zip
+        cat ./NR
+        cat ./REPO
+        echo "PR_NUMBER=`cat ./NR`" >> $GITHUB_ENV
+        echo "PR_REPO=`cat ./REPO`" >> $GITHUB_ENV
+
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+
+    - name: Invoke workflow clang-format on compiler-research
+      uses: benc-uk/workflow-dispatch@v1
+      with:
+        workflow: SuggestFormattingChanges
+        repo: compiler-research/knowall
+        token: ${{ secrets.PERSONAL_TOKEN }}
+        ref: main # The SuggestFormattingChanges branch
+        inputs: '{ "repo": "$PR_REPO", "pull_id": "$PR_NUMBER" }'
+
+    - name: Failed job config
+      if: ${{ failure() }}
+      run: |
+        export