Add warning annotation in CI.

Author: marcalff

.github/workflows/iwyu.yml

@@ -62,10 +62,16 @@ jobs:
 
       - name: count warnings
         run: |
+          set +e
           cd build
-          export WARNING_COUNT=`grep -c "include-what-you-use reported diagnostics:" iwyu.log`
+          readonly WARNING_COUNT=`grep -c "include-what-you-use reported diagnostics:" iwyu.log`
           echo "include-what-you-use reported ${WARNING_COUNT} warning(s)"
           # Acceptable limit, to decrease over time down to 0
-          export WARNING_LIMIT=10
+          readonly WARNING_LIMIT=10
           # FAIL the build if WARNING_COUNT > WARNING_LIMIT
-          exit $(( WARNING_COUNT > WARNING_LIMIT ? 1 : 0 ))
+          if [ $WARNING_COUNT -gt $WARNING_LIMIT ] ; then
+            exit 1
+          # WARN in annotations if WARNING_COUNT > 0
+          elif [ $WARNING_COUNT -gt 0 ] ; then
+            echo "::warning::include-what-you-use reported ${WARNING_COUNT} warning(s)"
+          fi