It helps if the repo is checked out before referencing scripts in it

Author: dmachaj

.github/workflows/CheckClangFormatting.ps1

@@ -11,9 +11,37 @@ jobs:
     name: 'Check Formatting of Changes'
     runs-on: windows-latest
     steps:
+      - uses: actions/checkout@v4
+
       - name: Check Formatting
         run: |
-          cmd /c "powershell .\.github\Workflows\CheckClangFormatting.ps1"
+          $VSDevCmd = & "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere" -latest -find Common7\tools\VSDevCmd.bat
+          if (!$VSDevCmd) { exit 1 }
+          Write-Host "Using VSDevCmd: ${VSDevCmd}"
+          & $VSDevCmd;
+
+          & .\find_clang_format.cmd
+          if ($LASTEXITCODE -ne 0) {
+            exit $LASTEXITCODE
+          }
+
+          & git clang-format origin/master --binary "$env:CLANG_FORMAT" --style file -- cppwinrt/*.h cppwinrt/*.cpp fast_fwd/*.h fast_fwd/*.cpp prebuild/*.h prebuild/*.cpp scratch/*.h scratch/*.cpp strings/*.h strings/*.cpp test/*.h test/*.cpp vsix/*.h vsix/*.cpp
+
+          if ($LASTEXITCODE -ne 0) {
+            Write-Host ::error ERROR: This branch contains changes that have not been formatted with `'clang-format`'
+            Write-Host NOTE:  To resolve this issue, you can run `'clang-format`' in the following ways:
+            Write-Host        * Run ``build_test_all.cmd`` which will run `'clang-format`' on _all_ source files. This script is
+            Write-Host          simpler to run, however there`'s a chance it may touch additional files you never changed due to you having
+            Write-Host          a mis-matched version of `'clang-format`'. This may require you to manually revert changes made by
+            Write-Host          `'clang-format`' to the locations where you made no code changes.
+            Write-Host
+            Write-Host        For more information, please see https://github.com/microsoft/cppwinrt?tab=readme-ov-file#formatting
+            Write-Host
+            Write-Host NOTE:  As an additional note, given that different versions of `'clang-format`' may have different behaviors, this
+            Write-Host        may be a false positive. If you believe that to be the case ^`(e.g. none of the above resulted in modifications
+            Write-Host        to the code you have changed^`), please note this in your PR.
+            exit 1
+          }
 
   test-msvc-cppwinrt-build:
     name: '${{ matrix.compiler }}: Build (${{ matrix.arch }}, ${{ matrix.config }})'