PowerShell · daxian-dbw · Dec 2, 2025 · Oct 31, 2025 · Copilot · Dec 2, 2025
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+# Merge Conflict Checker
+
+This composite GitHub Action checks for Git merge conflict markers in files changed in pull requests.
+
+## Purpose
+
+Automatically detects leftover merge conflict markers (`<<<<<<<`, `=======`, `>>>>>>>`) in pull request files to prevent them from being merged into the codebase.
+
+## Usage
+
+### In a Workflow
+
+```yaml
+- name: Check for merge conflict markers
+  uses: "./.github/actions/infrastructure/merge-conflict-checker"
+```
+
+### Complete Example
+
+```yaml
+jobs:
+  merge_conflict_check:
+    name: Check for Merge Conflict Markers
+    runs-on: ubuntu-latest
+    if: github.event_name == 'pull_request'
+    permissions:
+      pull-requests: read
+      contents: read
+    steps:
+      - name: checkout
+        uses: actions/checkout@v5
+
+      - name: Check for merge conflict markers
+        uses: "./.github/actions/infrastructure/merge-conflict-checker"
+```
+
+## How It Works
+
+1. **File Detection**: Uses GitHub's API to get the list of files changed in the pull request
+2. **Marker Scanning**: Reads each changed file and searches for the following markers:
+   - `<<<<<<<` (conflict start marker)
+   - `=======` (conflict separator)
+   - `>>>>>>>` (conflict end marker)
+3. **Result Reporting**: 
+   - If markers are found, the action fails and lists all affected files
+   - If no markers are found, the action succeeds
+
+## Outputs
+
+- `files-checked`: Number of files that were checked
+- `conflicts-found`: Number of files containing merge conflict markers
+
+## Behavior
+
+- **Event Support**: Only works with `pull_request` events
+- **File Handling**:
+  - Checks only files that were added, modified, or renamed
+  - Skips deleted files
+  - **Filters out `*.cs` files** (C# files are excluded from merge conflict checking)
-  - **Filters out `*.cs` files** (C# files are excluded from merge conflict checking)
+  - **Filters out `*.cs` files** (C# files are excluded from merge conflict checking to avoid false positives from C# build-generated files, which may contain patterns resembling merge conflict markers)
-  - **Filters out `*.cs` files** (C# files are excluded from merge conflict checking)
+  - **Filters out `*.cs` files** (C# files are excluded from merge conflict checking to avoid false positives from C# build-generated files, which may contain patterns resembling merge conflict markers)
+  - Skips binary/unreadable files
+  - Skips directories
+- **Empty File List**: Gracefully handles cases where no files need checking (e.g., PRs that only delete files)
+
+## Example Output
+
+When conflict markers are detected:
+
+```
+❌ Merge conflict markers detected in the following files:
+  - src/example.cs
+    Markers found: <<<<<<<, =======, >>>>>>>
+  - README.md
+    Markers found: <<<<<<<, =======, >>>>>>>
-  - src/example.cs
-    Markers found: <<<<<<<, =======, >>>>>>>
-  - README.md
-    Markers found: <<<<<<<, =======, >>>>>>>
+  - README.md
+    Markers found: <<<<<<<, =======, >>>>>>>
+  - src/example.txt
+    Markers found: <<<<<<<, =======, >>>>>>>
-  - src/example.cs
-    Markers found: <<<<<<<, =======, >>>>>>>
-  - README.md
-    Markers found: <<<<<<<, =======, >>>>>>>
+  - README.md
+    Markers found: <<<<<<<, =======, >>>>>>>
+  - src/example.txt
+    Markers found: <<<<<<<, =======, >>>>>>>
+
+Please resolve these conflicts before merging.
+```
+
+When no markers are found:
+
+```
+✅ No merge conflict markers found
+```
+
+## Integration
+
+This action is integrated into the `linux-ci.yml` workflow and runs automatically on all pull requests to ensure code quality before merging.
@@ -0,0 +1,37 @@
+name: 'Check for Merge Conflict Markers'
+description: 'Checks for Git merge conflict markers in changed files for pull requests'
+author: 'PowerShell Team'
+
+outputs:
+  files-checked:
+    description: 'Number of files checked for merge conflict markers'
+    value: ${{ steps.check.outputs.files-checked }}
+  conflicts-found:
+    description: 'Number of files with merge conflict markers'
+    value: ${{ steps.check.outputs.conflicts-found }}
+
+runs:
+  using: 'composite'
+  steps:
+    - name: Get changed files
+      id: changed-files
+      uses: "./.github/actions/infrastructure/get-changed-files"
+
+    - name: Check for merge conflict markers
+      id: check
+      shell: pwsh
+      env:
+        CHANGED_FILES_JSON: ${{ steps.changed-files.outputs.files }}
+      run: |
+        # Get changed files from environment variable (secure against injection)
+        $changedFilesJson = $env:CHANGED_FILES_JSON
+        # Ensure we always have an array (ConvertFrom-Json returns null for empty JSON arrays)
+        $changedFiles = @($changedFilesJson | ConvertFrom-Json)
+
+        # Import ci.psm1 and run the check
+        Import-Module "$env:GITHUB_WORKSPACE/tools/ci.psm1" -Force
+        Test-MergeConflictMarker -File $changedFiles -WorkspacePath $env:GITHUB_WORKSPACE
+
+branding:
+  icon: 'alert-triangle'
+  color: 'red'
diff --git a/test/infrastructure/ciModule.Tests.ps1 b/test/infrastructure/ciModule.Tests.ps1
@@ -0,0 +1,246 @@
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+# NOTE: This test file tests the Test-MergeConflictMarker function which detects Git merge conflict markers.
+# IMPORTANT: Do NOT use here-strings or literal conflict markers (e.g., "<<<<<<<", "=======", ">>>>>>>")
+# in this file, as they will trigger conflict marker detection in CI pipelines.
+# Instead, use string multiplication (e.g., '<' * 7) to dynamically generate these markers at runtime.
+
+Describe "Test-MergeConflictMarker" {
+    BeforeAll {
+        # Import the module
+        Import-Module "$PSScriptRoot/../../tools/ci.psm1" -Force
+
+        # Create a temporary test workspace
+        $script:testWorkspace = Join-Path $TestDrive "workspace"
+        New-Item -ItemType Directory -Path $script:testWorkspace -Force | Out-Null
+
+        # Create temporary output files
+        $script:testOutputPath = Join-Path $TestDrive "outputs.txt"
+        $script:testSummaryPath = Join-Path $TestDrive "summary.md"
+    }
+
+    AfterEach {
+        # Clean up test files after each test
+        if (Test-Path $script:testWorkspace) {
+            Get-ChildItem $script:testWorkspace -File -ErrorAction SilentlyContinue | Remove-Item -Force -ErrorAction SilentlyContinue
+        }
+        Remove-Item $script:testOutputPath -Force -ErrorAction SilentlyContinue
+        Remove-Item $script:testSummaryPath -Force -ErrorAction SilentlyContinue
+    }
+
+    Context "When no files are provided" {
+        It "Should handle empty file array gracefully" {
+            # The function now accepts empty arrays to handle cases like delete-only PRs
+            $emptyArray = @()
+            Test-MergeConflictMarker -File $emptyArray -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "files-checked=0"
+            $outputs | Should -Contain "conflicts-found=0"
+
+            $summary = Get-Content $script:testSummaryPath -Raw
+            $summary | Should -Match "No Files to Check"
+        }
+    }
+
+    Context "When files have no conflicts" {
+        It "Should pass for clean files" {
+            $testFile = Join-Path $script:testWorkspace "clean.txt"
+            "This is a clean file" | Out-File $testFile -Encoding utf8
+
+            Test-MergeConflictMarker -File @("clean.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "files-checked=1"
+            $outputs | Should -Contain "conflicts-found=0"
+
+            $summary = Get-Content $script:testSummaryPath -Raw
+            $summary | Should -Match "No Conflicts Found"
+        }
+    }
+
+    Context "When files have conflict markers" {
+        It "Should detect <<<<<<< marker" {
+            $testFile = Join-Path $script:testWorkspace "conflict1.txt"
+            "Some content`n" + ('<' * 7) + " HEAD`nConflicting content" | Out-File $testFile -Encoding utf8
+
+            { Test-MergeConflictMarker -File @("conflict1.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath } | Should -Throw
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "files-checked=1"
+            $outputs | Should -Contain "conflicts-found=1"
+        }
+
+        It "Should detect ======= marker" {
+            $testFile = Join-Path $script:testWorkspace "conflict2.txt"
+            "Some content`n" + ('=' * 7) + "`nMore content" | Out-File $testFile -Encoding utf8
+
+            { Test-MergeConflictMarker -File @("conflict2.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath } | Should -Throw
+        }
+
+        It "Should detect >>>>>>> marker" {
+            $testFile = Join-Path $script:testWorkspace "conflict3.txt"
+            "Some content`n" + ('>' * 7) + " branch-name`nMore content" | Out-File $testFile -Encoding utf8
+
+            { Test-MergeConflictMarker -File @("conflict3.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath } | Should -Throw
+        }
+
+        It "Should detect multiple markers in one file" {
+            $testFile = Join-Path $script:testWorkspace "conflict4.txt"
+            $content = "Some content`n" + ('<' * 7) + " HEAD`nContent A`n" + ('=' * 7) + "`nContent B`n" + ('>' * 7) + " branch`nMore content"
+            $content | Out-File $testFile -Encoding utf8
+
+            { Test-MergeConflictMarker -File @("conflict4.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath } | Should -Throw
+
+            $summary = Get-Content $script:testSummaryPath -Raw
+            $summary | Should -Match "Conflicts Detected"
+            $summary | Should -Match "conflict4.txt"
+        }
+
+        It "Should detect conflicts in multiple files" {
+            $testFile1 = Join-Path $script:testWorkspace "conflict5.txt"
+            ('<' * 7) + " HEAD" | Out-File $testFile1 -Encoding utf8
+
+            $testFile2 = Join-Path $script:testWorkspace "conflict6.txt"
+            ('=' * 7) | Out-File $testFile2 -Encoding utf8
+
+            { Test-MergeConflictMarker -File @("conflict5.txt", "conflict6.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath } | Should -Throw
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "files-checked=2"
+            $outputs | Should -Contain "conflicts-found=2"
+        }
+    }
+
+    Context "When markers are not at line start" {
+        It "Should not detect markers in middle of line" {
+            $testFile = Join-Path $script:testWorkspace "notconflict.txt"
+            "This line has <<<<<<< in the middle" | Out-File $testFile -Encoding utf8
+
+            Test-MergeConflictMarker -File @("notconflict.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "conflicts-found=0"
+        }
+
+        It "Should not detect markers with wrong number of characters" {
+            $testFile = Join-Path $script:testWorkspace "wrongcount.txt"
+            ('<' * 6) + " Only 6`n" + ('<' * 8) + " 8 characters" | Out-File $testFile -Encoding utf8
+
+            Test-MergeConflictMarker -File @("wrongcount.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "conflicts-found=0"
+        }
+    }
+
+    Context "When handling special file scenarios" {
+        It "Should skip non-existent files" {
+            Test-MergeConflictMarker -File @("nonexistent.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "files-checked=0"
+        }
+
+        It "Should handle absolute paths" {
+            $testFile = Join-Path $script:testWorkspace "absolute.txt"
+            "Clean content" | Out-File $testFile -Encoding utf8
+
+            Test-MergeConflictMarker -File @($testFile) -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "conflicts-found=0"
+        }
+
+        It "Should handle mixed relative and absolute paths" {
+            $testFile1 = Join-Path $script:testWorkspace "relative.txt"
+            "Clean" | Out-File $testFile1 -Encoding utf8
+
+            $testFile2 = Join-Path $script:testWorkspace "absolute.txt"
+            "Clean" | Out-File $testFile2 -Encoding utf8
+
+            Test-MergeConflictMarker -File @("relative.txt", $testFile2) -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Should -Contain "files-checked=2"
+            $outputs | Should -Contain "conflicts-found=0"
+        }
+    }
+
+    Context "When summary and output generation" {
+        It "Should generate proper GitHub Actions outputs format" {
+            $testFile = Join-Path $script:testWorkspace "test.txt"
+            "Clean file" | Out-File $testFile -Encoding utf8
+
+            Test-MergeConflictMarker -File @("test.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath
+
+            $outputs = Get-Content $script:testOutputPath
+            $outputs | Where-Object {$_ -match "^files-checked=\d+$"} | Should -Not -BeNullOrEmpty
+            $outputs | Where-Object {$_ -match "^conflicts-found=\d+$"} | Should -Not -BeNullOrEmpty
+        }
+
+        It "Should generate markdown summary with conflict details" {
+            $testFile = Join-Path $script:testWorkspace "marked.txt"
+            $content = "Line 1`n" + ('<' * 7) + " HEAD`nLine 3`n" + ('=' * 7) + "`nLine 5"
+            $content | Out-File $testFile -Encoding utf8
+
+            { Test-MergeConflictMarker -File @("marked.txt") -WorkspacePath $script:testWorkspace -OutputPath $script:testOutputPath -SummaryPath $script:testSummaryPath } | Should -Throw
+
+            $summary = Get-Content $script:testSummaryPath -Raw
+            $summary | Should -Match "# Merge Conflict Marker Check Results"
+            $summary | Should -Match "marked.txt"
+            $summary | Should -Match "\| Line \| Marker \|"
+        }
+    }
+}
+
+Describe "Install-CIPester" {
+    BeforeAll {
+        # Import the module
+        Import-Module "$PSScriptRoot/../../tools/ci.psm1" -Force
+    }
+
+    Context "When checking function exists" {
+        It "Should export Install-CIPester function" {
+            $function = Get-Command Install-CIPester -ErrorAction SilentlyContinue
+            $function | Should -Not -BeNullOrEmpty
+            $function.ModuleName | Should -Be 'ci'
+        }
+
+        It "Should have expected parameters" {
+            $function = Get-Command Install-CIPester
+            $function.Parameters.Keys | Should -Contain 'MinimumVersion'
+            $function.Parameters.Keys | Should -Contain 'MaximumVersion'
+            $function.Parameters.Keys | Should -Contain 'Force'
+        }
+
+        It "Should accept version parameters" {
+            $function = Get-Command Install-CIPester
+            $function.Parameters['MinimumVersion'].ParameterType.Name | Should -Be 'String'
+            $function.Parameters['MaximumVersion'].ParameterType.Name | Should -Be 'String'
+            $function.Parameters['Force'].ParameterType.Name | Should -Be 'SwitchParameter'
+        }
+    }
+
+    Context "When validating real execution" {
+        # These tests only run in CI where we can safely install/test Pester
+
+        It "Should successfully run without errors when Pester exists" {
+            if (!$env:CI) {
+                Set-ItResult -Skipped -Because "Test requires CI environment to safely install Pester"
+            }
+
+            { Install-CIPester -ErrorAction Stop } | Should -Not -Throw
+        }
+
+        It "Should accept custom version parameters" {
+            if (!$env:CI) {
+                Set-ItResult -Skipped -Because "Test requires CI environment to safely install Pester"
+            }
+
+            { Install-CIPester -MinimumVersion '4.0.0' -MaximumVersion '5.99.99' -ErrorAction Stop } | Should -Not -Throw
+        }
+    }
+}
+