githubchanges.ps1

# Copyright (c) Microsoft Corporation.
# Licensed under the MIT License.

<#
.SYNOPSIS
    This script generates a list of changed files in the locally checked out branch and outputs
    that list to a file.
.DESCRIPTION
    Generates a file containing a list of all modified files (added/modified) in
    the checked out branch. The output file contains a list that is newline delimited, for
    example:

    Assets/MixedRealityToolkit.SDK/AssemblyInfo.cs
    Assets/MixedRealityToolkit.Tests/PlayModeTests/ManipulationHandlerTests.cs

    The file will not contain files that have been completely deleted (for example, if
    a change deleted Assets/MixedRealityToolkit.SDK/DeletedFile.cs), that line will not exist
    in the output file.

    Note that this script assumes that the local git repo doesn't already contain the
    target branch (e.g. main). This is what happens by default on Azure DevOps
    pipeline integrations with GitHub pull requests.

    In particular, this will checkout (via this command:
    git fetch --force --tags --prune --progress --no-recurse-submodules origin $(System.PullRequest.TargetBranch))
.EXAMPLE
    .\githubchanges.ps1 -OutputFile c:\path\to\changes\file.txt -RepoRoot c:\path\to\mrtk -TargetBranch main
#>
param(
    # The target branch that the pull request will merge into (e.g. main)
    [string]$TargetBranch,

    # The output filename (e.g. c:\path\to\output.txt)
    [Parameter(Mandatory = $true)]
    [string]$OutputFile,

    # The root folder of the repo (e.g. c:\repo)
    # This primarily used to filter out files that were deleted.
    [Parameter(Mandatory = $true)]
    [string]$RepoRoot
)

# The pull request ID might not be present (i.e. this is an adhoc build being spun up)
# and the target branch might not be set in which case there's nothing to validate.
if ([string]::IsNullOrWhiteSpace($TargetBranch)) {
    Write-Warning "TargetBranch isn't specified, skipping."
    exit 0;
}

# If the output file already exists, blow it away. Each run should get a new set of changed files.
if (Test-Path $OutputFile -PathType leaf) {
    Remove-Item $OutputFile
}
New-Item -ItemType File -Force -Path $OutputFile

# The path to the .git file is necessary when invoking the git command below, as the working
# directory may not actually be pointed toward the git path.
$gitDir = Join-Path -Path $RepoRoot -ChildPath ".git"

# Fetches the target branch so that the git diffing down below will actually be possible. git diff will list
# the set of changed files between two different commit stamps (or branches, in this case), and needs
# both branches to exist in order to make this happen.
# Uses a shallow fetch (i.e. depth=1) because only the latest commit from the target branch is
# needed to do the diff.
git --git-dir=$gitDir --work-tree=$RepoRoot fetch --depth=1 --force --tags --prune --progress --no-recurse-submodules origin $TargetBranch

# The set of changed files is the diff between the target branch and the pull request
# branch that was checked out locally.
$changedFiles = $(git --git-dir=$gitDir --work-tree=$RepoRoot diff --name-only ..origin/$TargetBranch 2>&1)

foreach ($changedFile in $changedFiles) {
    $joinedPath = Join-Path -Path $RepoRoot -ChildPath $changedFile
    # Only save the path if the file still exists - also, do not store the absolute path
    # of the file, in case this set of information is used later in the pipeline on a different
    # machine/context.
    if (Test-Path $joinedPath -PathType leaf) {
        Add-Content -Path $OutputFile -Value $changedFile
    }
}