Fix modifiedApps incremental builds for projects with external appFolders

[Groenbech96]

Summary

When incrementalBuilds.mode is set to modifiedApps and a project references app folders outside its own directory via ../ paths, unmodified apps are never downloaded from the baseline workflow run. Instead, every app is recompiled on every PR — even when only a single file changed.

The bug

Get-UnmodifiedAppsFromBaselineWorkflowRun needs to match entries from $settings.appFolders (project-relative paths) against $skipFolders (repo-relative paths). The old code assumed all resolved folder paths start with .\ and used SubString(2) to strip that prefix:

# Old code
$downloadAppFolders = @($settings.appFolders | Where-Object {
    $skipFolders -contains "$projectWithSeperator$($_.SubString(2))"
})

This works when apps live inside the project folder (paths like .\app), but breaks when apps live outside (paths like ..\..\..\src\Apps\SomeApp\App).

Toy example to illustrate

Consider a repo layout where a project at build/projects/MyProject references apps at src/:

repo/
  src/
    Apps/
      Invoicing/App/app.json      ← modified
      Reporting/App/app.json      ← unmodified
  build/
    projects/
      MyProject/
        .AL-Go/settings.json      ← appFolders: ["../../../src/Apps/*/App"]

After ResolveProjectFolders resolves the glob from the project directory, $settings.appFolders contains:

..\..\..\src\Apps\Invoicing\App
..\..\..\src\Apps\Reporting\App

Meanwhile, $skipFolders (from GetFoldersFromAllProjects, resolved from the repo root) contains:

src\Apps\Reporting\App

The old matching logic did:

Step	Value
$_.SubString(2) on ..\..\..\src\Apps\Reporting\App	\..\..\src\Apps\Reporting\App
Prepend project separator	build\projects\MyProject\..\..\src\Apps\Reporting\App
Compare with $skipFolders	src\Apps\Reporting\App
Match?	No — string comparison, not path resolution

The result: $downloadAppFolders is always empty → no artifacts downloaded from baseline → all apps recompiled.

For comparison, the standard layout (apps inside the project) works because paths start with .\:

Step	Value
$_.SubString(2) on .\app	app
Prepend project separator (empty for root project)	app
Compare with $skipFolders	app
Match?	Yes

The fix

Replace the SubString(2) hack with proper path resolution. A new helper ConvertTo-RepoRelativePath resolves each project-relative folder to an absolute path via Join-Path -Resolve, then strips the base folder prefix to produce a clean repo-relative path that matches $skipFolders exactly:

# New code
function ConvertTo-RepoRelativePath {
    param([string] $folder, [string] $projectPath, [string] $baseFolder)
    $fullPath = Join-Path $projectPath $folder -Resolve -ErrorAction SilentlyContinue
    if (-not $fullPath) { return $null }
    $normalizedBase = $baseFolder.TrimEnd([IO.Path]::DirectorySeparatorChar) + [IO.Path]::DirectorySeparatorChar
    if ($fullPath.StartsWith($normalizedBase, [StringComparison]::OrdinalIgnoreCase)) {
        return $fullPath.Substring($normalizedBase.Length)
    }
    return $null
}

This works for both layouts:

Layout	$settings.appFolders entry	Resolved absolute	Repo-relative	Matches $skipFolders?
Nested project	..\..\..\src\Apps\Reporting\App	D:\a\repo\src\Apps\Reporting\App	src\Apps\Reporting\App	Yes
Standard	.\app	D:\a\repo\app	app	Yes

Tests

Two new Pester tests added to DetermineProjectsToBuild.Test.ps1:

1. Nested project with ../ paths — creates a repo layout where apps are outside the project folder. Fails without the fix (Download appFolders: - None), passes with the fix.
2. Standard layout — apps inside the project folder. Passes both before and after (backwards compatibility).

Test plan

• New test fails on old code, passes on new code
• All 28 existing tests continue to pass
• Validate on a real BCApps PR build

[Copilot]

Pull request overview

This PR fixes incremental builds in modifiedApps mode for projects whose appFolders resolve to paths outside the project directory (via ../), ensuring unmodified apps can be downloaded from the baseline workflow run instead of always being rebuilt.

Changes:

• Replace brittle SubString(2)-based folder matching with a new helper that resolves project-relative folders and converts them to repo-relative paths for comparison.
• Add Pester coverage for both nested-project (../ paths) and standard (.\ paths) layouts to prevent regressions.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Actions/DetermineProjectsToBuild/DetermineProjectsToBuild.psm1	Fixes skip/download folder matching by resolving to absolute paths and converting to repo-relative paths before comparing with $skipFolders.
Tests/DetermineProjectsToBuild.Test.ps1	Adds two tests validating correct unmodified-app detection for external appFolders and standard in-project folders.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated no new comments.

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[mazhelez]

Tests are quite unreadable. What do you think about extracting the filtering into a separate function that could be tested easier?

[mazhelez]

@copilot Can you please add release notes.

Also, fix the PSScriptAnalyzer alerts.

[mazhelez]

@copilot Can you please add release notes.

Also, fix the PSScriptAnalyzer alerts.

@Groenbech96 can you please summon @copilot for a couple of more things?