Add support for Maven multi-module projects

[cowwoc]

What happened?

error: failed to discover plugin requirements: language host could not determine Pulumi packages: could not find ./mvnw, mvn on the $PATH: exec: "mvn": executable file not found in %PATH%

Example

1. Create a multi-module Maven project containing mvnw in the root
2. Place the pulumi-java project in a sub-module
3. Run pulumi up
4. Pulumi will complain:

error: failed to discover plugin requirements: language host could not determine Pulumi packages: could not find ./mvnw, mvn on the $PATH: exec: "mvn": executable file not found in %PATH%

Creating symbol links from the mvnw installation in the root module does not help (I get the same error). If I copy the files over, the error goes away, but obviously it's bad to maintain copies as they will fall out-of-sync.

Ideally, pulumi should scan the ancestor directories one at a time looking for mvnw and use the existing installation without needing a local copy or symbol link.

Output of pulumi about

CLI
Version      3.137.0
Go Version   go1.23.2
Go Compiler  gc

Host
OS       Microsoft Windows 10 Pro
Version  10.0.19045 Build 19045
Arch     x86_64

This project is written in java: executable='C:\Users\Gili\scoop\apps\openjdk\current\bin\java.exe' version='openjdk 23.0.1 2024-10-15
OpenJDK Runtime Environment (build 23.0.1+11-39)
OpenJDK 64-Bit Server VM (build 23.0.1+11-39, mixed mode, sharing)' java='C:\Users\Gili\scoop\apps\openjdk\current\bin\java.exe' javac='23.0.1'

Backend
Name           pulumi.com
URL            https://app.pulumi.com/cowwoc
User           cowwoc
Organizations  cowwoc, licensed-app
Token type     personal

No dependencies found

Pulumi locates its logs in C:\Users\Gili\AppData\Local\Temp by default
warning: Failed to get information about the plugin: failed to discover plugin requirements: language host could not determine Pulumi packages: could not find ./mvnw, mvn on the $PATH: exec: "mvn": executable file not found in %!P(MISSING)ATH%!(NOVERB)
warning: Failed to get information about the current stack: No current stack

Additional context

No response

Contributing

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[justinvp]

Ideally, pulumi should scan the ancestor directories one at a time looking for mvnw and use the existing installation without needing a local copy or symbol link.

Agreed. Something along the lines of what we do for Gradle:

pulumi-java/pkg/internal/executors/executor_gradle.go

Lines 58 to 82 in a34adb2

	func (gradle) findGradleRoot(workdir fsys.ParentFS) (fsys.ParentFS, string, error) {
	gradleRootMarkers := []string{
	"settings.gradle",
	"settings.gradle.kts",
	}
	d := workdir
	subproject := ""
	for {
	for _, p := range gradleRootMarkers {
	isGradleRoot, err := fsys.FileExists(d, p)
	if err != nil {
	return nil, subproject, err
	}
	if isGradleRoot {
	return d, subproject, nil
	}
	}
	if !d.HasParent() {
	// Abort search and assume workdir is the root
	return workdir, subproject, nil
	}
	subproject = fmt.Sprintf(":%s%s", d.Base(), subproject)
	d = d.Parent()
	}
	}