[MNG-8129] Handle InvalidPathException for broken relativePath on Windows

[gnodet]

Summary

• Catch InvalidPathException in BuildPathSource.resolve() (new API) and FileModelSource.getRelatedSource() (compat) and return null, letting the caller fall through to repository-based parent resolution
• Adds tests for both code paths

Problem

Some POMs on Maven Central have <relativePath> set to a GAV coordinate instead of a filesystem path. For example, artemis-project-2.33.0.pom contains:

<relativePath>org.apache:apache</relativePath>

On Windows, colons are reserved for drive letters, so Path.resolve("org.apache:apache") throws InvalidPathException before any file-existence check can run. On Linux/macOS the same call succeeds (: is valid in paths), and the subsequent Files.isRegularFile() check returns false, so the invalid path is harmlessly ignored.

Approach

Catch InvalidPathException and return null — an invalid path obviously cannot point to an existing parent POM, so returning null is the correct semantic (no local parent found → fall through to repository resolution). This matches Maven 3.x behavior.

Closes #12738

🤖 Generated with Claude Code

[gnodet]

Clean backport of PR #12739 to master. Same well-scoped fix catching InvalidPathException in both the new API (BuildPathSource.resolve) and compat API (FileModelSource.getRelatedSource) paths, with tests for each.

Returning null is the right semantic — it means "no local parent found" and causes the model builder to fall through to repository-based parent resolution, matching Maven 3.x behavior.

Same minor nit as #12739: FileModelSourceTest.java line 80 uses fully-qualified org.junit.jupiter.api.Assertions.assertNull(result) instead of a static import (file already statically imports assertFalse, assertTrue, assumeTrue).

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Claude Code on behalf of gnodet

[gnodet]

Re-reviewed after new commit 0f2e9097 adding relativePath validation for illegal filesystem characters (MNG-8129).

Verdict: APPROVE ✅

The two commits together provide excellent defense-in-depth:

1. Commit 1 — catches InvalidPathException at resolution time to prevent crashes on Windows when relativePath contains illegal characters.
2. Commit 2 — adds early model validation that rejects illegal filesystem characters in relativePath before resolution is attempted.

Noteworthy design choices:

• The severity escalation via errOn31 is well-reasoned: produces a WARNING in compat mode (Maven 3 backward compatibility) and an ERROR in impl mode (Maven 4 strict validation).
• The validation placement differs appropriately between compat (validateRawModel) and impl (validateFileModel), matching each module's validation architecture.
• ILLEGAL_RELATIVE_PATH_CHARS correctly excludes \ and / since directory separators are legitimate in relative paths.

Minor style observation (non-blocking): The ILLEGAL_RELATIVE_PATH_CHARS constant is hardcoded as :"<>|?* rather than derived from ILLEGAL_FS_CHARS (as done in the 3.10.x counterpart PR #12742, which uses ILLEGAL_FS_CHARS.replace("\\", "").replace("/", "")). Both produce the same character set, but the derived approach is slightly more maintainable.

Tests cover all four code paths. Clean implementation.