Infinite recursion risk in ToolchainDiscoverer.getCanonicalPath() for root paths

[elharo]

Summary

ToolchainDiscoverer.getCanonicalPath() has a recursive fallback that can cause infinite recursion or stack overflow for root paths where path.getParent() returns null.

Location

ToolchainDiscoverer.java:267-273

https://github.com/apache/maven-toolchains-plugin/blob/master/src/main/java/org/apache/maven/plugins/toolchain/jdk/ToolchainDiscoverer.java#L267-L273

Code

private static Path getCanonicalPath(Path path) {
    try {
        return path.toRealPath();
    } catch (IOException e) {
        return getCanonicalPath(path.getParent()).resolve(path.getFileName());
    }
}

Problem

1. If path is a root directory (e.g. / on Linux or C:\ on Windows), path.getParent() returns null. The recursive call getCanonicalPath(null) throws NPE.
2. If path.getParent() itself fails with IOException, this creates infinite recursion leading to stack overflow.
3. The recursive approach also has no depth limit, so deeply nested paths that fail toRealPath() will recurse until stack overflow.

Impact

JDK discovery scanning directories like / or other root-relative paths could crash Maven with a stack overflow or NPE instead of gracefully skipping the problematic path.

Suggested Fix

Replace recursion with iteration:

private static Path getCanonicalPath(Path path) {
    try {
        return path.toRealPath();
    } catch (IOException e) {
        Path parent = path.getParent();
        if (parent == null) {
            return path;
        }
        return getCanonicalPath(parent).resolve(path.getFileName());
    }
}

Or better, use a non-recursive loop with null checks to eliminate the recursion entirely.