[tony-davis]

ISSUE ID: ROCm/rocm-libraries#11784

Problem

find_matched_subtrees() in configure_external_repo_ci.py truncates every changed file path to exactly 2 segments (category/name) before matching against registered subtree prefixes. This makes a nested subtree registered in repos-config.json (e.g. projects/hipblaslt/tensilelite, nested inside projects/hipblaslt) indistinguishable from a change to its parent: both collapse to projects/hipblaslt, silently losing the more specific match.

This blocks the companion synthetic-subprojects PR (#7998): even once TensileLite has its own consumer-graph node, change detection needs to be able to tell a TensileLite-only change apart from a hipblaslt-proper change in the first place.

Fix

Switch to longest-prefix-match: check registered prefixes from most to least specific, and attribute each changed file to exactly one (the longest matching) subtree.

def find_matched_subtrees(changed_files, valid_prefixes):
    prefixes_by_specificity = sorted(valid_prefixes, key=lambda p: p.count("/"), reverse=True)
    matched = set()
    for path in changed_files:
        segments = path.split("/")
        for prefix in prefixes_by_specificity:
            prefix_segments = prefix.split("/")
            if segments[: len(prefix_segments)] == prefix_segments:
                matched.add(prefix)
                break
    return sorted(matched)

A file nested in projects/hipblaslt/tensilelite/... now resolves to projects/hipblaslt/tensilelite (when that prefix is registered); a file elsewhere under projects/hipblaslt/... still resolves to projects/hipblaslt as before.

Testing

Added test_nested_subtree_wins_over_parent, test_parent_only_change_does_not_match_nested_subtree, and test_mixed_nested_and_parent_changes_match_both to build_tools/tests/configure_external_repo_ci_test.py, alongside the existing suite.

• python -m pytest build_tools/tests/configure_external_repo_ci_test.py -- 27 passed
• pre-commit run --files build_tools/github_actions/configure_external_repo_ci.py build_tools/tests/configure_external_repo_ci_test.py (black)

Tracked in ROCm/rocm-libraries#11784, alongside the companion synthetic-subprojects PR (#7998) and the rocm-libraries repos-config.json PR, which applies the identical fix to its own independently-duplicated copy of this function.

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[therock-pr-bot]

🎉 All checks passed! This PR is ready for review.

[Copilot]

🟢 Approval recommended

The longest-prefix-match implementation is straightforward, well-scoped, and is backed by targeted tests that cover the newly supported nested-subtree scenarios.

Pull request overview

This PR fixes external-repo CI subtree change detection in configure_external_repo_ci.py by switching from a fixed 2-segment truncation (category/name) to a longest-prefix-match algorithm, allowing nested registered subtrees (e.g. projects/hipblaslt/tensilelite) to be distinguished from parent subtree changes.

Changes:

• Implement longest-prefix match in find_matched_subtrees() so each changed file maps to the most-specific registered subtree prefix.
• Add unit tests covering nested-subtree vs parent-subtree matching behavior (nested wins; parent-only changes still match parent; mixed changes match both).

File summaries

File	Description
build_tools/github_actions/configure_external_repo_ci.py	Replaces fixed 2-segment subtree inference with longest-prefix matching over registered prefixes.
build_tools/tests/configure_external_repo_ci_test.py	Adds coverage for nested subtree matching and mixed parent/nested change scenarios.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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[newling]

LGTM

[geomin12]

lgtm thanks!