[Backport 4.0.x] Avoid IllegalStateException on duplicate profile ids in DefaultModelBuilder

[ascheman]

Backport of #12419 to maven-4.0.x — clean cherry-pick of 67a94a1, no conflicts.

This fixes the MNG-8418 (#10209) regression on the rc-6 line: POMs with duplicate profile ids (e.g. javafx ≤ 20 with its OS-named profiles) crash dependency collection with IllegalStateException: Duplicate key from Collectors.toMap in DefaultModelBuilder.getProfileActivations. Maven 3 accepts these POMs; duplicate-id diagnostics remain with the validator.

This was also the root cause of the massembly-969 IT failure in maven-assembly-plugin's Maven 4 lane (apache/maven-assembly-plugin#1311) before the plugin worked around it by bumping to javafx 26 (apache/maven-assembly-plugin#1325) — real projects depending on older javafx POMs still hit it on rc-5.

Verified on this branch: DefaultModelBuilderTest 13/13 green (includes the new duplicate-profile-ids regression test).

🤖 Generated with Claude Code

[gnodet]

Review: [Backport 4.0.x] Avoid IllegalStateException on duplicate profile ids

Clean backport of #12419 to maven-4.0.x. The fix is the same logic, correctly adapted for Maven 4's immutable model API.

What this PR does well

• Correct fix — replaces Collectors.toMap(Profile::getId, ...) (which throws IllegalStateException on duplicate keys) with a position-indexed List<Activation>. The injectProfileActivations method is updated to iterate by index, preserving the 1:1 correspondence between profiles and their activations regardless of duplicate IDs.
• Proper null handling — getProfileActivations() now maps all profiles (including those without activations), but the if (activation != null) guard in injectProfileActivations correctly skips profiles without activations.
• Good test — testDuplicateProfileIdsRetainActivations() verifies two profiles with the same "default" ID coexist and each retains its distinct activation (one activeByDefault, one property-based).
• Excellent PR description — documents the real-world impact (javafx ≤ 20 POMs, massembly-969 IT failure) and links to the upstream fix.

Checklist

Check	Status
Tests	✓ New regression test with test fixture POM
Docs	✓ PR body documents context and verification
Commit convention	✓
Public API / backward compat	✓ Private methods only; restores Maven 3 behavior
Security	N/A
CI	⏳ In progress (initial-build pending)

Note: CI is still running but the code is identical in logic to #12419 (which passed all CI and was approved). Approving based on code correctness.

LGTM.

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Reviewed with Claude Code on behalf of Guillaume Nodet. This review was generated by an AI agent and may contain inaccuracies; please verify all suggestions before applying.