Fix duplicate DOCS entries when asciidoctor is present

[jnasbyupgrade]

Problem

When asciidoctor is installed, make install fails with:

/usr/bin/install: will not overwrite just-created '.../object_reference.html' with './/doc/object_reference.html'

DOCS ends up containing doc/object_reference.html twice:

1. Line 23 of pgxntool/base.mk: $(wildcard doc/*) picks up the committed .html file
2. Line 135: DOCS += $(ASCIIDOC_HTML) adds the same path again as a generated asciidoc target

Both paths expand to the same filename, so install receives it twice in one invocation and refuses to overwrite a file it just wrote.

Fix

Use $(filter-out) to remove any ASCIIDOC_HTML files already present in DOCS before appending, then $(sort) to deduplicate. This is the same approach already taken in Postgres-Extensions/pgxntool 2.x.

Reproducer

Any project that commits its generated .html doc alongside its .adoc source, with asciidoctor in PATH.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 87700535-cbde-4a9d-bac8-b10180d2601c

📥 Commits

Reviewing files that changed from the base of the PR and between d191ef1 and 259e663.

📒 Files selected for processing (1)

• pgxntool/base.mk

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📝 Walkthrough

Walkthrough

The PR modifies a single makefile variable assignment in pgxntool/base.mk. When Asciidoc is available, the DOCS variable is now rebuilt as a sorted de-duplicated union of existing entries and generated Asciidoc HTML targets, using filter-out to prevent duplicate targets. This replaces the prior unconditional append behavior that could introduce duplicate HTML files in the documentation build target list.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Poem

A makefile once doubled its HTML with haste,
Now filters and sorts—no duplicates to waste.
One line of logic, so neat and so clean,
Deduplication, the best we've seen! 🐰✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly and concisely describes the main fix: preventing duplicate DOCS entries when asciidoctor is present, which matches the core change in the changeset.
Description check	✅ Passed	The description is well-related to the changeset, explaining the problem (duplicate HTML paths causing install failures), the root cause, the fix applied, and includes a reproducer scenario.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-docs-duplicate-html

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[jnasbyupgrade]

The correct fix is to update pgxntool, not hack it.