fix(completion): make PowerShell tab completion work again

[clay-good]

Status: LGTM — reproduced, fixed, and verified with a real PowerShell 7.5.4 parser (18 parse errors → 0) and live tab completion.

Fixes #1293

What was wrong

openspec completion install generated a PowerShell script that failed to parse, so completions never worked for any PowerShell user. The generator emitted switch ($positionalIndex) { } with zero clauses for every command whose positional arguments are all path-typed (PowerShell completes paths natively, so those cases produce no clauses) — 18 such blocks in the current registry. An empty switch body is a hard syntax error in PowerShell (Missing condition in switch statement clause), and PowerShell parses the whole file before running it, so one bad block aborted the entire script.

How it was fixed

In generateIndexedPositionalCompletion, the case clauses are now built first; when no positional produces any completion, the whole positional-index block (the token-counting loop plus the switch) is skipped — it existed only to feed the switch, so this is behavior-equivalent and leaves no dead code. Commands with real positional completions are unchanged.

Replication / proof

Generate the script from the real command registry and parse it with PowerShell's own parser:

BEFORE fix: parse errors = 18
  first: Missing condition in switch statement clause. (line 106)
AFTER fix:  parse errors = 0

Dot-sourcing the fixed script in pwsh 7.5.4 and invoking TabExpansion2 returns real completions:

completions for 'openspec val': validate
completions for 'openspec completion ': generate, install, uninstall

Two regression tests added: a unit test for a path-only positional command, and a registry-wide test asserting the generated script never contains an empty switch ($positionalIndex) block. Full suite: 1,860 passed; the only failures are the 17 known environment-only zsh-installer failures on this machine (local oh-my-zsh; CI unaffected).

Notes

• bash/zsh/fish generators are untouched — empty case bodies are legal in those shells.
• Pre-existing and out of scope: with an empty command list the outer switch ($command) would also be empty, but the registry is static and never empty, so it's unreachable in practice.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Fixed PowerShell completion scripts failing to load when commands contained only path-based positional parameters.
  • Prevented generation of invalid empty PowerShell switch blocks.
  • Restored tab completion for affected commands.

• Tests

  • Added coverage to verify generated scripts omit empty positional completion switches and avoid unnecessary positional-index references.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 6168fa35-aee5-4e5a-9c08-fa88ba20c84b

📥 Commits

Reviewing files that changed from the base of the PR and between 0a99f41 and 9659f48.

📒 Files selected for processing (3)

• .changeset/fix-powershell-empty-switch.md
• src/core/completions/generators/powershell-generator.ts
• test/core/completions/generators/powershell-generator.test.ts

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📝 Walkthrough

Walkthrough

The PowerShell generator now omits empty positional-index switches. Tests cover commands with no positional completions and the actual command registry, while a changeset documents the fix.

Changes

PowerShell completion generation

Layer / File(s)	Summary
Skip empty positional completion switches src/core/completions/generators/powershell-generator.ts	Precomputes positional clauses, skips entries without completions, and avoids emitting an empty switch ($positionalIndex) block.
Validate generated PowerShell output test/core/completions/generators/powershell-generator.test.ts, .changeset/fix-powershell-empty-switch.md	Tests custom and registry-based generation, and documents the PowerShell completion fix.

Estimated code review effort: 2 (Simple) | ~10 minutes

Suggested reviewers: tabishb

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: fixing PowerShell tab completion by preventing parse-breaking empty switch blocks.
Linked Issues check	✅ Passed	The generator fix and regression tests address the linked issue by omitting empty PowerShell switch blocks and restoring completion parsing.
Out of Scope Changes check	✅ Passed	All changes are in-scope: generator logic, regression tests, and a changelog entry for the PowerShell completion fix.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/powershell-empty-switch

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_{Comment @coderabbitai help to get the list of available commands.}

[alfred-openspec]

Looks good. The fix is correctly scoped, preserves mixed positional indexing, and includes focused plus registry-wide regression coverage.