bug(#631): match fails on empty substs

[maxonfjvipon]

Closes: #631

Summary by CodeRabbit

• Bug Fixes

  • CLI now explicitly reports an error when a pattern produces no substitutions, replacing the previous silent/debug-only behavior with clearer feedback.

• Tests

  • Added a test asserting that pattern-matching with no substitutions fails and emits an error, ensuring the new behavior is covered.

[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: 6bbd4d5a-22ae-4636-b330-ecdf733728e7

📥 Commits

Reviewing files that changed from the base of the PR and between 7389eb4 and 501c8da.

📒 Files selected for processing (1)

• test/CLISpec.hs

🚧 Files skipped from review as they are similar to previous changes (1)

• test/CLISpec.hs

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📝 Walkthrough

Walkthrough

runMatch now throws an EmptySubstsOnMatch CmdException when pattern matching produces no substitutions instead of only logging a debug message. A new exception constructor and Show message were added, and a test was added to assert the failing behavior.

Changes

Cohort / File(s)	Summary
CLI Types src/CLI/Types.hs	Added EmptySubstsOnMatch constructor to CmdException and updated its Show instance with message: "Provided pattern was not matched, no substitutions are built".
Match Runner src/CLI/Runners.hs	Changed runMatch to throw EmptySubstsOnMatch when substs is empty instead of emitting a debug log.
Tests test/CLISpec.hs	Added test "fails on empty substitutions" asserting the match command errors when no substitutions are produced.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• bug(#73): introduced match CLI command #468: Related CLI match implementation and handling of empty substitution lists; changes here build on that behavior.

Poem

🐰 I hopped through patterns, light and spry,
Found no carrots where they lie,
I thumped my foot, declared a fuss,
"EmptySubstsOnMatch" — hop, we must! 🥕

🚥 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 PR title accurately describes the main change: fixing the match command to fail when empty substitutions are produced.
Linked Issues check	✅ Passed	The changes implement the requirement from issue #631: the match command now fails (throws EmptySubstsOnMatch exception) when no substitutions are found instead of silently succeeding.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to addressing issue #631: adding the exception type, throwing it when substitutions are empty, and testing the behavior.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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• Create PR with unit tests

📝 Coding Plan

• Generate coding plan for human review comments

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@test/CLISpec.hs`:
- Around line 1030-1035: Remove the trailing whitespace at the end of the
withStdin argument in the test case labeled "fails on empty substitutions" so
the line containing withStdin "{Q.x.y}" has no extra spaces after the closing
brace; this fixes the fourmolu/formatter failure referenced in the test using
testCLIFailed and withStdin.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: d9f48d94-89a7-47a4-a2fb-bd84d1429058

📥 Commits

Reviewing files that changed from the base of the PR and between 56c980a and 7389eb4.

📒 Files selected for processing (3)

• src/CLI/Runners.hs
• src/CLI/Types.hs
• test/CLISpec.hs

[maxonfjvipon]

@rultor merge

[rultor]

@rultor merge

@maxonfjvipon OK, I'll try to merge now. You can check the progress of the merge here.

[rultor]

@rultor merge

@maxonfjvipon Done! FYI, the full log is here (took me 19min).

[0crat]

@maxonfjvipon Hey! Nice work on that contribution – you've bagged +12 points this time! 🎯 Here's the breakdown: +16 base points, but -4 for keeping it lean with just 10 hits-of-code (our policy encourages at least 40 for the full bonus). Still, quality over quantity – keep them coming! Your running score sits pretty at +122, and don't forget to peek at your Zerocracy account for the latest updates.