Use Cow in format_breaks

[leynos]

Summary

• avoid cloning unchanged lines when formatting thematic breaks
• convert CLI path to handle Cow<str> outputs
• update tests for new return type

Testing

• make fmt
• make lint
• make test

---

https://chatgpt.com/codex/tasks/task_e_68784ce217488322a5f4ac92ae30fe63

Summary by Sourcery

Refactor format_breaks to use Cow for improved efficiency and update related code and tests to accommodate the new return type.

Enhancements:

• Optimize format_breaks to avoid unnecessary cloning by returning Cow instead of String.

Tests:

• Update unit and integration tests to handle the new Cow return type from format_breaks.

[sourcery-ai]

Reviewer's Guide

This pull request refactors the format_breaks function to use Cow instead of cloning unchanged lines, updates the CLI and tests to accommodate the new return type, and improves efficiency by reducing unnecessary allocations.

Class diagram for format_breaks function refactor to Cow

classDiagram
    class format_breaks {
        +format_breaks(lines: &[String]) -> Vec<Cow<'_, str>>
    }
    class Cow {
        <<enum>>
        +Borrowed(&'a str)
        +Owned(String)
    }
    format_breaks --> Cow : returns Vec<Cow<'_, str>>

Loading

File-Level Changes

Change	Details	Files
Refactor format_breaks to return Vec<Cow> for efficiency.	Change return type from Vec to Vec<Cow>. Use Cow::Borrowed for unchanged lines and Cow::Owned for formatted breaks. Avoid unnecessary cloning of unchanged lines.	src/breaks.rs
Update CLI integration to handle Cow outputs from format_breaks.	Convert Cow outputs to owned Strings after formatting in process_lines.	src/main.rs
Update unit and integration tests for new Cow return type.	Adjust expected values in tests to use Cow instead of String. Update assertions to compare Vec<Cow> results.	src/breaks.rs tests/integration.rs

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[coderabbitai]

Summary by CodeRabbit

• Refactor
  • Improved internal handling of string data to optimise memory usage and performance. No changes to visible features or user experience.
• Tests
  • Updated tests to align with internal improvements in string handling. No impact on test coverage or outcomes.

Walkthrough

Update the format_breaks function to return a vector of Cow<str> for more efficient memory usage, replacing previous String allocations with borrowed references where possible. Adjust the main processing logic and all related test cases to accommodate the new return type and ensure correct ownership semantics.

Changes

File(s)	Change Summary
src/breaks.rs	Refactor format_breaks to return Vec<Cow<str>> instead of Vec<String>. Update internals to use Cow::Borrowed and add necessary imports.
src/main.rs	Update handling of format_breaks output: convert Cow<str> elements to owned String values before assignment. No logic changes.
tests/integration.rs	Update test cases to expect and compare Vec<Cow<str>> results, importing Cow and adjusting assertions accordingly.

Sequence Diagram(s)

sequenceDiagram
    participant Main as main.rs
    participant Breaks as breaks.rs
    participant Tests as integration.rs

    Main->>Breaks: format_breaks(&out) // returns Vec<Cow<str>>
    Breaks-->>Main: Vec<Cow<str>>
    Main->>Main: Map Cow<str> to String (into_owned)
    Main-->>Main: out = Vec<String>
    Tests->>Breaks: format_breaks(test_input)
    Breaks-->>Tests: Vec<Cow<str>>
    Tests-->>Tests: Compare with expected Vec<Cow<str>>

Loading

Possibly related PRs

• Add thematic break formatting #57: Originally introduced the format_breaks function and its thematic break normalisation, which this PR now refactors for improved efficiency.

Poem

In the land of Cow and String,
Borrowed lines now softly sing.
Out with clones, in with grace,
Memory saved, a tidy space.
Tests and main now heed the call—
Cow’s the hero, after all!
🐮✨

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📜 Recent review details

Configuration used: CodeRabbit UI
Review profile: ASSERTIVE
Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 7e198b0 and e68848c.

📒 Files selected for processing (3)

• src/breaks.rs (5 hunks)
• src/main.rs (2 hunks)
• tests/integration.rs (6 hunks)

🧰 Additional context used

📓 Path-based instructions (1)

**/*.rs

Instructions used from:

Sources:
⚙️ CodeRabbit Configuration File

🧬 Code Graph Analysis (2)

src/main.rs (1)

src/breaks.rs (1)

• format_breaks (19-38)

src/breaks.rs (1)

src/wrap.rs (1)

• is_fence (107-107)

🔇 Additional comments (12)

src/breaks.rs (7)

3-3: Import addition looks good.

The std::borrow::Cow import is correctly added to support the new return type.

---

19-19: Function signature change is correct.

The return type properly uses Vec<Cow<'_, str>> with appropriate lifetime annotation.

---

26-26: Cow::Borrowed usage is optimal.

Using Cow::Borrowed(line.as_str()) correctly avoids unnecessary string cloning for unchanged lines.

Also applies to: 33-33

---

31-31: Thematic break line usage is efficient.

Using Cow::Borrowed(THEMATIC_BREAK_LINE.as_str()) correctly avoids cloning the static string, addressing the previous performance suggestion.

---

42-42: Test import addition is correct.

The std::borrow::Cow import is properly added to support the updated test expectations.

---

52-56: Test expectations correctly updated.

The expected vector properly uses Vec<Cow<str>> with appropriate conversions for borrowed and owned forms.

---

66-67: Test conversion is clean and correct.

Using input.iter().map(|s| s.as_str().into()).collect() properly converts strings to Cow<str> for the test expectation.

tests/integration.rs (3)

1-1: Import addition is correct.

Adding borrow::Cow to the std imports is necessary for the updated test expectations.

---

1039-1043: Test expectations are properly updated.

Using Cow::Owned for the generated thematic break and into() conversions for input strings correctly matches the new return type.

---

1053-1054: All test expectation updates are consistent.

The pattern of converting to Vec<Cow<str>> is correctly applied across all format_breaks test functions.

Also applies to: 1063-1064, 1073-1073, 1083-1083

src/main.rs (2)

2-2: Import addition is appropriate.

Adding borrow::Cow to the std imports is necessary for the conversion logic.

---

46-49: Conversion logic is correct and efficient.

Using Cow::into_owned properly converts the result back to Vec<String> whilst maintaining the performance benefits of the optimization.

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---

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[sourcery-ai]

Hey @leynos - I've reviewed your changes and they look great!

Prompt for AI Agents

Please address the comments from this code review:
## Individual Comments

### Comment 1
<location> `src/breaks.rs:31` </location>
<code_context>

         if !in_code && THEMATIC_BREAK_RE.is_match(line.trim_end()) {
-            out.push(THEMATIC_BREAK_LINE.clone());
+            out.push(Cow::Owned(THEMATIC_BREAK_LINE.clone()));
         } else {
-            out.push(line.clone());
</code_context>

<issue_to_address>
Cloning THEMATIC_BREAK_LINE for each thematic break may be inefficient.

Consider using Cow::Borrowed(THEMATIC_BREAK_LINE.as_str()) to avoid unnecessary allocations, since THEMATIC_BREAK_LINE is static.
</issue_to_address>

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[leynos]

@coderabbitai review

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