perf: reuse Conda history while parsing environments (Fixes #475)

[Karthik Nadig (karthiknadig)]

Summary

• read conda-meta/history once per environment parse
• reuse the snapshot for manager discovery, Python package metadata, and environment naming
• preserve package JSON fallback when history is absent or incomplete
• add regression coverage that verifies one history-reader invocation

Validation

• cargo test -p pet-conda
• .\scripts\rust-precommit.ps1

Fixes #475

[github-actions]

Test Coverage Report (Linux)

Metric	Value
Current Coverage	80.5%
Base Branch Coverage	80.4%
Delta	.1% ✅

---

Coverage increased! Great work!

[github-actions]

Performance Report (Linux) ✅

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta	Change
Server Startup	1ms	1ms	0ms	1ms	N/A%
Full Refresh	48ms	254ms	50ms	-2ms	0%

Results based on 10 iterations. P50 = median, P95 = 95th percentile.

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Legend

• 🚀 Significant speedup (>100ms faster)
• ✅ Faster than baseline
• ➖ No significant change
• 🔺 Slower than baseline (>100ms)
• ⚠️ Significant slowdown (>500ms)

[github-actions]

Performance Report (macOS)

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta
Server Startup	103ms	10236ms	119ms	-16ms
Full Refresh	178ms	30293ms	282ms	-104ms

Results based on 10 iterations. P50 = median, P95 = 95th percentile.

---

Legend

• 🚀 Significant speedup (>100ms faster)
• ✅ Faster than baseline
• ➖ No significant change
• 🔺 Slower than baseline (>100ms)
• ⚠️ Significant slowdown (>500ms)

[github-actions]

Test Coverage Report (Windows)

Metric	Value
Current Coverage	77.31%
Base Branch Coverage	77.19%
Delta	0.12% ✅

---

Coverage increased! Great work!

[github-actions]

Performance Report (Windows) ➖

Metric	PR (P50)	PR (P95)	Baseline (P50)	Delta	Change
Server Startup	8ms	10ms	9ms	-1ms	-11.1%
Full Refresh	137ms	1487ms	137ms	0ms	0%

Results based on 10 iterations. P50 = median, P95 = 95th percentile.

---

Legend

• 🚀 Significant speedup (>100ms faster)
• ✅ Faster than baseline
• ➖ No significant change
• 🔺 Slower than baseline (>100ms)
• ⚠️ Significant slowdown (>500ms)

[Copilot]

Pull request overview

This PR reduces redundant synchronous I/O during Conda environment discovery by reading conda-meta/history once per environment parse and reusing that snapshot for multiple parsing steps. This aligns with PET’s performance goals by minimizing filesystem reads in hot discovery paths.

Changes:

• Read conda-meta/history once per CondaEnvironment parse and thread the contents through conda-dir detection, env naming, and Python package metadata extraction.
• Refactor CondaPackageInfo to accept optional pre-read history content and optimize history scanning (use reverse search instead of collecting matches).
• Add a regression test to ensure the environment-info path only invokes the history reader once.

Show a summary per file

File	Description
crates/pet-conda/src/package.rs	Adds history-reuse entry points for package parsing and avoids extra allocations when selecting the most recent matching history entry.
crates/pet-conda/src/environments.rs	Reads history once per env parse, reuses the creation line for conda-dir and name derivation, and adds a “reads history once” regression test.

Review details

Comments suppressed due to low confidence (2)

crates/pet-conda/src/environments.rs:410

• These tests now pass the entire history file contents into get_conda_env_name's creation_line parameter. That weakens the assertion because get_conda_env_name_from_creation_line is intended to receive only the filtered # cmd: ... create ... line; passing full history could accidentally match -n <name> in unrelated commands. Extract the creation line via get_conda_creation_line(&history) and pass as_deref() instead.

        let history = std::fs::read_to_string(&history_file).unwrap();
        let name = get_conda_env_name(&env_path, &conda_dir, Some(&history));

crates/pet-conda/src/environments.rs:490

• These tests now pass the entire history file contents into get_conda_env_name's creation_line parameter. That weakens the assertion because get_conda_env_name_from_creation_line is intended to receive only the filtered # cmd: ... create ... line; passing full history could accidentally match -n <name> in unrelated commands. Extract the creation line via get_conda_creation_line(&history) and pass as_deref() instead.

        let history = std::fs::read_to_string(&history_file).unwrap();
        let name = get_conda_env_name(&env_path, &conda_dir, Some(&history));

• Files reviewed: 2/2 changed files
• Comments generated: 2
• Review effort level: Low

[Copilot]

Review details

Comments suppressed due to low confidence (2)

crates/pet-conda/src/environments.rs:55

• This function reads conda-meta/history once for environment parsing, but the base environment can still cause a second read of the same file when manager discovery runs (e.g., CondaManager::from(prefix) calls get_conda_installation_used_to_create_conda_env(path), which reads history again when path is the conda install/base env). This means the PR’s stated “reuse … for manager discovery” / “one read per env per find()” goal isn’t fully met for the base env case.

Consider either (a) avoiding history reads in CondaManager::from when path is already a conda install (is_conda_install(path) fast-path), or (b) plumbing the already-read history/creation line into manager detection (or a per-refresh history cache) so manager lookup can reuse it.

pub fn get_conda_environment_info(
    env_path: &Path,
    manager: &Option<CondaManager>,
) -> Option<CondaEnvironment> {
    get_conda_environment_info_with_history_reader(env_path, manager, |env_path| {
        std::fs::read_to_string(env_path.join("conda-meta").join("history")).ok()
    })

crates/pet-conda/src/environments.rs:169

• get_conda_creation_line lowercases each candidate line using full Unicode case-folding (to_lowercase()), which is relatively expensive for a hot-path parser. Since the history format is ASCII, to_ascii_lowercase() is sufficient and avoids the heavier Unicode mapping.

    let line = history.lines().map(str::trim).find(|line| {
        let line = line.to_lowercase();
        line.starts_with("# cmd:") && line.contains(" create -")
    })?;

• Files reviewed: 2/2 changed files
• Comments generated: 0 new
• Review effort level: Low

[Copilot]

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0 new
• Review effort level: Low