fix(bench): stabilize report column/row ordering across input permutations (#39)

- variants: use direct tuple comparison instead of format! string, add sort() after dedup
- Memory section: sort rows by (test_name, backend, variant) before output
- Extra Metrics section: sort rows by (test_name, variant_label) before output
- add [lib] target to Cargo.toml to enable unit tests
- add regression test: same data in different input order produces identical report

crates/bench/Cargo.toml

@@ -3,6 +3,10 @@ name = "log-viewer-bench"
 version = "0.1.0"
 edition = "2024"
 
+[lib]
+name = "log_viewer_bench"
+path = "src/lib.rs"
+
 [[bin]]
 name = "log-viewer-bench"
 path = "src/main.rs"

crates/bench/src/report.rs

@@ -43,14 +43,14 @@ pub fn format_report(results: &[BenchmarkResult]) -> String {
 
         let mut variants: Vec<(String, String)> = Vec::new();
         for r in category_results {
-            let key = format!("{} ({})", r.backend, r.variant);
             if !variants
                 .iter()
-                .any(|(b, v)| format!("{} ({})", b, v) == key)
+                .any(|(b, v)| b == &r.backend && v == &r.variant)
             {
                 variants.push((r.backend.clone(), r.variant.clone()));
             }
         }
+        variants.sort();
 
         report.push_str("### Latency\n\n");
         report.push_str("| Test |");
@@ -143,7 +143,13 @@ pub fn format_report(results: &[BenchmarkResult]) -> String {
             report.push_str("| Test | Variant | RSS | Peak RSS | Page Faults |\n");
             report.push_str("|------|---------|-----|----------|-------------|\n");
 
-            for r in category_results {
+            let mut mem_rows: Vec<&BenchmarkResult> =
+                category_results.iter().copied().collect();
+            mem_rows.sort_by(|a, b| {
+                (&a.test_name, &a.backend, &a.variant)
+                    .cmp(&(&b.test_name, &b.backend, &b.variant))
+            });
+            for r in mem_rows {
                 let variant_label = format!("{} ({})", r.backend, r.variant);
                 report.push_str(&format!(
                     "| {} | {} | {} | {} | {} |\n",
@@ -157,7 +163,7 @@ pub fn format_report(results: &[BenchmarkResult]) -> String {
             report.push('\n');
         }
 
-        let extras: Vec<(String, String, Vec<(String, f64)>)> = category_results
+        let mut extras: Vec<(String, String, Vec<(String, f64)>)> = category_results
             .iter()
             .filter(|r| !r.extra.is_empty())
             .map(|r| {
@@ -171,6 +177,7 @@ pub fn format_report(results: &[BenchmarkResult]) -> String {
                 )
             })
             .collect();
+        extras.sort_by(|a, b| (&a.0, &a.1).cmp(&(&b.0, &b.1)));
 
         if !extras.is_empty() {
             report.push_str("### Extra Metrics\n\n");
@@ -205,3 +212,50 @@ fn capitalize(s: &str) -> String {
         Some(f) => f.to_uppercase().chain(c).collect(),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashMap;
+
+    fn make_result(
+        category: &str,
+        test_name: &str,
+        backend: &str,
+        variant: &str,
+        latency_us: Vec<u64>,
+    ) -> BenchmarkResult {
+        BenchmarkResult {
+            category: category.to_string(),
+            test_name: test_name.to_string(),
+            backend: backend.to_string(),
+            variant: variant.to_string(),
+            latency_us,
+            rss_kb: 0,
+            rss_peak_kb: 0,
+            page_faults: 0,
+            extra: HashMap::new(),
+        }
+    }
+
+    #[test]
+    fn report_ordering_independent_of_input_order() {
+        let set_a = vec![
+            make_result("sequential", "read_1mb", "pread", "default", vec![100, 110, 105]),
+            make_result("sequential", "read_1mb", "mmap", "default", vec![80, 85, 90]),
+            make_result("sequential", "read_4kb", "pread", "default", vec![10, 12, 11]),
+            make_result("sequential", "read_4kb", "mmap", "default", vec![8, 9, 7]),
+        ];
+
+        let set_b = vec![
+            make_result("sequential", "read_4kb", "mmap", "default", vec![8, 9, 7]),
+            make_result("sequential", "read_1mb", "mmap", "default", vec![80, 85, 90]),
+            make_result("sequential", "read_4kb", "pread", "default", vec![10, 12, 11]),
+            make_result("sequential", "read_1mb", "pread", "default", vec![100, 110, 105]),
+        ];
+
+        let report_a = format_report(&set_a);
+        let report_b = format_report(&set_b);
+        assert_eq!(report_a, report_b, "Reports must be identical regardless of input order");
+    }
+}