From 327323ad25d126f6394f26e1442667647022c383 Mon Sep 17 00:00:00 2001
From: Aleksey Kladov <aleksey.kladov@gmail.com>
Date: Tue, 13 Apr 2021 12:49:10 +0300
Subject: internal: fix flakiness of accidentally quadratic test

---
 crates/ide/src/syntax_highlighting/tests.rs | 98 +++++------------------------
 1 file changed, 17 insertions(+), 81 deletions(-)

(limited to 'crates/ide/src/syntax_highlighting')

diff --git a/crates/ide/src/syntax_highlighting/tests.rs b/crates/ide/src/syntax_highlighting/tests.rs
index b4818060f..933cfa6f3 100644
--- a/crates/ide/src/syntax_highlighting/tests.rs
+++ b/crates/ide/src/syntax_highlighting/tests.rs
@@ -2,8 +2,7 @@ use std::time::Instant;
 
 use expect_test::{expect_file, ExpectFile};
 use ide_db::SymbolKind;
-use stdx::format_to;
-use test_utils::{bench, bench_fixture, skip_slow_tests};
+use test_utils::{bench, bench_fixture, skip_slow_tests, AssertLinear};
 
 use crate::{fixture, FileRange, HlTag, TextRange};
 
@@ -266,90 +265,27 @@ fn syntax_highlighting_not_quadratic() {
         return;
     }
 
-    let mut measures = Vec::new();
-    for i in 6..=10 {
-        let n = 1 << i;
-        let fixture = bench_fixture::big_struct_n(n);
-        let (analysis, file_id) = fixture::file(&fixture);
+    let mut al = AssertLinear::default();
+    while al.next_round() {
+        for i in 6..=10 {
+            let n = 1 << i;
 
-        let time = Instant::now();
+            let fixture = bench_fixture::big_struct_n(n);
+            let (analysis, file_id) = fixture::file(&fixture);
 
-        let hash = analysis
-            .highlight(file_id)
-            .unwrap()
-            .iter()
-            .filter(|it| it.highlight.tag == HlTag::Symbol(SymbolKind::Struct))
-            .count();
-        assert!(hash > n as usize);
+            let time = Instant::now();
 
-        let elapsed = time.elapsed();
-        measures.push((n as f64, elapsed.as_millis() as f64))
-    }
+            let hash = analysis
+                .highlight(file_id)
+                .unwrap()
+                .iter()
+                .filter(|it| it.highlight.tag == HlTag::Symbol(SymbolKind::Struct))
+                .count();
+            assert!(hash > n as usize);
 
-    assert_linear(&measures)
-}
-
-/// Checks that a set of measurements looks like a linear function rather than
-/// like a quadratic function. Algorithm:
-///
-/// 1. Linearly scale input to be in [0; 1)
-/// 2. Using linear regression, compute the best linear function approximating
-///    the input.
-/// 3. Compute RMSE and  maximal absolute error.
-/// 4. Check that errors are within tolerances and that the constant term is not
-///    too negative.
-///
-/// Ideally, we should use a proper "model selection" to directly compare
-/// quadratic and linear models, but that sounds rather complicated:
-///
-///     https://stats.stackexchange.com/questions/21844/selecting-best-model-based-on-linear-quadratic-and-cubic-fit-of-data
-fn assert_linear(xy: &[(f64, f64)]) {
-    let (mut xs, mut ys): (Vec<_>, Vec<_>) = xy.iter().copied().unzip();
-    normalize(&mut xs);
-    normalize(&mut ys);
-    let xy = xs.iter().copied().zip(ys.iter().copied());
-
-    // Linear regression: finding a and b to fit y = a + b*x.
-
-    let mean_x = mean(&xs);
-    let mean_y = mean(&ys);
-
-    let b = {
-        let mut num = 0.0;
-        let mut denom = 0.0;
-        for (x, y) in xy.clone() {
-            num += (x - mean_x) * (y - mean_y);
-            denom += (x - mean_x).powi(2);
+            let elapsed = time.elapsed();
+            al.sample(n as f64, elapsed.as_millis() as f64);
         }
-        num / denom
-    };
-
-    let a = mean_y - b * mean_x;
-
-    let mut plot = format!("y_pred = {:.3} + {:.3} * x\n\nx     y     y_pred\n", a, b);
-
-    let mut se = 0.0;
-    let mut max_error = 0.0f64;
-    for (x, y) in xy {
-        let y_pred = a + b * x;
-        se += (y - y_pred).powi(2);
-        max_error = max_error.max((y_pred - y).abs());
-
-        format_to!(plot, "{:.3} {:.3} {:.3}\n", x, y, y_pred);
-    }
-
-    let rmse = (se / xs.len() as f64).sqrt();
-    format_to!(plot, "\nrmse = {:.3} max error = {:.3}", rmse, max_error);
-
-    assert!(rmse < 0.05 && max_error < 0.1 && a > -0.1, "\nLooks quadratic\n{}", plot);
-
-    fn normalize(xs: &mut Vec<f64>) {
-        let max = xs.iter().copied().max_by(|a, b| a.partial_cmp(b).unwrap()).unwrap();
-        xs.iter_mut().for_each(|it| *it /= max);
-    }
-
-    fn mean(xs: &[f64]) -> f64 {
-        xs.iter().copied().sum::<f64>() / (xs.len() as f64)
     }
 }
 
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