Add --max-syntax-highlighting-length (WIP)

src/cli.rs

@@ -734,14 +734,24 @@ pub struct Opt {
     /// insertion operations transforming one into the other.
     pub max_line_distance: f64,
 
-    #[arg(long = "max-line-length", default_value = "512", value_name = "N")]
+    #[arg(long = "max-line-length", default_value = "3000", value_name = "N")]
     /// Truncate lines longer than this.
     ///
-    /// To prevent any truncation, set to zero. Note that delta will be slow on very long lines
-    /// (e.g. minified .js) if truncation is disabled. When wrapping lines it is automatically set
-    /// to fit at least all visible characters.
+    /// To prevent any truncation, set to zero. When wrapping lines it is automatically overwritten
+    /// to fit at least all visible characters, see `--wrap-max-lines`.
     pub max_line_length: usize,
 
+    #[arg(
+        long = "max-syntax-highlighting-length",
+        default_value = "400",
+        value_name = "N"
+    )]
+    /// Stop syntax highlighting lines after this length.
+    ///
+    /// To highlighting the entire line, set to zero - but note that delta will be slow on very long
+    /// lines (e.g. minified .js).
+    pub max_syntax_length: usize,
+
     #[arg(
         long = "merge-conflict-begin-symbol",
         default_value = "▼",

src/config.rs

@@ -101,6 +101,7 @@ pub struct Config {
     pub max_line_distance_for_naively_paired_lines: f64,
     pub max_line_distance: f64,
     pub max_line_length: usize,
+    pub max_syntax_length: usize,
     pub merge_conflict_begin_symbol: String,
     pub merge_conflict_ours_diff_header_style: Style,
     pub merge_conflict_theirs_diff_header_style: Style,
@@ -392,6 +393,7 @@ impl From<cli::Opt> for Config {
             } else {
                 opt.max_line_length
             },
+            max_syntax_length: opt.max_syntax_length,
             merge_conflict_begin_symbol: opt.merge_conflict_begin_symbol,
             merge_conflict_ours_diff_header_style: styles["merge-conflict-ours-diff-header-style"],
             merge_conflict_theirs_diff_header_style: styles

src/options/set.rs

@@ -174,6 +174,7 @@ pub fn set_options(
             map_styles,
             max_line_distance,
             max_line_length,
+            max_syntax_length,
             // Hack: minus-style must come before minus-*emph-style because the latter default
             // dynamically to the value of the former.
             merge_conflict_begin_symbol,

src/paint.rs

@@ -696,11 +696,33 @@ pub fn get_syntax_style_sections_for_lines<'a>(
     ) {
         (Some(highlighter), true) => {
             for (line, _) in lines.iter() {
-                line_sections.push(
-                    highlighter
-                        .highlight_line(line, &config.syntax_set)
-                        .unwrap(),
-                );
+                if line.len() < config.max_syntax_length || config.max_syntax_length == 0 {
+                    line_sections.push(
+                        highlighter
+                            .highlight_line(line, &config.syntax_set)
+                            .unwrap(),
+                    );
+                } else {
+                    // Detailed ansi vs ascii length does not matter here, but this means the
+                    // result is not cut at exactly the requested position.
+                    let line_syntax = ansi::truncate_str(line, config.max_syntax_length, "");
+                    // re-split to get references into `line` with correct lifetimes.
+                    // SAFETY: slicing the string is safe because `truncate_str` only
+                    // cuts at grapheme borders, and nothing (`tail=""`) is added.
+                    let (with_syntax, plain) = line.split_at(line_syntax.len());
+                    line_sections.push(
+                        highlighter
+                            .highlight_line(with_syntax, &config.syntax_set)
+                            .unwrap(),
+                    );
+
+                    if !plain.is_empty() {
+                        line_sections
+                            .last_mut()
+                            .unwrap()
+                            .push((config.null_syntect_style, plain));
+                    }
+                }
             }
         }
         _ => {

src/tests/test_example_diffs.rs

@@ -1994,6 +1994,44 @@ src/align.rs:71: impl<'a> Alignment<'a> { │
             .expect_after_header("#partial\n\nremoved: a");
     }
 
+    #[test]
+    fn test_lines_with_syntax_width_limit() {
+        let result = DeltaTest::with_args(&[
+            "--max-line-length=42",
+            "--max-syntax-highlighting-length=18",
+        ])
+        .explain_ansi()
+        .with_input(GIT_DIFF_SINGLE_HUNK);
+        assert_snapshot!(result.output, @r###"
+        (normal)commit 94907c0f136f46dc46ffae2dc92dca9af7(reverse normal)→(normal)
+        Author: Dan Davison <[email protected](reverse normal)→(normal)
+        Date:   Thu May 14 11:13:17 2020 -0400
+
+            rustfmt
+
+
+        (blue)src/align.rs(normal)
+        (blue)───────────────────────────────────────────(normal)
+
+        (blue)─────────────────────────────(blue)┐(normal)
+        (blue)71(normal):(231) (81)impl(231)<(203)'a(231)> (149)Alignmen(normal)t<'a> { (blue)│(normal)
+        (blue)─────────────────────────────(blue)┘(normal)
+
+        (231)        (203)for(231) (i, x_(normal)i) in self.x.iter().en→
+        (231)            (203)for(231) (j(normal), y_j) in self.y.iter(→
+        (normal 52)                let (left, diag, up) =(normal 124) ((normal)
+        (normal 52)                    self.index(i, j + 1(normal 124)),(normal)
+        (normal 52)                    self.index(i, j),(normal)
+        (normal 52)                    self.index(i + 1, j),(normal)
+        (normal 52)                );(normal)
+        (231 22)                le(normal 22)t (left, diag, up) =(normal)
+        (231 22)                  (normal 22)  (normal 28)((normal 22)self.index(i, j + 1(normal 28)→(normal)
+        (231)                le(normal)t candidates = [
+        (231)                  (normal)  Cell {
+        (231)                  (normal)      parent: left,
+        "###);
+    }
+
     const GIT_DIFF_SINGLE_HUNK: &str = "\
 commit 94907c0f136f46dc46ffae2dc92dca9af7eb7c2e
 Author: Dan Davison <[email protected]>