Add --max-syntax-highlighting-length, set to 400

--max-line-length increased to 3000, highlighting now stops after 400
characters. In that case the highlighting may be incorrect until it
is reset for the next hunk.

src/cli.rs

@@ -734,12 +734,22 @@ 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-syntax-highlighting-length",
+        default_value = "400",
+        value_name = "N"
+    )]
+    /// Stop syntax highlighting lines after this many characters.
+    ///
+    /// To always highlight entire lines, 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 = "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 this does nothing as it is
+    /// overwritten to fit at least all visible characters, see `--wrap-max-lines`.
     pub max_line_length: usize,
 
     #[arg(

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 +696,40 @@ 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(),
-                );
+                // Fast but simple length comparison. Overcounts non-printable ansi
+                // characters or wider UTF-8, but `truncate_str_short` in the
+                // else branch corrects that.
+                if line.len() < config.max_syntax_length || config.max_syntax_length == 0 {
+                    line_sections.push(
+                        highlighter
+                            .highlight_line(line, &config.syntax_set)
+                            .unwrap(),
+                    );
+                } else {
+                    let line_syntax = ansi::truncate_str_short(line, config.max_syntax_length);
+                    // Re-split to get references into `line` with correct lifetimes.
+                    // SAFETY: slicing the string is safe because `truncate_str_short` always
+                    // returns a prefix of the input and only cuts at grapheme borders.
+                    let (with_syntax, plain) = line.split_at(line_syntax.len());
+                    // Note: splitting a line and only feeding one half to the highlighter may
+                    // result in wrong highlighting until it is reset the next hunk.
+                    //
+                    // Also, as lines are no longer newline terminated they might not be
+                    // highlighted correctly, and because of lifetimes inserting '\n' here is not
+                    // possible, also see `prepare()`.
+                    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 +1994,149 @@ 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,
+        "###);
+    }
+
+    #[test]
+    fn test_lines_with_syntax_width_limit_wrapping() {
+        let result = DeltaTest::with_args(&[
+            "--side-by-side",
+            "--width=55",
+            "--wrap-max-lines=1",
+            "--max-line-length=10", // this gets ignored!
+            "--max-syntax-highlighting-length=22",
+        ])
+        .explain_ansi()
+        .with_input(GIT_DIFF_SINGLE_HUNK);
+
+        // eprintln!("{}", result.raw_output);
+        assert_snapshot!(result.output, @r###"
+        (normal)commit 94907c0f136f46dc46ffae2dc92dca9af7eb7c2e
+        Author: Dan Davison <[email protected]>
+        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)Alignment(231)<(203)'a(normal)> { (blue)│(normal)
+        (blue)─────────────────────────────(blue)┘(normal)
+
+        (blue)│(238) 71 (blue)│(231)        (203)for(231) (i, x_i)(blue)↵(blue) │(238) 71 (blue)│(231)        (203)for(231) (i, x_i)(blue)↵(normal)
+        (blue)│(238)    (blue)│(231) i(normal)n self.x.iter().en(reverse normal)→(blue) │(238)    (blue)│(231) i(normal)n self.x.iter().en(reverse normal)→(normal)
+        (blue)│(238) 72 (blue)│(231)            (203)for(231) (j, (blue)↵(blue) │(238) 72 (blue)│(231)            (203)for(231) (j, (blue)↵(normal)
+        (blue)│(238)    (blue)│(231)y_(normal)j) in self.y.iter((reverse normal)→(blue) │(238)    (blue)│(231)y_(normal)j) in self.y.iter((reverse normal)→(normal)
+        (blue)│(88) 73 (blue)│(231 52)                (81)let(231) (blue)↵(blue) │(28) 73 (blue)│(231 22)                (81)let(231) (blue)↵(normal)
+        (blue)│(88)    (blue)│(231 52)(l(normal 52)eft, diag, up) =(normal 124) ((normal 52) (blue) │(28)    (blue)│(231 22)(l(normal 22)eft, diag, up) =(normal)
+        (blue)│(88) 74 (blue)│(231 52)                    (blue)↵(blue) │(28) 74 (blue)│(231 22)                    (blue)↵(normal)
+        (blue)│(88)    (blue)│(231 52)se(normal 52)lf.index(i, j + 1),(blue) │(28)    (blue)│(231 28)((normal 22)s(normal 22)elf.index(i, j + 1(reverse normal)→(normal)
+        (blue)│(88) 75 (blue)│(231 52)                    (blue)↵(blue) │(28)    (blue)│(normal)
+        (blue)│(88)    (blue)│(231 52)se(normal 52)lf.index(i, j),(normal 52)    (blue) │(28)    (blue)│(normal)
+        (blue)│(88) 76 (blue)│(231 52)                    (blue)↵(blue) │(28)    (blue)│(normal)
+        (blue)│(88)    (blue)│(231 52)se(normal 52)lf.index(i + 1, j),(blue) │(28)    (blue)│(normal)
+        (blue)│(88) 77 (blue)│(231 52)                );(normal 52)   (blue) │(28)    (blue)│(normal)
+        (blue)│(238) 78 (blue)│(231)                (81)let(231) (blue)↵(blue) │(238) 75 (blue)│(231)                (81)let(231) (blue)↵(normal)
+        (blue)│(238)    (blue)│(231)ca(normal)ndidates = [       (blue) │(238)    (blue)│(231)ca(normal)ndidates = [
+        (blue)│(238) 79 (blue)│(231)                    (blue)↵(blue) │(238) 76 (blue)│(231)                    (blue)↵(normal)
+        (blue)│(238)    (blue)│(231)Ce(normal)ll {               (blue) │(238)    (blue)│(231)Ce(normal)ll {
+        (blue)│(238) 80 (blue)│(231)                    (blue)↵(blue) │(238) 77 (blue)│(231)                    (blue)↵(normal)
+        (blue)│(238)    (blue)│(231)  (normal)  parent: left,    (blue) │(238)    (blue)│(231)  (normal)  parent: left,
+        "###);
+    }
+
+    #[test]
+    fn test_lines_with_syntax_width_unicode() {
+        let result = DeltaTest::with_args(&["--max-syntax-highlighting-length=11"])
+            .explain_ansi()
+            .with_input(GIT_DIFF_ALL_UNICODE_W_FULLWIDTH);
+
+        assert_snapshot!(result.output, @r###"
+        (normal)
+
+        (blue)src/a(normal)
+        (blue)───────────────────────────────────────────(normal)
+
+        (blue)───(blue)┐(normal)
+        (blue)1(normal): (blue)│(normal)
+        (blue)───(blue)┘(normal)
+        (231)一æäöø€ÆÄÖ(normal)〇Øß一
+        (231)一æäöø€ÆÄÖ(normal)〇Øß一
+        (normal 52)二æäöø(normal 124)¢(normal 52)ÆÄÖ〇Øß二(normal)
+        (normal 52)二æäöø(normal 124)¢(normal 52)ÆÄÖ〇Øß二(normal)
+        (231 22)二æäöø(normal 28)€(normal 22)ÆÄÖ(normal 22)〇Øß二(normal)
+        (231 22)二æäöø(normal 28)€(normal 22)ÆÄÖ(normal 22)〇Øß二(normal)
+        (231)三æäöø€ÆÄÖ(normal)〇Øß三
+        (231)三æäöø€ÆÄÖ(normal)〇Øß三
+        (231)¶(normal)
+        "###);
+
+        let result = DeltaTest::with_args(&[
+            "--max-syntax-highlighting-length=10",
+            "--max-line-length=16",
+        ])
+        .explain_ansi()
+        .with_input(GIT_DIFF_ALL_UNICODE_W_FULLWIDTH);
+
+        // eprintln!("{}", result.raw_output);
+        assert_snapshot!(result.output, @r###"
+        (normal)
+
+        (blue)src/a(normal)
+        (blue)───────────────────────────────────────────(normal)
+
+        (blue)───(blue)┐(normal)
+        (blue)1(normal): (blue)│(normal)
+        (blue)───(blue)┘(normal)
+        (231)一æäöø€ÆÄÖ(normal)〇Øß→
+        (231)一æäöø€ÆÄÖ(normal)〇Øß→
+        (normal 52)二æäöø(normal 124)¢(normal 52)ÆÄÖ〇Øß→(normal)
+        (normal 52)二æäöø(normal 124)¢(normal 52)ÆÄÖ〇Øß→(normal)
+        (231 22)二æäöø(normal 28)€(normal 22)ÆÄÖ(normal 22)〇Øß→(normal)
+        (231 22)二æäöø(normal 28)€(normal 22)ÆÄÖ(normal 22)〇Øß→(normal)
+        (231)三æäöø€ÆÄÖ(normal)〇Øß→
+        (231)三æäöø€ÆÄÖ(normal)〇Øß→
+        (231)¶(normal)
+        "###);
+    }
+
     const GIT_DIFF_SINGLE_HUNK: &str = "\
 commit 94907c0f136f46dc46ffae2dc92dca9af7eb7c2e
 Author: Dan Davison <[email protected]>
@@ -2964,5 +3107,22 @@ Date:   Tue Jun 21 14:48:20 2022 +0200
 diff --git a a
 new file mode 100644
 index 0000000..e69de29
+";
+
+    const GIT_DIFF_ALL_UNICODE_W_FULLWIDTH: &str = "
+diff --git a/src/a b/src/a
+index 53f98b6..14d6caa 100644
+--- a/src/a
++++ b/src/a
+@@ -1,7 +1,7 @@
+ 一æäöø€ÆÄÖ〇Øß一
+ 一æäöø€ÆÄÖ〇Øß一
+-二æäöø¢ÆÄÖ〇Øß二
+-二æäöø¢ÆÄÖ〇Øß二
++二æäöø€ÆÄÖ〇Øß二
++二æäöø€ÆÄÖ〇Øß二
+ 三æäöø€ÆÄÖ〇Øß三
+ 三æäöø€ÆÄÖ〇Øß三
+ ¶
 ";
 }