Fix git-grep match-highlighting at line-start

This commit fixes highlighting the part of the line of code that matches
the git grep query in cases where the match starts at the beginning of
the lines.

Fixes #1056.

src/handlers/grep.rs

@@ -222,14 +222,14 @@ fn get_code_style_sections<'b>(
     non_match_style: Style,
     grep: &GrepLine,
 ) -> Option<StyleSectionSpecifier<'b>> {
-    if let Some(raw_code_start) = ansi::ansi_preserving_index(
+    if let Some(prefix_end) = ansi::ansi_preserving_index(
         raw_line,
         match grep.line_number {
-            Some(n) => format!("{}:{}:", grep.path, n).len(),
-            None => grep.path.len() + 1,
+            Some(n) => format!("{}:{}:", grep.path, n).len() - 1,
+            None => grep.path.len(),
         },
     ) {
-        let match_style_sections = ansi::parse_style_sections(&raw_line[raw_code_start..])
+        let match_style_sections = ansi::parse_style_sections(&raw_line[(prefix_end + 1)..])
             .iter()
             .map(|(ansi_term_style, s)| {
                 if ansi_term_style.foreground.is_some() {
@@ -900,4 +900,47 @@ mod tests {
         let apparently_grep_output = "src/co-7-fig.rs:xxx";
         assert_eq!(parse_grep_line(apparently_grep_output), None);
     }
+
+    #[test]
+    fn test_get_code_style_sections() {
+        use crate::ansi::strip_ansi_codes;
+        use crate::handlers::grep::get_code_style_sections;
+        use crate::paint::StyleSectionSpecifier;
+        use crate::style::Style;
+
+        let fake_parent_grep_command = "git --doesnt-matter grep --nor-this nor_this -- nor_this";
+        let _args = FakeParentArgs::for_scope(fake_parent_grep_command);
+
+        let miss = Style::new();
+        let hit = Style {
+            is_emph: true,
+            ..miss
+        };
+
+        let escape = "\x1B";
+        let working_example = format!("foo/bar/baz.yaml{escape}[36m:{escape}[m1090{escape}[36m:{escape}[m  - {escape}[1;31mkind: Service{escape}[mAccount");
+        let stripped = strip_ansi_codes(&working_example);
+        let grep = parse_grep_line(&stripped).unwrap();
+
+        assert_eq!(
+            get_code_style_sections(&working_example, hit, miss, &grep),
+            Some(StyleSectionSpecifier::StyleSections(vec![
+                (miss, "  - "),
+                (hit, "kind: Service"),
+                (miss, "Account")
+            ]))
+        );
+
+        let broken_example = format!("foo/bar/baz.yaml{escape}[36m:{escape}[m2{escape}[36m:{escape}[m{escape}[1;31mkind: Service{escape}[m");
+        let broken_stripped = strip_ansi_codes(&broken_example);
+        let broken_grep = parse_grep_line(&broken_stripped).unwrap();
+
+        assert_eq!(
+            get_code_style_sections(&broken_example, hit, miss, &broken_grep),
+            Some(StyleSectionSpecifier::StyleSections(vec![(
+                hit,
+                "kind: Service"
+            )]))
+        );
+    }
 }