Support precision specifier in run-time format strings

2 files changed, 73 insertions, 9 deletions

diff --git a/src/features/line_numbers.rs b/src/features/line_numbers.rs
index 0cc4ebfb..7082d05d 100644
--- a/src/features/line_numbers.rs
+++ b/src/features/line_numbers.rs
@@ -266,14 +266,22 @@ fn format_and_paint_line_number_field<'a>(
             .as_ref()
             .unwrap_or(&Align::Center);
         match placeholder.placeholder {
-            Some(Placeholder::NumberMinus) => ansi_strings.push(styles[Minus].paint(
-                format_line_number(line_numbers[Minus], alignment_spec, width, None, config),
-            )),
+            Some(Placeholder::NumberMinus) => {
+                ansi_strings.push(styles[Minus].paint(format_line_number(
+                    line_numbers[Minus],
+                    alignment_spec,
+                    width,
+                    placeholder.precision,
+                    None,
+                    config,
+                )))
+            }
             Some(Placeholder::NumberPlus) => {
                 ansi_strings.push(styles[Plus].paint(format_line_number(
                     line_numbers[Plus],
                     alignment_spec,
                     width,
+                    placeholder.precision,
                     Some(plus_file),
                     config,
                 )))
@@ -292,10 +300,11 @@ fn format_line_number(
     line_number: Option<usize>,
     alignment: &Align,
     width: usize,
+    precision: Option<usize>,
     plus_file: Option<&str>,
     config: &config::Config,
 ) -> String {
-    let pad = |n| format::pad(n, width, alignment);
+    let pad = |n| format::pad(n, width, alignment, precision);
     match (line_number, config.hyperlinks, plus_file) {
         (None, _, _) => pad(""),
         (Some(n), true, Some(file)) => {
@@ -332,6 +341,7 @@ pub mod tests {
                 placeholder: Some(Placeholder::NumberMinus),
                 alignment_spec: None,
                 width: None,
+                precision: None,
                 suffix: "".into(),
                 prefix_len: 0,
                 suffix_len: 0,
@@ -348,6 +358,7 @@ pub mod tests {
                 placeholder: Some(Placeholder::NumberPlus),
                 alignment_spec: None,
                 width: Some(4),
+                precision: None,
                 suffix: "".into(),
                 prefix_len: 0,
                 suffix_len: 0,
@@ -364,6 +375,7 @@ pub mod tests {
                 placeholder: Some(Placeholder::NumberPlus),
                 alignment_spec: Some(Align::Right),
                 width: Some(4),
+                precision: None,
                 suffix: "".into(),
                 prefix_len: 0,
                 suffix_len: 0,
@@ -380,6 +392,7 @@ pub mod tests {
                 placeholder: Some(Placeholder::NumberPlus),
                 alignment_spec: Some(Align::Right),
                 width: Some(4),
+                precision: None,
                 suffix: "".into(),
                 prefix_len: 0,
                 suffix_len: 0,
@@ -396,6 +409,7 @@ pub mod tests {
                 placeholder: Some(Placeholder::NumberPlus),
                 alignment_spec: Some(Align::Right),
                 width: Some(4),
+                precision: None,
                 suffix: "@@".into(),
                 prefix_len: 2,
                 suffix_len: 2,
@@ -413,6 +427,7 @@ pub mod tests {
                     placeholder: Some(Placeholder::NumberMinus),
                     alignment_spec: Some(Align::Left),
                     width: Some(3),
+                    precision: None,
                     suffix: "@@---{np:_>4}**".into(),
                     prefix_len: 2,
                     suffix_len: 15,
@@ -422,6 +437,7 @@ pub mod tests {
                     placeholder: Some(Placeholder::NumberPlus),
                     alignment_spec: Some(Align::Right),
                     width: Some(4),
+                    precision: None,
                     suffix: "**".into(),
                     prefix_len: 5,
                     suffix_len: 2,
@@ -439,6 +455,7 @@ pub mod tests {
                 placeholder: None,
                 alignment_spec: None,
                 width: None,
+                precision: None,
                 suffix: "__@@---**".into(),
                 prefix_len: 0,
                 suffix_len: 9,
@@ -455,12 +472,14 @@ pub mod tests {
                 placeholder: Some(Placeholder::NumberMinus),
                 alignment_spec: Some(Align::Left),
                 width: Some(4),
+                precision: None,
                 suffix: "|".into(),
                 prefix_len: 2,
                 suffix_len: 1,
             }]
         );
     }
+
     #[test]
     fn test_line_number_format_odd_width_two() {
         assert_eq!(
@@ -475,6 +494,7 @@ pub mod tests {
                     placeholder: Some(Placeholder::NumberMinus),
                     alignment_spec: Some(Align::Left),
                     width: Some(4),
+                    precision: None,
                     suffix: "+{np:<4}|".into(),
                     prefix_len: 2,
                     suffix_len: 9,
@@ -484,6 +504,7 @@ pub mod tests {
                     placeholder: Some(Placeholder::NumberPlus),
                     alignment_spec: Some(Align::Left),
                     width: Some(4),
+                    precision: None,
                     suffix: "|".into(),
                     prefix_len: 1,
                     suffix_len: 1,
@@ -500,6 +521,7 @@ pub mod tests {
                 placeholder: None,
                 alignment_spec: None,
                 width: None,
+                precision: None,
                 suffix: "|++|".into(),
                 prefix_len: 1,
                 suffix_len: 4,
@@ -522,6 +544,7 @@ pub mod tests {
                 placeholder: Some(Placeholder::NumberMinus),
                 alignment_spec: None,
                 width: None,
+                precision: None,
                 suffix: long.into(),
                 suffix_len: long.len(),
             },]
diff --git a/src/format.rs b/src/format.rs
index bbc6e9f5..ab0e856f 100644
--- a/src/format.rs
+++ b/src/format.rs
@@ -55,6 +55,7 @@ pub struct FormatStringPlaceholderData<'a> {
     pub placeholder: Option<Placeholder<'a>>,
     pub alignment_spec: Option<Align>,
     pub width: Option<usize>,
+    pub precision: Option<usize>,
     pub suffix: SmolStr,
     pub suffix_len: usize,
 }
@@ -90,6 +91,9 @@ pub fn make_placeholder_regex(labels: &[&str]) -> Regex {
         ([<^>])     #         3: Alignment spec
       )?            #
       (\d+)         #     4: Width
+      (?:           #     Start optional precision (non-capturing)
+        \.(\d+)     #         5: Precision
+      )?            #
     )?              #
     \}}
     ",
@@ -134,6 +138,11 @@ pub fn parse_line_number_format<'a>(
                     .parse()
                     .unwrap_or_else(|_| panic!("Invalid width in format string: {}", format_string))
             }),
+            precision: captures.get(5).map(|m| {
+                m.as_str().parse().unwrap_or_else(|_| {
+                    panic!("Invalid precision in format string: {}", format_string)
+                })
+            }),
             suffix,
             suffix_len,
         });
@@ -156,10 +165,42 @@ pub fn parse_line_number_format<'a>(
     format_data
 }
 
-pub fn pad(s: &str, width: usize, alignment: &Align) -> String {
-    match alignment {
-        Align::Left => format!("{0:<1$}", s, width),
-        Align::Center => format!("{0:^1$}", s, width),
-        Align::Right => format!("{0:>1$}", s, width),
+// Note that in this case of a string `s`, `precision` means "max width".
+// See https://doc.rust-lang.org/std/fmt/index.html
+pub fn pad(s: &str, width: usize, alignment: &Align, precision: Option<usize>) -> String {
+    match precision {
+        None => match alignment {
+            Align::Left => format!("{0:<1$}", s, width),
+            Align::Center => format!("{0:^1$}", s, width),
+            Align::Right => format!("{0:>1$}", s, width),
+        },
+        Some(precision) => match alignment {
+            Align::Left => format!("{0:<1$.2$}", s, width, precision),
+            Align::Center => format!("{0:^1$.2$}", s, width, precision),
+            Align::Right => format!("{0:>1$.2$}", s, width, precision),
+        },
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_placeholder_regex() {
+        let regex = make_placeholder_regex(&["placeholder"]);
+        assert_eq!(
+            parse_line_number_format("prefix {placeholder:<15.14} suffix", &regex, false),
+            vec![FormatStringPlaceholderData {
+                prefix: "prefix ".into(),
+                placeholder: Some(Placeholder::Str("placeholder")),
+                alignment_spec: Some(Align::Left),
+                width: Some(15),
+                precision: Some(14),
+                suffix: " suffix".into(),
+                prefix_len: 7,
+                suffix_len: 7,
+            }]
+        );
     }
 }