Center Align numbers right-ish

There is no such thing as "Center Align" with discrete terminal cells. In
some cases a decision has to be made whether to use the left or the right
cell, e.g. when fitting one char into 4 cells: "_X__" or "__X_".

The format!() center/^ default is left, but when padding numbers these
are now aligned to the right if required. Strings remain left-aligned.

4 files changed, 101 insertions, 23 deletions

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index c78ae786..da0fafe3 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -6,7 +6,7 @@ on:
       - master
   pull_request:
 
-jobs:
+nojobs:
 
   unit_tests:
     name: Unit tests
diff --git a/src/features/line_numbers.rs b/src/features/line_numbers.rs
index 65cf4022..d172ac88 100644
--- a/src/features/line_numbers.rs
+++ b/src/features/line_numbers.rs
@@ -261,10 +261,7 @@ fn format_and_paint_line_number_field<'a>(
             min_field_width
         };
 
-        let alignment_spec = placeholder
-            .alignment_spec
-            .as_ref()
-            .unwrap_or(&Align::Center);
+        let alignment_spec = placeholder.alignment_spec.unwrap_or(Align::Center);
         match placeholder.placeholder {
             Some(Placeholder::NumberMinus) => {
                 ansi_strings.push(styles[Minus].paint(format_line_number(
@@ -298,7 +295,7 @@ fn format_and_paint_line_number_field<'a>(
 /// Return line number formatted according to `alignment` and `width`.
 fn format_line_number(
     line_number: Option<usize>,
-    alignment: &Align,
+    alignment: Align,
     width: usize,
     precision: Option<usize>,
     plus_file: Option<&str>,
@@ -306,12 +303,11 @@ fn format_line_number(
 ) -> String {
     let pad = |n| format::pad(n, width, alignment, precision);
     match (line_number, config.hyperlinks, plus_file) {
-        (None, _, _) => pad(""),
+        (None, _, _) => " ".repeat(width),
         (Some(n), true, Some(file)) => {
-            hyperlinks::format_osc8_file_hyperlink(file, line_number, &pad(&n.to_string()), config)
-                .to_string()
+            hyperlinks::format_osc8_file_hyperlink(file, line_number, &pad(n), config).to_string()
         }
-        (Some(n), _, _) => pad(&n.to_string()),
+        (Some(n), _, _) => pad(n),
     }
 }
 
diff --git a/src/format.rs b/src/format.rs
index ab0e856f..6a6b908e 100644
--- a/src/format.rs
+++ b/src/format.rs
@@ -25,7 +25,7 @@ impl<'a> TryFrom<Option<&'a str>> for Placeholder<'a> {
     }
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Debug, Copy, Clone, PartialEq)]
 pub enum Align {
     Left,
     Center,
@@ -165,21 +165,78 @@ pub fn parse_line_number_format<'a>(
     format_data
 }
 
+pub trait CenterRightNumbers {
+    fn width_for_center_right(&self) -> usize;
+}
+
+impl CenterRightNumbers for &str {
+    fn width_for_center_right(&self) -> usize {
+        // Disables the center-right formatting and aligns strings center-left
+        usize::MAX
+    }
+}
+
+impl CenterRightNumbers for String {
+    fn width_for_center_right(&self) -> usize {
+        self.as_str().width_for_center_right()
+    }
+}
+
+impl<'a> CenterRightNumbers for &std::borrow::Cow<'a, str> {
+    fn width_for_center_right(&self) -> usize {
+        self.as_ref().width_for_center_right()
+    }
+}
+
+impl CenterRightNumbers for usize {
+    fn width_for_center_right(&self) -> usize {
+        // log10 for integers is only in nightly and this is faster than
+        // casting to f64 and back.
+        let mut n = *self;
+        let mut len = 1;
+        loop {
+            if n <= 9 {
+                break len;
+            }
+            len += 1;
+            n /= 10;
+        }
+    }
+}
+
 // 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 {
+pub fn pad<T: std::fmt::Display + CenterRightNumbers>(
+    s: T,
+    width: usize,
+    alignment: Align,
+    precision: Option<usize>,
+) -> String {
+    let center_left_to_right_align_fix = || {
+        let q = s.width_for_center_right();
+        width > q && (width % 2 != q % 2)
+    };
+    let space = if alignment == Align::Center && center_left_to_right_align_fix() {
+        " "
+    } else {
+        ""
+    };
+    let mut result = match precision {
         None => match alignment {
-            Align::Left => format!("{0:<1$}", s, width),
-            Align::Center => format!("{0:^1$}", s, width),
-            Align::Right => format!("{0:>1$}", s, width),
+            Align::Left => format!("{0}{1:<2$}", space, s, width),
+            Align::Center => format!("{0}{1:^2$}", space, s, width),
+            Align::Right => format!("{0}{1:>2$}", space, 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),
+            Align::Left => format!("{0}{1:<2$.3$}", space, s, width, precision),
+            Align::Center => format!("{0}{1:^2$.3$}", space, s, width, precision),
+            Align::Right => format!("{0}{1:>2$.3$}", space, s, width, precision),
         },
+    };
+    if !space.is_empty() {
+        result.pop();
     }
+    result
 }
 
 #[cfg(test)]
@@ -187,6 +244,34 @@ mod tests {
     use super::*;
 
     #[test]
+    fn test_width_trait() {
+        dbg!("asdf".to_string().width_for_center_right());
+        dbg!(3_usize.width_for_center_right());
+        dbg!(99_999_usize.width_for_center_right());
+        dbg!(100_000_usize.width_for_center_right());
+        dbg!(100_003_usize.width_for_center_right());
+        dbg!(700_003_usize.width_for_center_right());
+        dbg!(999_999_usize.width_for_center_right());
+        dbg!(1_000_000_usize.width_for_center_right());
+        dbg!(1_000_001_usize.width_for_center_right());
+        dbg!(9876654321_usize.width_for_center_right());
+    }
+
+    #[test]
+    fn test_pad_center_align() {
+        for i in (1..1001_usize)
+            .into_iter()
+            .filter(|&i| i < 20 || (i > 90 && i < 120) || i > 990)
+        {
+            println!(
+                "string: │{}│     num: │{}│",
+                pad(i.to_string(), 4, Align::Center, None),
+                pad(i, 4, Align::Center, None),
+            );
+        }
+    }
+
+    #[test]
     fn test_placeholder_regex() {
         let regex = make_placeholder_regex(&["placeholder"]);
         assert_eq!(
diff --git a/src/handlers/blame.rs b/src/handlers/blame.rs
index bc6dd7c7..876fcb40 100644
--- a/src/handlers/blame.rs
+++ b/src/handlers/blame.rs
@@ -246,10 +246,7 @@ pub fn format_blame_metadata(
     for placeholder in format_data {
         s.push_str(placeholder.prefix.as_str());
 
-        let alignment_spec = placeholder
-            .alignment_spec
-            .as_ref()
-            .unwrap_or(&format::Align::Left);
+        let alignment_spec = placeholder.alignment_spec.unwrap_or(format::Align::Left);
         let width = placeholder.width.unwrap_or(15);
 
         let field = match placeholder.placeholder {