fmt::Formatter::pad: don't call chars().count() more than one time

library/core/src/fmt/mod.rs

@@ -402,7 +402,7 @@ impl<'a> Arguments<'a> {
 
         if self.args.is_empty() {
             pieces_length
-        } else if self.pieces[0] == "" && pieces_length < 16 {
+        } else if !self.pieces.is_empty() && self.pieces[0].is_empty() && pieces_length < 16 {
             // If the format string starts with an argument,
             // don't preallocate anything, unless length
             // of pieces is significant.
@@ -1163,7 +1163,7 @@ pub fn write(output: &mut dyn Write, args: Arguments<'_>) -> Result {
                 }
                 // SAFETY: arg and args.args come from the same Arguments,
                 // which guarantees the indexes are always within bounds.
-                unsafe { run(&mut formatter, arg, &args.args) }?;
+                unsafe { run(&mut formatter, arg, args.args) }?;
                 idx += 1;
             }
         }
@@ -1409,7 +1409,7 @@ impl<'a> Formatter<'a> {
                 // we know that it can't panic. Use `get` + `unwrap_or` to avoid
                 // `unsafe` and otherwise don't emit any panic-related code
                 // here.
-                s.get(..i).unwrap_or(&s)
+                s.get(..i).unwrap_or(s)
             } else {
                 &s
             }
@@ -1421,16 +1421,21 @@ impl<'a> Formatter<'a> {
             // If we're under the maximum length, and there's no minimum length
             // requirements, then we can just emit the string
             None => self.buf.write_str(s),
-            // If we're under the maximum width, check if we're over the minimum
-            // width, if so it's as easy as just emitting the string.
-            Some(width) if s.chars().count() >= width => self.buf.write_str(s),
-            // If we're under both the maximum and the minimum width, then fill
-            // up the minimum width with the specified string + some alignment.
             Some(width) => {
-                let align = rt::v1::Alignment::Left;
-                let post_padding = self.padding(width - s.chars().count(), align)?;
-                self.buf.write_str(s)?;
-                post_padding.write(self.buf)
+                let chars_count = s.chars().count();
+                // If we're under the maximum width, check if we're over the minimum
+                // width, if so it's as easy as just emitting the string.
+                if chars_count >= width {
+                    self.buf.write_str(s)
+                }
+                // If we're under both the maximum and the minimum width, then fill
+                // up the minimum width with the specified string + some alignment.
+                else {
+                    let align = rt::v1::Alignment::Left;
+                    let post_padding = self.padding(width - chars_count, align)?;
+                    self.buf.write_str(s)?;
+                    post_padding.write(self.buf)
+                }
             }
         }
     }