Remove unneeded whitespace generation and use CSS instead instead to align line numbers to the right

src/librustdoc/html/sources.rs

@@ -272,22 +272,16 @@ fn emit_source(
 ) {
     let lines = s.lines().count();
     let mut line_numbers = Buffer::empty_from(buf);
-    let mut cols = 0;
-    let mut tmp = lines;
-    while tmp > 0 {
-        cols += 1;
-        tmp /= 10;
-    }
     line_numbers.write_str("<pre class=\"line-numbers\">");
     match source_context {
         SourceContext::Standalone => {
             for line in 1..=lines {
-                writeln!(line_numbers, "<span id=\"{0}\">{0:1$}</span>", line, cols)
+                writeln!(line_numbers, "<span id=\"{0}\">{0}</span>", line)
             }
         }
         SourceContext::Embedded { offset } => {
             for line in 1..=lines {
-                writeln!(line_numbers, "<span>{0:1$}</span>", line + offset, cols)
+                writeln!(line_numbers, "<span>{0}</span>", line + offset)
             }
         }
     }

src/librustdoc/html/static/css/rustdoc.css

@@ -541,6 +541,9 @@ h2.location a {
 	text-decoration: underline;
 }
 
+.line-numbers {
+	text-align: right;
+}
 .rustdoc:not(.source) .example-wrap > pre:not(.line-number) {
 	width: 100%;
 	overflow-x: auto;