Improve macro-stats printing.

By allowing long names to overlap with the "Uses" field when it has
spare space. This avoids unnecessary line breaks in the output.

Author: nnethercote

compiler/rustc_interface/src/passes.rs

@@ -341,20 +341,30 @@ fn print_macro_stats(ecx: &ExtCtxt<'_>) {
     }
     for (bytes, lines, uses, name, kind) in macro_stats {
         let mut name = ExpnKind::Macro(kind, *name).descr();
+        let uses_with_underscores = thousands::usize_with_underscores(uses);
         let avg_lines = lines as f64 / uses as f64;
         let avg_bytes = bytes as f64 / uses as f64;
-        if name.len() >= name_w {
-            // If the name is long, print it on a line by itself, then
-            // set the name to empty and print things normally, to show the
-            // stats on the next line.
+
+        // Ensure the "Macro Name" and "Uses" columns are as compact as possible.
+        let mut uses_w = uses_w;
+        if name.len() + uses_with_underscores.len() >= name_w + uses_w {
+            // The name would abut or overlap the uses value. Print the name
+            // on a line by itself, then set the name to empty and print things
+            // normally, to show the stats on the next line.
             _ = writeln!(s, "{prefix} {:<name_w$}", name);
             name = String::new();
-        }
+        } else if name.len() >= name_w {
+            // The name won't abut or overlap with the uses value, but it does
+            // overlap with the empty part of the uses column. Shrink the width
+            // of the uses column to account for the excess name length.
+            uses_w = uses_with_underscores.len() + 1
+        };
+
         _ = writeln!(
             s,
             "{prefix} {:<name_w$}{:>uses_w$}{:>lines_w$}{:>avg_lines_w$}{:>bytes_w$}{:>avg_bytes_w$}",
             name,
-            thousands::usize_with_underscores(uses),
+            uses_with_underscores,
             thousands::usize_with_underscores(lines),
             thousands::f64p1_with_underscores(avg_lines),
             thousands::usize_with_underscores(bytes),

tests/ui/stats/macro-stats.stderr

@@ -22,7 +22,6 @@ macro-stats trait_tys!                            1          2        2.0
 macro-stats n99!                                  2          2        1.0          4        2.0
 macro-stats none!                                 1          1        1.0          4        4.0
 macro-stats u32!                                  1          1        1.0          3        3.0
-macro-stats long_name_that_fits_on_a_single_line!
-macro-stats                                       1          1        1.0          0        0.0
+macro-stats long_name_that_fits_on_a_single_line! 1          1        1.0          0        0.0
 macro-stats #[test]                               1          1        1.0          0        0.0
 macro-stats ===================================================================================