Format code size differences with grouping and unit display.

Author: detly

.github/workflows/check-binary-size.yml

@@ -112,19 +112,34 @@ jobs:
               return;
             }
 
+            const formatter = Intl.NumberFormat("en", {useGrouping: "always"});
+
+            const updated_str = formatter.format(updated);
+            const reference_str = formatter.format(reference);
+
             const diff = updated - reference;
-            const plus = diff > 0 ? "+" : "";
-            const diff_str = `${plus}${diff}B`;
+            const diff_pct = (updated / reference) - 1;
+
+            const diff_str = Intl.NumberFormat("en", {
+              useGrouping: "always",
+              sign: "exceptZero"
+            }).format(diff);
+
+            const diff_pct_str = Intl.NumberFormat("en", {
+              style: "percent",
+              useGrouping: "always",
+              sign: "exceptZero",
+              maximumFractionDigits: 2
+            }).format(diff_pct);
 
             if (diff !== 0) {
-              const percent = (((updated / reference) - 1) * 100).toFixed(2);
               // The body is created here and wrapped so "weirdly" to avoid whitespace at the start of the lines,
               // which is interpreted as a code block by Markdown.
               const body = `Below is the size of a hello-world Rust program linked with libstd with backtrace.
 
-            Original binary size: **${reference}B**
-            Updated binary size: **${updated}B**
-            Difference: **${diff_str}** (${percent}%)`;
+            Original binary size: **${reference_str} B**
+            Updated binary size: **${updated_str} B**
+            Difference: **${diff_str} B** (${diff_pct_str})`;
 
               github.rest.issues.createComment({
                 issue_number: context.issue.number,