util: improve inspect() compact number mode

This fixes a proportion calculation for lots of short array entries
with at least one bigger one that alone makes up for more than one
fifth of all other entries together.

PR-URL: #26984
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

lib/internal/util/inspect.js

@@ -878,26 +878,27 @@ function groupArrayElements(ctx, output) {
   let totalLength = 0;
   let maxLength = 0;
   let i = 0;
+  const separatorSpace = 2; // Add 1 for the space and 1 for the separator.
   const dataLen = new Array(output.length);
   // Calculate the total length of all output entries and the individual max
   // entries length of all output entries. We have to remove colors first,
   // otherwise the length would not be calculated properly.
   for (; i < output.length; i++) {
     const len = ctx.colors ? removeColors(output[i]).length : output[i].length;
     dataLen[i] = len;
-    totalLength += len;
+    totalLength += len + separatorSpace;
     if (maxLength < len)
       maxLength = len;
   }
   // Add two to `maxLength` as we add a single whitespace character plus a comma
   // in-between two entries.
-  const actualMax = maxLength + 2;
+  const actualMax = maxLength + separatorSpace;
   // Check if at least three entries fit next to each other and prevent grouping
   // of arrays that contains entries of very different length (i.e., if a single
   // entry is longer than 1/5 of all other entries combined). Otherwise the
   // space in-between small entries would be enormous.
   if (actualMax * 3 + ctx.indentationLvl < ctx.breakLength &&
-      (totalLength / maxLength > 5 || maxLength <= 6)) {
+      (totalLength / actualMax > 5 || maxLength <= 6)) {
 
     const approxCharHeights = 2.5;
     const bias = 1;

test/parallel/test-util-inspect.js

@@ -2121,6 +2121,30 @@ assert.strictEqual(
 
   assert.strictEqual(out, expected);
 
+  obj = [
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    1, 1, 1, 1, 1, 1, 123456789
+  ];
+
+  out = util.inspect(obj, { compact: 3 });
+
+  expected = [
+    '[',
+    '  1,         1,         1,',
+    '  1,         1,         1,',
+    '  1,         1,         1,',
+    '  1,         1,         1,',
+    '  1,         1,         1,',
+    '  1,         1,         1,',
+    '  1,         1,         1,',
+    '  1,         1,         1,',
+    '  1,         1, 123456789',
+    ']'
+  ].join('\n');
+
+  assert.strictEqual(out, expected);
+
   // Verify that array grouping and line consolidation does not happen together.
   obj = {
     a: {