v4.0.0-rc1: `measureText` collapses trailing/isolated whitespace to zero width (regression from v3, diverges from browsers)

[lvcabral]

In canvas@4.0.0-rc1 ( PR #2602 ), ctx.measureText() does not count the advance of trailing whitespace. In consequence:

• A whitespace-only string (" ", "\t") measures as width: 0.
• " " (two spaces) measures as one space's width.
• "word " measures barely wider than "word" (the trailing space advance is mostly dropped).
• A leading space is fine: " word" correctly measures as space + word.

v3.x counted all whitespace advances, matching browser behavior (Chrome/Firefox/Safari all return the real space advance for measureText(" "), per the spec's definition of text advance width — the sum of glyph advances, with no trailing-whitespace trimming).

This breaks a common layout technique: tokenizing a string into words and spaces, measuring each token separately, and advancing a cursor by each token's width (e.g. word-wrap with per-word styling, like rich-text/multi-font labels). On v4 every isolated space token measures 0, so all words render butted together — while the same code renders correctly in browsers and on canvas v3.

Steps to reproduce

const { createCanvas } = require("canvas");
const ctx = createCanvas(100, 100).getContext("2d");
ctx.font = "36px sans-serif";

console.log(ctx.measureText(" ").width);   // v4: 0        v3: ~10
console.log(ctx.measureText("  ").width);  // v4: ~10 (!)  v3: ~20
console.log(ctx.measureText("\t").width);  // v4: 0        v3: ~80

Measured comparison (same machine, 36px sans-serif)

Input	v3.2.3	v4.0.0-rc1	Browser-consistent?
" "	10.00	0	❌
" "	20.00	10.01	❌
"\t"	80.02	0	❌
"word"	78.03	75.67	— (font engine changed, fine)
"word "	88.03	78.01	❌ (space adds only ~2.3)
" word"	88.03	85.68	✅ (leading space kept)
"a b" − "ab"	10.00	10.01	✅ (interior space kept)

The pattern: the advance of whitespace at the end of the measured string is dropped.

Full TextMetrics for " " on v4 — width and all actualBoundingBox* fields are 0, only the em-height fields are populated:

{
  "width": 0,
  "actualBoundingBoxLeft": 0,
  "actualBoundingBoxRight": 0,
  "actualBoundingBoxAscent": 0,
  "actualBoundingBoxDescent": 0,
  "emHeightAscent": 27.72,
  "emHeightDescent": -8.28,
  "alphabeticBaseline": 0
}

Environment

• canvas: 4.0.0-rc1 (prebuilt binary from npm, canvas-darwin-arm64)
• Node.js: v22.22.2
• OS: macOS 15.7.7 (Darwin 24.6.0), Apple Silicon (arm64)
• Baseline: canvas 3.2.3 on the same machine

Expected behavior

Match v3 / the HTML spec / browsers: measureText returns the full advance width including trailing whitespace, so:

• measureText(" ").width > 0
• measureText("word ") ≈ measureText("word") + measureText(" ")

Possibly related

I also reported the empty-string SIGTRAP crash (measureText("") aborts the process) — both look like the new text layout path treating degenerate/whitespace paragraphs specially, so they may share a fix.

[chearon]

Fixed in rc2, thanks.