update-built-tests.sh locally results in many differences

[foolip]

On a Linux machine (not macOS as in #23292) running ./update-built-tests.sh from a completely clean (git clean -fdx'd) repo results in a bunch of changes. git status shows:

HEAD detached at origin/master
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
	modified:   2dcontext/drawing-text-to-the-canvas/2d.text.draw.fill.basic.png
	modified:   2dcontext/drawing-text-to-the-canvas/2d.text.draw.fill.maxWidth.large.png
	modified:   2dcontext/drawing-text-to-the-canvas/2d.text.draw.fill.rtl.png
	modified:   2dcontext/drawing-text-to-the-canvas/2d.text.draw.stroke.basic.png
	modified:   offscreen-canvas/text/2d.text.draw.fill.basic.png
	modified:   offscreen-canvas/text/2d.text.draw.fill.maxWidth.large.png
	modified:   offscreen-canvas/text/2d.text.draw.fill.rtl.png
	modified:   offscreen-canvas/text/2d.text.draw.stroke.basic.png

Untracked files:
  (use "git add <file>..." to include in what will be committed)
	2dcontext/annotated-spec.html
	2dcontext/clear-100x50.png
	2dcontext/green-100x50.png
	generated-mime-types.json
	offscreen-canvas/green-100x50.png

no changes added to commit (use "git add" and/or "git commit -a")

The problems are:

• PNGs with differences
• generated-mime-types.json is written to the wrong location, should be mimesniff/mime-types/resources/generated-mime-types.json
• 2dcontext/annotated-spec.html is created. Is it needed for anything?

[foolip]

#23070 renamed some things so annotated-spec.html will be elsewhere now.

[stephenmcgruer]

This is what I see:

Untracked files:
  (use "git add <file>..." to include in what will be committed)

        generated-mime-types.json
        html/canvas/element/green-100x50.png
        html/canvas/offscreen/green-100x50.png

./tools/ci/ci_built_diff.sh returns clean, looks like it explicitly excludes some files:

    # Exclude tests that rely on font rendering
    excluded=(
        'html/canvas/element/drawing-text-to-the-canvas/2d.text.draw.fill.basic.png'
        'html/canvas/element/drawing-text-to-the-canvas/2d.text.draw.fill.maxWidth.large.png'
        'html/canvas/element/drawing-text-to-the-canvas/2d.text.draw.fill.rtl.png'
        'html/canvas/element/drawing-text-to-the-canvas/2d.text.draw.stroke.basic.png'
        'html/canvas/offscreen/text/2d.text.draw.fill.basic.png'
        'html/canvas/offscreen/text/2d.text.draw.fill.maxWidth.large.png'
        'html/canvas/offscreen/text/2d.text.draw.fill.rtl.png'
        'html/canvas/offscreen/text/2d.text.draw.stroke.basic.png'
    )

And indeed they appear to be ignored:

$ git ls-files -v|grep '^h'
h html/canvas/element/drawing-text-to-the-canvas/2d.text.draw.fill.basic.png
h html/canvas/element/drawing-text-to-the-canvas/2d.text.draw.fill.maxWidth.large.png
h html/canvas/element/drawing-text-to-the-canvas/2d.text.draw.fill.rtl.png
h html/canvas/element/drawing-text-to-the-canvas/2d.text.draw.stroke.basic.png
h html/canvas/offscreen/text/2d.text.draw.fill.basic.png
h html/canvas/offscreen/text/2d.text.draw.fill.maxWidth.large.png
h html/canvas/offscreen/text/2d.text.draw.fill.rtl.png
h html/canvas/offscreen/text/2d.text.draw.stroke.basic.png

This seems to be a deliberate ignoring, so cc @jgraham and @Hexcles who have modified the diff-checker tool and may have some background, but otherwise marking backlog.

[Hexcles]

PNGs with differences
This is what @stephenmcgruer pointed to. Essentially, these automatically generated assets include text which vary subtly depending on system fonts and rendering settings, so they are intentionally ignored.

Perhaps we could expand "# Exclude tests that rely on font rendering" to include more explanation, but I'm not sure what.

Meanwhile, we should ask someone more familiar with these canvas/2dcontext tests regarding the other two cases. Also, it's probably up to them if they want to invest making the asset generation platform-independent.