Commit `0e719f049c`

0e719f049cb904a5aa8409fe3a260cab77fabd62

parent: b3b4b490f0

Verified · cmc ci/build: success

cmc <hello@cleberg.net> · 2026-08-26T23:06:41Z

web: pick syntax palettes on measured contrast

friendly, chroma's default, put 61 token/ground pairs under 4.5:1 against
the grounds code actually sits on here — page, code block, and the two
diff tints. Comments came out at 2.5:1. Light uses xcode now, which puts
one pair under, overridden to clear it.

github-dark's line numbers were 4.31:1 on the page; lifted to the grey
its comments use.

TestSyntaxPaletteContrast holds both palettes to the floor so a future
style swap has to answer for it.

internal/httpd/diff.go +1 −1

		@@ -227,7 +227,7 @@ func highlightLines(lexer chroma.Lexer, src string) []template.HTML {
227	227	return nil
228	228	}
229	229	var buf bytes.Buffer
230		if err := diffFormatter.Format(&buf, styles.Get("friendly"), it); err != nil {
	230	if err := diffFormatter.Format(&buf, styles.Get(lightStyle), it); err != nil {
231	231	return nil
232	232	}
233	233	body := buf.String()

internal/httpd/palette_test.go added +96

		@@ -0,0 +1,96 @@
	1	package httpd
	2
	3	import (
	4	"math"
	5	"testing"
	6
	7	"github.com/alecthomas/chroma/v2"
	8	"github.com/alecthomas/chroma/v2/styles"
	9	)
	10
	11	func channel(v float64) float64 {
	12	if v <= 0.03928 {
	13	return v / 12.92
	14	}
	15	return math.Pow((v+0.055)/1.055, 2.4)
	16	}
	17
	18	func luminance(c chroma.Colour) float64 {
	19	return 0.2126*channel(float64(c.Red())/255) +
	20	0.7152*channel(float64(c.Green())/255) +
	21	0.0722*channel(float64(c.Blue())/255)
	22	}
	23
	24	func contrast(a, b chroma.Colour) float64 {
	25	hi, lo := luminance(a), luminance(b)
	26	if hi < lo {
	27	hi, lo = lo, hi
	28	}
	29	return (hi + 0.05) / (lo + 0.05)
	30	}
	31
	32	// TestSyntaxPaletteContrast holds both palettes to WCAG AA for body text
	33	// against every ground code sits on here: the page, a code block, and the
	34	// two diff tints. The chroma default (friendly) put 61 token/ground pairs
	35	// under the floor, which is why the styles are chosen rather than assumed.
	36	//
	37	// Two tokens are exempted because the stylesheet overrides them after
	38	// writing the palette, which this test cannot see: NameAttribute in light
	39	// (#6f5a21) and the line-number tokens in dark (#8b949e).
	40	func TestSyntaxPaletteContrast(t *testing.T) {
	41	const floor = 4.5
	42	// chroma's own line-number gutter renders on blob pages only — the diff
	43	// supplies its own gutter — so those tokens are checked against the page
	44	// and code grounds, never against a diff tint.
	45	gutterOnly := map[chroma.TokenType]bool{
	46	chroma.LineNumbers: true, chroma.LineNumbersTable: true,
	47	chroma.LineHighlight: true, chroma.LineTable: true, chroma.LineTableTD: true,
	48	}
	49	cases := []struct {
	50	style string
	51	grounds map[string]chroma.Colour
	52	exempt map[chroma.TokenType]bool
	53	}{
	54	{lightStyle, map[string]chroma.Colour{
	55	"page": chroma.NewColour(0xff, 0xff, 0xff),
	56	"code": chroma.NewColour(0xf5, 0xf5, 0xf5),
	57	"add": chroma.NewColour(0xe4, 0xf6, 0xea),
	58	"del": chroma.NewColour(0xfd, 0xea, 0xea),
	59	}, map[chroma.TokenType]bool{chroma.NameAttribute: true}},
	60	{darkStyle, map[string]chroma.Colour{
	61	"page": chroma.NewColour(0x0a, 0x0a, 0x0a),
	62	"code": chroma.NewColour(0x05, 0x05, 0x05),
	63	"add": chroma.NewColour(0x0d, 0x2a, 0x18),
	64	"del": chroma.NewColour(0x2c, 0x11, 0x13),
	65	}, map[chroma.TokenType]bool{
	66	chroma.LineNumbers: true, chroma.LineNumbersTable: true,
	67	}},
	68	}
	69
	70	for _, tc := range cases {
	71	st := styles.Get(tc.style)
	72	if st == nil \|\| st.Name != tc.style {
	73	t.Fatalf("chroma style %q is not available", tc.style)
	74	}
	75	for _, tt := range st.Types() {
	76	// Whitespace markers are meant to be near-invisible, and the
	77	// background entry is a ground, not text.
	78	if tt == chroma.TextWhitespace \|\| tt == chroma.Background \|\| tc.exempt[tt] {
	79	continue
	80	}
	81	e := st.Get(tt)
	82	if !e.Colour.IsSet() {
	83	continue
	84	}
	85	for name, ground := range tc.grounds {
	86	if gutterOnly[tt] && (name == "add" \|\| name == "del") {
	87	continue
	88	}
	89	if got := contrast(e.Colour, ground); got < floor {
	90	t.Errorf("%s: %s (%s) on %s is %.2f:1, want >= %.1f",
	91	tc.style, tt, e.Colour, name, got, floor)
	92	}
	93	}
	94	}
	95	}
	96	}

internal/httpd/web.go +19 −4

		@@ -823,7 +823,7 @@ func highlight(filePath string, data []byte) template.HTML {
823	823	return template.HTML("<pre>" + template.HTMLEscapeString(string(data)) + "</pre>")
824	824	}
825	825	var buf bytes.Buffer
826		if err := chromaFormatter.Format(&buf, styles.Get("friendly"), iterator); err != nil {
	826	if err := chromaFormatter.Format(&buf, styles.Get(lightStyle), iterator); err != nil {
827	827	return template.HTML("<pre>" + template.HTMLEscapeString(string(data)) + "</pre>")
828	828	}
829	829	return template.HTML(buf.String())
		@@ -835,12 +835,27 @@ func highlight(filePath string, data []byte) template.HTML {
835	835	// light-theme colour on a black ground — NameAttribute landed at 2.97:1.
836	836	// Scoped, an unnamed token inherits the wrapper's colour instead, which is
837	837	// readable in both. The site's --code-bg stays the background either way.
	838	// lightStyle and darkStyle are chosen on measured contrast against the
	839	// grounds code actually sits on here — page, code block, and the diff
	840	// tints. friendly, the chroma default, put 61 token/ground pairs under
	841	// 4.5:1; xcode puts one.
	842	const (
	843	lightStyle = "xcode"
	844	darkStyle = "github-dark"
	845	)
	846
838	847	var chromaCSS = func() []byte {
839	848	var buf bytes.Buffer
840	849	buf.WriteString("@media (prefers-color-scheme: light) {\n")
841		chromaFormatter.WriteCSS(&buf, styles.Get("friendly"))
	850	chromaFormatter.WriteCSS(&buf, styles.Get(lightStyle))
	851	// xcode's NameAttribute is its one token under 4.5:1 against the diff
	852	// tints (4.51 on additions, 4.38 on deletions); darkened it clears both.
	853	buf.WriteString(".chroma .na { color: #6f5a21 }\n")
842	854	buf.WriteString("}\n@media (prefers-color-scheme: dark) {\n")
843		chromaFormatter.WriteCSS(&buf, styles.Get("github-dark"))
	855	chromaFormatter.WriteCSS(&buf, styles.Get(darkStyle))
	856	// github-dark's line numbers are #6e7681, 4.31:1 on the page; lifted to
	857	// the same grey its comments use, which clears the floor.
	858	buf.WriteString(".chroma .lnt, .chroma .ln { color: #8b949e }\n")
844	859	buf.WriteString("}\n.chroma, .bg { background: transparent !important; }\n")
845	860	return buf.Bytes()
846	861	}()
		@@ -923,7 +938,7 @@ func fenceHighlight(source, lang string) string {
923	938	}
924	939	var buf bytes.Buffer
925	940	f := html.New(html.WithClasses(true))
926		if err := f.Format(&buf, styles.Get("friendly"), iterator); err != nil {
	941	if err := f.Format(&buf, styles.Get(lightStyle), iterator); err != nil {
927	942	return "<pre>" + template.HTMLEscapeString(source) + "</pre>"
928	943	}
929	944	return buf.String()

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