Add some more KaTeX options

And fix the options handling.

Closes #12745
Fixes #12746

tpl/transform/transform.go

@@ -211,13 +211,14 @@ func (ns *Namespace) ToMath(ctx context.Context, args ...any) (template.HTML, er
 	katexInput := warpc.KatexInput{
 		Expression: expression,
 		Options: warpc.KatexOptions{
-			Output:       "mathml",
-			ThrowOnError: false,
+			Output:           "mathml",
+			MinRuleThickness: 0.04,
+			ErrorColor:       "#cc0000",
 		},
 	}
 
 	if len(args) > 1 {
-		if err := mapstructure.WeakDecode(args[1], &katexInput); err != nil {
+		if err := mapstructure.WeakDecode(args[1], &katexInput.Options); err != nil {
 			return "", err
 		}
 	}

tpl/transform/transform_integration_test.go

@@ -149,3 +149,24 @@ disableKinds = ['page','rss','section','sitemap','taxonomy','term']
 <span class="katex"><math
 	`)
 }
+
+func TestToMathMacros(t *testing.T) {
+	t.Parallel()
+
+	files := `
+-- hugo.toml --
+disableKinds = ['page','rss','section','sitemap','taxonomy','term']
+-- layouts/index.html --
+{{ $macros := dict 
+    "\\addBar" "\\bar{#1}"
+	"\\bold" "\\mathbf{#1}"
+}}
+{{ $opts := dict "macros" $macros }}
+{{ transform.ToMath "\\addBar{y} + \\bold{H}" $opts }}
+  `
+	b := hugolib.Test(t, files)
+
+	b.AssertFileContent("public/index.html", `
+<mi>y</mi>
+	`)
+}