internal/shader: bug fix: spaces around a compiler directive should be allowed

Closes #2771

internal/shader/shader.go

@@ -222,7 +222,9 @@ func ParseCompilerDirectives(src []byte) (shaderir.Unit, error) {
 	// TODO: Change the unit to pixels in v3 (#2645).
 	unit := shaderir.Texels
 
-	reUnit := regexp.MustCompile(`^//kage:unit\s+(.+)$`)
+	// Go's whitespace is U+0020 (SP), U+0009 (\t), U+000d (\r), and U+000A (\n).
+	// See https://go.dev/ref/spec#Tokens
+	reUnit := regexp.MustCompile(`^[ \t\r\n]*//kage:unit\s+([^ \t\r\n]+)[ \t\r\n]*$`)
 	var unitParsed bool
 
 	buf := bytes.NewBuffer(src)

internal/shader/syntax_test.go

@@ -3311,6 +3311,16 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 }`,
 			err: true,
 		},
+		{
+			src: "\t    " + `//kage:unit pixels` + "    \t\r" + `
+package main
+
+func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
+	return position
+}`,
+			unit: shaderir.Pixels,
+			err:  false,
+		},
 	}
 	for _, c := range cases {
 		ir, err := compileToIR([]byte(c.src))