fix #1397: support "s" in css attribute selectors

CHANGELOG.md

@@ -38,6 +38,10 @@
 
     The `translate3d` to `translateZ` conversion was contributed by [@steambap](https://github.com/steambap).
 
+* Support for the case-sensitive flag in CSS attribute selectors ([#1397](https://github.com/evanw/esbuild/issues/1397))
+
+    You can now use the case-sensitive CSS attribute selector flag `s` such as in `[type="a" s] { list-style: lower-alpha; }`. Previously doing this caused a warning about unrecognized syntax.
+
 ## 0.12.9
 
 * Allow `this` with `--define` ([#1361](https://github.com/evanw/esbuild/issues/1361))

internal/css_parser/css_parser_selector.go

@@ -249,7 +249,7 @@ func (p *parser) parseAttributeSelector() (attr css_ast.SSAttribute, ok bool) {
 		p.eat(css_lexer.TWhitespace)
 		if p.peek(css_lexer.TIdent) {
 			if modifier := p.decoded(); len(modifier) == 1 {
-				if c := modifier[0]; c == 'i' || c == 'I' {
+				if c := modifier[0]; c == 'i' || c == 'I' || c == 's' || c == 'S' {
 					attr.MatcherModifier = c
 					p.advance()
 				}

internal/css_parser/css_parser_test.go

@@ -614,8 +614,12 @@ func TestSelector(t *testing.T) {
 
 	expectPrinted(t, "[b = \"c\" i] {}", "[b=c i] {\n}\n")
 	expectPrinted(t, "[b = \"c\" I] {}", "[b=c I] {\n}\n")
+	expectPrinted(t, "[b = \"c\" s] {}", "[b=c s] {\n}\n")
+	expectPrinted(t, "[b = \"c\" S] {}", "[b=c S] {\n}\n")
 	expectParseError(t, "[b i] {}", "<stdin>: warning: Expected \"]\" but found \"i\"\n<stdin>: warning: Unexpected \"]\"\n")
 	expectParseError(t, "[b I] {}", "<stdin>: warning: Expected \"]\" but found \"I\"\n<stdin>: warning: Unexpected \"]\"\n")
+	expectParseError(t, "[b s] {}", "<stdin>: warning: Expected \"]\" but found \"s\"\n<stdin>: warning: Unexpected \"]\"\n")
+	expectParseError(t, "[b S] {}", "<stdin>: warning: Expected \"]\" but found \"S\"\n<stdin>: warning: Unexpected \"]\"\n")
 
 	expectPrinted(t, "|b {}", "|b {\n}\n")
 	expectPrinted(t, "|* {}", "|* {\n}\n")