fix: parse CSS custom properties

This change only fixes the `CssScanner` to parse CSS custom properties
as IDENT tokens.

Additional work may be needed to actually make the built-in CSS Grammar
aware of custom properties, but at this time this is not needed to
prevent EPUBCheck from reporting custom properties as errors.

Fix #790

src/main/java/org/idpf/epubcheck/util/css/CssScanner.java

@@ -134,9 +134,10 @@ && matchesOrEOF(reader.at(2), URANGESTART))
  {
  _urange();
  }
- else if (NMSTART.matches(cur) || cur == '-'
- && matches(next, NMSTART) || escapes.get(0).isPresent()
- || (cur == '-' && escapes.get(1).isPresent()))
+ else if (NMSTART.matches(cur) 
+ || cur == '-' && 
+ (matches(next, NMSTART) || reader.peek() == '-' || escapes.get(1).isPresent())
+ || escapes.get(0).isPresent())
  {
  _ident();
  if (reader.peek() == '(')
@@ -406,7 +407,7 @@ private void _atkeyword() throws
  }
 
  /**
- * IDENT [-]?{nmstart}{nmchar}*
+ * IDENT ([-]?{nmstart}|[--]){nmchar}*
  */
  private void _ident() throws
  IOException,

src/test/java/org/idpf/epubcheck/util/css/CssParserTest.java

@@ -171,6 +171,13 @@ public void testParser014() throws Exception {
  assertTrue(((CssQuantity)cc).subType != CssQuantity.Unit.LENGTH); // '1m' is invalid length
  }
  }
+
+ @Test
+ public void testParser015() throws Exception {
+ String s = "E { --my-property: 16px; } ";
+ HandlerImpl handler = checkBasics(exec(s));
+ assertEquals(0, handler.errors.size());
+ }
 
  @Test
  public void testParserAtRule001() throws Exception {
@@ -884,6 +891,11 @@ public void testParserFile004() throws Exception {
  checkBasics(execFile("counter-styles.css", false)); 
  }
 
+ @Test
+ public void testParserFile005() throws Exception {
+ checkBasics(execFile("custom-properties.css", false));
+ }
+
  @Test
  public void testGrammarToCssString001() throws Exception { 
  String s = "E {color:black}";

src/test/java/org/idpf/epubcheck/util/css/CssScannerTest.java

@@ -454,6 +454,17 @@ public void testLexerIdent_23() throws Exception {
  assertEquals("-a", tokens.get(0).getChars());
  }
 
+ @Test
+ public void testLexerIdent_30() throws Exception {
+ String s = "--a";
+
+ List<CssToken> tokens = execScan(s);
+ assertEquals(1, tokens.size());
+ assertEquals(0, exceptions.size());
+ assertEquals(CssToken.Type.IDENT, tokens.get(0).getType());
+ assertEquals("--a", tokens.get(0).getChars());
+ }
+
  @Test
  public void testLexerAtKeyword_10() throws Exception {
  String s = "@ident";

src/test/resources/css/custom-properties.css

@@ -0,0 +1,37 @@
+/*Examples taken from MDN "Using custom properties"*/
+
+/* Basics */
+
+:root {
+ --main-bg-color: brown;
+}
+
+.one {
+ color: white;
+ background-color: var(--main-bg-color);
+ margin: 10px;
+ width: 50px;
+ height: 50px;
+ display: inline-block;
+}
+
+
+/* Fallbacks */ 
+
+.two {
+ color: var(--my-var, red); /* Red if --my-var is not defined */
+}
+
+.three {
+ background-color: var(--my-var, var(--my-background, pink)); /* pink if my-var and --my-background are not defined */
+}
+
+.three {
+ background-color: var(--my-var, --my-background, pink); /* Invalid: "--my-background, pink" */
+}
+
+/* Invalid variable */
+
+:root { --text-color: 16px; } 
+p { color: blue; } 
+p { color: var(--text-color); }