Bug 1502185 - Don't allow auto in grid line names. r=mats

See w3c/csswg-drafts#2856.

Differential Revision: https://phabricator.services.mozilla.com/D9882

--HG--
extra : moz-landing-system : lando

layout/style/test/property_database.js

@@ -6687,7 +6687,7 @@ gCSSProperties["grid-template-columns"] = {
 if (isGridTemplateSubgridValueEnabled) {
   gCSSProperties["grid-template-columns"].other_values.push(
     // See https://bugzilla.mozilla.org/show_bug.cgi?id=981300
-    "[none auto subgrid min-content max-content foo] 40px",
+    "[none subgrid min-content max-content foo] 40px",
 
     "subgrid",
     "subgrid [] [foo bar]",

servo/components/style/values/generics/grid.rs

@@ -120,7 +120,9 @@ impl Parse for GridLine<specified::Integer> {
                 if val_before_span || grid_line.ident.is_some() {
                     return Err(location.new_custom_error(StyleParseErrorKind::UnspecifiedError));
                 }
-                grid_line.ident = Some(CustomIdent::from_ident(location, &name, &[])?);
+                // NOTE(emilio): `span` is consumed above, so we only need to
+                // reject `auto`.
+                grid_line.ident = Some(CustomIdent::from_ident(location, &name, &["auto"])?);
             } else {
                 break;
             }

servo/components/style/values/specified/grid.rs

@@ -95,7 +95,7 @@ pub fn parse_line_names<'i, 't>(
         while let Ok((loc, ident)) = input.try(|i| -> Result<_, CssParseError<()>> {
             Ok((i.current_source_location(), i.expect_ident_cloned()?))
         }) {
-            let ident = CustomIdent::from_ident(loc, &ident, &["span"])?;
+            let ident = CustomIdent::from_ident(loc, &ident, &["span", "auto"])?;
             values.push(ident);
         }