Major performance fix for certain css selectors

packages/imba/changelog.md

@@ -2,9 +2,21 @@
 
 ## Unreleased
 
+* Major performance fix for certain css selectors.
+
+    When using selectors like `^@hover prop:value` Imba would compile
+    the selector to `:is(:hover).some-class > target { prop:value }`.
+    The fact that `:is(:hover)` is placed before the class can cause
+    the browser to recalculate styles for a huge part of the document
+    when pointer crosses between elements.
+
+    Rewriting the compiled selector to `.some-class:is(:hover) > target`
+    makes this issue go away completely. If you ever use selectors like
+    this it is highly recommended to update.
+
 * Fix tooling for `item isa (a or b or c)` syntax
 
-* Fix tooling for tags inside if/else trees
+* Fix tooling for tags inside
 
 * Fix sourcemapping for tag declaration superclass
 

packages/imba/src/compiler/selparse.imba

@@ -4,7 +4,7 @@ import {modifiers} from './theme.imba'
 
 def addClass rule, name
 	# TODO check for negs as well?
-	rule.push({flag: name})
+	rule.unshift({flag: name})
 	# rule.classNames ||= []
 	# if rule.classNames.indexOf(name) == -1
 	# 	rule.classNames.push(name)