swap checks, only compute path when absolutely necessary

We are checking wether the to-be-replaced ast is a complex selector or
not. If it is, only then do we care about the type of the grand parent
selector.

Author: RobinMalfait

packages/tailwindcss/src/ast.ts

@@ -847,46 +847,47 @@ export function handleNesting(ast: AstNode[]): AstNode[] {
                       //           ^^^^^^^^^^^^^^^^^   complex selector
                       //
                       else if (ctx.parent.kind === 'compound') {
-                        let path = ctx.path()
-                        let grandParent = path[path.length - 2]
+                        if (parentAst[0].kind === 'complex') {
+                          let path = ctx.path()
+                          let grandParent = path[path.length - 2]
 
-                        if (
-                          grandParent &&
-                          grandParent.kind === 'complex' &&
-                          // When our compound parent is part of a complex
-                          // selector, and it's not the very first node, then we
-                          // can't safely get rid of the `:is(…)` if the last
-                          // selector is a complex selector as well, unless the
-                          // `&` maps to a single selector or compound selector.
-                          //
-                          // ```css
-                          // .foo .bar {            /* Complex selector */
-                          //   .system &:focus {    /* Complex selector + compound selecto*/
-                          //     --x: 1;
-                          //   }
-                          // }
-                          // .foo:hover {           /* Compound selector */
-                          //   .system &:focus {    /* Complex selector + compound selector */
-                          //     --x: 2;
-                          //   }
-                          // }
-                          // ```
-                          //
-                          // ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓
-                          //
-                          // ```css
-                          // .system :is(.foo .bar):focus { /* Cannot drop the `:is(…)`, otherwise `.system` and `.foo` can be swapped in the DOM */
-                          //   --x: 1;
-                          // }
-                          // .system .foo:hover:focus {
-                          //   --x: 2;
-                          // }
-                          // ```
-                          //
-                          grandParent.nodes[0] !== ctx.parent &&
-                          parentAst[0].kind === 'complex'
-                        ) {
-                          return // Keep `:is(…)` semantics
+                          if (
+                            grandParent &&
+                            grandParent.kind === 'complex' &&
+                            // When our compound parent is part of a complex
+                            // selector, and it's not the very first node, then we
+                            // can't safely get rid of the `:is(…)` if the last
+                            // selector is a complex selector as well, unless the
+                            // `&` maps to a single selector or compound selector.
+                            //
+                            // ```css
+                            // .foo .bar {            /* Complex selector */
+                            //   .system &:focus {    /* Complex selector + compound selecto*/
+                            //     --x: 1;
+                            //   }
+                            // }
+                            // .foo:hover {           /* Compound selector */
+                            //   .system &:focus {    /* Complex selector + compound selector */
+                            //     --x: 2;
+                            //   }
+                            // }
+                            // ```
+                            //
+                            // ↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓↓
+                            //
+                            // ```css
+                            // .system :is(.foo .bar):focus { /* Cannot drop the `:is(…)`, otherwise `.system` and `.foo` can be swapped in the DOM */
+                            //   --x: 1;
+                            // }
+                            // .system .foo:hover:focus {
+                            //   --x: 2;
+                            // }
+                            // ```
+                            //
+                            grandParent.nodes[0] !== ctx.parent
+                          ) {
+                            return // Keep `:is(…)` semantics
+                          }
                         }
 
                         // `&*` and `&div` are invalid CSS so these should stay