use direct replacements if possible

Instead of always calling `.splice()`, there are cases where if we
replace a node with a single other note that we can replace it directly
without using `splice(…)`.

packages/tailwindcss/src/ast.ts

@@ -143,7 +143,18 @@ export function walk(
         context,
         path,
         replaceWith(newNode) {
-          ast.splice(i, 1, ...(Array.isArray(newNode) ? newNode : [newNode]))
+          if (Array.isArray(newNode)) {
+            if (newNode.length === 0) {
+              ast.splice(i, 1)
+            } else if (newNode.length === 1) {
+              ast[i] = newNode[0]
+            } else {
+              ast.splice(i, 1, ...newNode)
+            }
+          } else {
+            ast[i] = newNode
+          }
+
           // We want to visit the newly replaced node(s), which start at the
           // current index (i). By decrementing the index here, the next loop
           // will process this position (containing the replaced node) again.
@@ -204,7 +215,17 @@ export function walkDepth(
       context,
       path,
       replaceWith(newNode) {
-        ast.splice(i, 1, ...newNode)
+        if (Array.isArray(newNode)) {
+          if (newNode.length === 0) {
+            ast.splice(i, 1)
+          } else if (newNode.length === 1) {
+            ast[i] = newNode[0]
+          } else {
+            ast.splice(i, 1, ...newNode)
+          }
+        } else {
+          ast[i] = newNode
+        }
 
         // Skip over the newly inserted nodes (being depth-first it doesn't make sense to visit them)
         i += newNode.length - 1

packages/tailwindcss/src/compat/selector-parser.ts

@@ -96,7 +96,18 @@ export function walk(
       visit(node, {
         parent,
         replaceWith(newNode) {
-          ast.splice(i, 1, ...(Array.isArray(newNode) ? newNode : [newNode]))
+          if (Array.isArray(newNode)) {
+            if (newNode.length === 0) {
+              ast.splice(i, 1)
+            } else if (newNode.length === 1) {
+              ast[i] = newNode[0]
+            } else {
+              ast.splice(i, 1, ...newNode)
+            }
+          } else {
+            ast[i] = newNode
+          }
+
           // We want to visit the newly replaced node(s), which start at the
           // current index (i). By decrementing the index here, the next loop
           // will process this position (containing the replaced node) again.

packages/tailwindcss/src/value-parser.ts

@@ -67,7 +67,18 @@ export function walk(
       visit(node, {
         parent,
         replaceWith(newNode) {
-          ast.splice(i, 1, ...(Array.isArray(newNode) ? newNode : [newNode]))
+          if (Array.isArray(newNode)) {
+            if (newNode.length === 0) {
+              ast.splice(i, 1)
+            } else if (newNode.length === 1) {
+              ast[i] = newNode[0]
+            } else {
+              ast.splice(i, 1, ...newNode)
+            }
+          } else {
+            ast[i] = newNode
+          }
+
           // We want to visit the newly replaced node(s), which start at the
           // current index (i). By decrementing the index here, the next loop
           // will process this position (containing the replaced node) again.