refactor(compiler-core): follow up on #276

packages/compiler-core/src/parse.ts

@@ -564,12 +564,9 @@ function parseAttribute(
       )
       let content = match[2]
       let isStatic = true
-      // Non-dynamic arg is a constant.
-      let isConstant = true
 
       if (content.startsWith('[')) {
         isStatic = false
-        isConstant = false
 
         if (!content.endsWith(']')) {
           emitError(
@@ -585,7 +582,7 @@ function parseAttribute(
         type: NodeTypes.SIMPLE_EXPRESSION,
         content,
         isStatic,
-        isConstant,
+        isConstant: isStatic,
         loc
       }
     }
@@ -611,7 +608,8 @@ function parseAttribute(
         type: NodeTypes.SIMPLE_EXPRESSION,
         content: value.content,
         isStatic: false,
-        // Set `isConstant` to false by default and will decide in transformExpression
+        // Treat as non-constant by default. This can be potentially set to
+        // true by `transformExpression` to make it eligible for hoisting.
         isConstant: false,
         loc: value.loc
       },

packages/compiler-core/src/transforms/transformExpression.ts

@@ -91,6 +91,9 @@ export function processExpression(
       !literalsWhitelist.has(rawExp)
     ) {
       node.content = `_ctx.${rawExp}`
+    } else if (!context.identifiers[rawExp]) {
+      // mark node constant for hoisting unless it's referring a scope variable
+      node.isConstant = true
     }
     return node
   }
@@ -109,13 +112,13 @@ export function processExpression(
   const ids: (Identifier & PrefixMeta)[] = []
   const knownIds = Object.create(context.identifiers)
 
-  let isConstant = true
   // walk the AST and look for identifiers that need to be prefixed with `_ctx.`.
   walkJS(ast, {
     enter(node: Node & PrefixMeta, parent) {
       if (node.type === 'Identifier') {
         if (!ids.includes(node)) {
-          if (!knownIds[node.name] && shouldPrefix(node, parent)) {
+          const needPrefix = shouldPrefix(node, parent)
+          if (!knownIds[node.name] && needPrefix) {
             if (isPropertyShorthand(node, parent)) {
               // property shorthand like { foo }, we need to add the key since we
               // rewrite the value
@@ -123,14 +126,11 @@ export function processExpression(
             }
             node.name = `_ctx.${node.name}`
             node.isConstant = false
-            isConstant = false
             ids.push(node)
           } else if (!isStaticPropertyKey(node, parent)) {
-            // This means this identifier is pointing to a scope variable (a v-for alias, or a v-slot prop)
-            // which is also dynamic and cannot be hoisted.
-            node.isConstant = !(
-              knownIds[node.name] && shouldPrefix(node, parent)
-            )
+            // The identifier is considered constant unless it's pointing to a
+            // scope variable (a v-for alias, or a v-slot prop)
+            node.isConstant = !(needPrefix && knownIds[node.name])
             // also generate sub-expressions for other identifiers for better
             // source map support. (except for property keys which are static)
             ids.push(node)
@@ -220,7 +220,7 @@ export function processExpression(
     ret = createCompoundExpression(children, node.loc)
   } else {
     ret = node
-    ret.isConstant = isConstant
+    ret.isConstant = true
   }
   ret.identifiers = Object.keys(knownIds)
   return ret