visitor: add delete-unreachable-code and delete-nested-blocks

Signed-off-by: echo094 <20028238+echo094@users.noreply.github.com>

Author: echo094

src/plugin/common.js

@@ -10,8 +10,10 @@ module.exports = function (code) {
     console.error(`Cannot parse code: ${e.reasonCode}`)
     return null
   }
-  const deleteExtra = require('../visitor/delete-extra')
-  traverse(ast, deleteExtra)
+  const deleteUnreachableCode = require('../visitor/delete-unreachable-code')
+  traverse(ast, deleteUnreachableCode)
+  const deleteNestedBlocks = require('../visitor/delete-nested-blocks')
+  traverse(ast, deleteNestedBlocks)
   const calculateConstantExp = require('../visitor/calculate-constant-exp')
   traverse(ast, calculateConstantExp)
   const calculateRString = require('../visitor/calculate-rstring')

src/visitor/delete-nested-blocks.js

@@ -0,0 +1,33 @@
+const isIntersect = (path, bindings) => {
+  path.scope.crawl()
+  for (const key of Object.keys(bindings)) {
+    if (path.scope.hasBinding(key)) {
+      return true
+    }
+  }
+  return false
+}
+
+/**
+ * Avoid nested blocks.
+ *
+ * This is slightly different from the @putout/plugin-remove-nested-blocks :
+ * https://github.com/coderaiser/putout/issues/224#issuecomment-2614051528
+ */
+module.exports = {
+  BlockStatement: (path) => {
+    const { parentPath } = path
+    if (!parentPath.isBlockStatement() && !parentPath.isProgram()) {
+      return
+    }
+    let valid = path.container.length === 1
+    if (!isIntersect(parentPath, path.scope.bindings)) {
+      valid = true
+    }
+    if (!valid) {
+      return
+    }
+    path.replaceWithMultiple(path.node.body)
+    path.scope.crawl()
+  },
+}

src/visitor/delete-unreachable-code.js

@@ -0,0 +1,50 @@
+const t = require('@babel/types')
+
+/**
+ * DFS the BlockStatement to find and return the location of the first
+ * ReturnStatement, which is not inside a Conditional Block.
+ */
+const checkReturnLocation = (body) => {
+  for (let i = 0; i < body.length; ++i) {
+    if (t.isReturnStatement(body[i])) {
+      return i
+    }
+    if (t.isBlockStatement(body[i])) {
+      const ret = checkReturnLocation(body[i].body)
+      if (~ret) {
+        return i
+      }
+    }
+  }
+  return -1
+}
+
+/**
+ * Remove the codes after the first ReturnStatement, which is not inside a
+ * Conditional Block. The FunctionDeclaration will be preserved.
+ *
+ * This is slightly different from the @putout/plugin-remove-unreachable-code :
+ * https://github.com/coderaiser/putout/issues/224#issuecomment-2614051528
+ */
+module.exports = {
+  BlockStatement: (path) => {
+    const body = path.node.body
+    const loc = checkReturnLocation(body)
+    if (loc == -1) {
+      return
+    }
+    for (let i = body.length - 1; i > loc; --i) {
+      if (t.isFunctionDeclaration(body[i])) {
+        continue
+      }
+      body.splice(i, 1)
+    }
+    if (loc === 0 && t.isBlockStatement(body[0])) {
+      const inner = body.shift()
+      while (inner.body.length) {
+        body.unshift(inner.body.pop())
+      }
+    }
+    path.scope.crawl()
+  },
+}