Fix: prefer-const object destructuring false positive (fixes #9108) (#…

…10368)

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close #9108

**What is the purpose of this pull request? (put an "X" next to item)**

[ ] Documentation update
[x] Bug fix ([template](https://raw.githubusercontent.com/eslint/eslint/master/templates/bug-report.md))
[ ] New rule ([template](https://raw.githubusercontent.com/eslint/eslint/master/templates/rule-proposal.md))
[ ] Changes an existing rule ([template](https://raw.githubusercontent.com/eslint/eslint/master/templates/rule-change-proposal.md))
[ ] Add autofixing to a rule
[ ] Add a CLI option
[ ] Add something to the core
[ ] Other, please explain:

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#9108

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**What changes did you make? (Give an overview)**
Allow:
```js
(function ({ a }) {
  let b;
  ({ a, b } = obj);
})();
```
or
```js
let a;
{
  let b;
  ({ a, b } = obj);
}
```

lib/rules/prefer-const.js

@@ -5,6 +5,8 @@
 
 "use strict";
 
+const astUtils = require("../ast-utils");
+
 //------------------------------------------------------------------------------
 // Helpers
 //------------------------------------------------------------------------------
@@ -55,6 +57,54 @@ function canBecomeVariableDeclaration(identifier) {
     );
 }
 
+/**
+ * Checks if an property or element is from outer scope or function parameters
+ * in destructing pattern.
+ *
+ * @param {string} name - A variable name to be checked.
+ * @param {eslint-scope.Scope} initScope - A scope to start find.
+ * @returns {boolean} Indicates if the variable is from outer scope or function parameters.
+ */
+function isOuterVariableInDestructing(name, initScope) {
+    if (initScope.through.find(ref => ref.resolved && ref.resolved.name === name)) {
+        return true;
+    }
+
+    const variable = astUtils.getVariableByName(initScope, name);
+
+    if (variable !== null) {
+        return variable.defs.some(def => def.type === "Parameter");
+    }
+
+    return false;
+}
+
+/**
+ * Gets the VariableDeclarator/AssignmentExpression node that a given reference
+ * belongs to.
+ * This is used to detect a mix of reassigned and never reassigned in a
+ * destructuring.
+ *
+ * @param {eslint-scope.Reference} reference - A reference to get.
+ * @returns {ASTNode|null} A VariableDeclarator/AssignmentExpression node or
+ *      null.
+ */
+function getDestructuringHost(reference) {
+    if (!reference.isWrite()) {
+        return null;
+    }
+    let node = reference.identifier.parent;
+
+    while (PATTERN_TYPE.test(node.type)) {
+        node = node.parent;
+    }
+
+    if (!DESTRUCTURING_HOST_TYPE.test(node.type)) {
+        return null;
+    }
+    return node;
+}
+
 /**
  * Gets an identifier node of a given variable.
  *
@@ -102,6 +152,32 @@ function getIdentifierIfShouldBeConst(variable, ignoreReadBeforeAssign) {
             if (isReassigned) {
                 return null;
             }
+
+            const destructuringHost = getDestructuringHost(reference);
+
+            if (destructuringHost !== null && destructuringHost.left !== void 0) {
+                const leftNode = destructuringHost.left;
+                let hasOuterVariables = false;
+
+                if (leftNode.type === "ObjectPattern") {
+                    const properties = leftNode.properties;
+
+                    hasOuterVariables = properties
+                        .filter(prop => prop.value)
+                        .map(prop => prop.value.name)
+                        .some(name => isOuterVariableInDestructing(name, variable.scope));
+                } else if (leftNode.type === "ArrayPattern") {
+                    const elements = leftNode.elements;
+
+                    hasOuterVariables = elements
+                        .map(element => element.name)
+                        .some(name => isOuterVariableInDestructing(name, variable.scope));
+                }
+                if (hasOuterVariables) {
+                    return null;
+                }
+            }
+
             writer = reference;
 
         } else if (reference.isRead() && writer === null) {
@@ -131,32 +207,6 @@ function getIdentifierIfShouldBeConst(variable, ignoreReadBeforeAssign) {
     return writer.identifier;
 }
 
-/**
- * Gets the VariableDeclarator/AssignmentExpression node that a given reference
- * belongs to.
- * This is used to detect a mix of reassigned and never reassigned in a
- * destructuring.
- *
- * @param {eslint-scope.Reference} reference - A reference to get.
- * @returns {ASTNode|null} A VariableDeclarator/AssignmentExpression node or
- *      null.
- */
-function getDestructuringHost(reference) {
-    if (!reference.isWrite()) {
-        return null;
-    }
-    let node = reference.identifier.parent;
-
-    while (PATTERN_TYPE.test(node.type)) {
-        node = node.parent;
-    }
-
-    if (!DESTRUCTURING_HOST_TYPE.test(node.type)) {
-        return null;
-    }
-    return node;
-}
-
 /**
  * Groups by the VariableDeclarator/AssignmentExpression node that each
  * reference of given variables belongs to.
@@ -290,7 +340,7 @@ module.exports = {
                     (varDeclParent.parent.type === "ForInStatement" || varDeclParent.parent.type === "ForOfStatement" || varDeclParent.declarations[0].init) &&
 
                     /*
-                     * If options.destucturing is "all", then this warning will not occur unless
+                     * If options.destructuring is "all", then this warning will not occur unless
                      * every assignment in the destructuring should be const. In that case, it's safe
                      * to apply the fix.
                      */

tests/lib/rules/prefer-const.js

@@ -69,6 +69,22 @@ ruleTester.run("prefer-const", rule, {
         "/*exported a*/ let a; function init() { a = foo(); }",
         "/*exported a*/ let a = 1",
         "let a; if (true) a = 0; foo(a);",
+        `
+        (function (a) {
+            let b;
+            ({ a, b } = obj);
+        })();
+        `,
+        `
+        (function (a) {
+            let b;
+            ([ a, b ] = obj);
+        })();
+        `,
+        "var a; { var b; ({ a, b } = obj); }",
+        "let a; { let b; ({ a, b } = obj); }",
+        "var a; { var b; ([ a, b ] = obj); }",
+        "let a; { let b; ([ a, b ] = obj); }",
 
         /*
          * The assignment is located in a different scope.