Fix: prefer-const autofix multiline assignment (fixes eslint#10582)

sstern6 · Oct 21, 2018 · c1fdf77 · c1fdf77
1 parent 58ff359
commit c1fdf77
Show file tree

Hide file tree

Showing 2 changed files with 87 additions and 7 deletions.
diff --git a/lib/rules/prefer-const.js b/lib/rules/prefer-const.js
@@ -357,6 +357,9 @@ module.exports = {
         const shouldMatchAnyDestructuredVariable = options.destructuring !== "all";
         const ignoreReadBeforeAssign = options.ignoreReadBeforeAssign === true;
         const variables = [];
+        let reportCount = 0;
+        const firstIdentifier = sourceCode.ast.tokens.find(node => node.type === "Identifier");
+        let name = firstIdentifier && firstIdentifier.length > 0 ? firstIdentifier.value : "";
 
         /**
          * Reports given identifier nodes if all of the nodes should be declared
@@ -377,14 +380,41 @@ module.exports = {
 
             if (nodes.length && (shouldMatchAnyDestructuredVariable || nodesToReport.length === nodes.length)) {
                 const varDeclParent = findUp(nodes[0], "VariableDeclaration", parentNode => parentNode.type.endsWith("Statement"));
-                const shouldFix = varDeclParent &&
+                const isVarDecParentNull = varDeclParent === null;
+
+                if (!isVarDecParentNull && varDeclParent.declarations.length > 0) {
+                    const firstDeclaration = varDeclParent.declarations[0];
+
+                    if (firstDeclaration.init) {
+                        const firstDecParent = firstDeclaration.init.parent;
+
+                        /*
+                         * First we check the declaration type and then depending on
+                         * if the type is a "VariableDeclarator" or its an "ObjectPattern"
+                         * we compare the name from the first identifier, if the names are different
+                         * we assign the new name and reset the count of reportCount and nodeCount in
+                         * order to check each block for the number of reported errors and base our fix
+                         * based on comparing nodes.length and nodesToReport.length.
+                         */
+
+                        if (firstDecParent.type === "VariableDeclarator") {
+
+                            if (firstDecParent.id.name !== name) {
+                                name = firstDecParent.id.name;
+                                reportCount = 0;
+                            }
+
+                            if (firstDecParent.id.type === "ObjectPattern") {
+                                if (firstDecParent.init.name !== name) {
+                                    name = firstDecParent.init.name;
+                                    reportCount = 0;
+                                }
+                            }
+                        }
+                    }
+                }
 
-                    /*
-                     * If there are multiple variable declarations, like {let a = 1, b = 2}, then
-                     * do not attempt to fix if one of the declarations should be `const`. It's
-                     * too hard to know how the developer would want to automatically resolve the issue.
-                     */
-                    varDeclParent.declarations.length === 1 &&
+                let shouldFix = varDeclParent &&
 
                     // Don't do a fix unless the variable is initialized (or it's in a for-in or for-of loop)
                     (varDeclParent.parent.type === "ForInStatement" || varDeclParent.parent.type === "ForOfStatement" || varDeclParent.declarations[0].init) &&
@@ -396,6 +426,21 @@ module.exports = {
                      */
                     nodesToReport.length === nodes.length;
 
+                if (!isVarDecParentNull && varDeclParent.declarations && varDeclParent.declarations.length !== 1) {
+
+                    if (varDeclParent && varDeclParent.declarations && varDeclParent.declarations.length >= 1) {
+
+                        /*
+                         * Add nodesToReport.length to a count, then comparing the count to the length
+                         * of the declarations in the current block.
+                         */
+
+                        reportCount += nodesToReport.length;
+
+                        shouldFix = shouldFix && (reportCount === varDeclParent.declarations.length);
+                    }
+                }
+
                 nodesToReport.forEach(node => {
                     context.report({
                         node,

diff --git a/tests/lib/rules/prefer-const.js b/tests/lib/rules/prefer-const.js
@@ -454,6 +454,41 @@ ruleTester.run("prefer-const", rule, {
             errors: [
                 { message: "'predicate' is never reassigned. Use 'const' instead.", type: "Identifier" }
             ]
+        },
+        {
+            code: "let x = 'x', y = 'y';",
+            output: "const x = 'x', y = 'y';",
+            errors: [
+                { message: "'x' is never reassigned. Use 'const' instead.", type: "Identifier" },
+                { message: "'y' is never reassigned. Use 'const' instead.", type: "Identifier" }
+            ]
+        },
+        {
+            code: "let x = 'x', y = 'y'; x = 1",
+            output: null,
+            errors: [
+                { message: "'y' is never reassigned. Use 'const' instead.", type: "Identifier" }
+            ]
+        },
+        {
+            code: "let x = 1, y = 'y'; let z = 1;",
+            output: "const x = 1, y = 'y'; const z = 1;",
+            errors: [
+                { message: "'x' is never reassigned. Use 'const' instead.", type: "Identifier" },
+                { message: "'y' is never reassigned. Use 'const' instead.", type: "Identifier" },
+                { message: "'z' is never reassigned. Use 'const' instead.", type: "Identifier" }
+            ]
+        },
+        {
+            code: "let { a, b, c} = obj; let { x, y, z} = anotherObj; x = 2;",
+            output: "const { a, b, c} = obj; let { x, y, z} = anotherObj; x = 2;",
+            errors: [
+                { message: "'a' is never reassigned. Use 'const' instead.", type: "Identifier" },
+                { message: "'b' is never reassigned. Use 'const' instead.", type: "Identifier" },
+                { message: "'c' is never reassigned. Use 'const' instead.", type: "Identifier" },
+                { message: "'y' is never reassigned. Use 'const' instead.", type: "Identifier" },
+                { message: "'z' is never reassigned. Use 'const' instead.", type: "Identifier" }
+            ]
         }
 
     ]