From 1dfe077b7e47c6090277eb984e08bd472bb5595e Mon Sep 17 00:00:00 2001
From: Toru Nagashima <star.ctor@gmail.com>
Date: Fri, 19 Apr 2019 15:50:23 +0900
Subject: [PATCH] Fix: autofix of no-unneeded-ternary made syntax error (fixes
 #11579) (#11616)

---
 lib/rules/no-unneeded-ternary.js       | 20 +++---
 tests/lib/rules/no-unneeded-ternary.js | 84 ++++++++++++++++++++++++++
 2 files changed, 95 insertions(+), 9 deletions(-)

diff --git a/lib/rules/no-unneeded-ternary.js b/lib/rules/no-unneeded-ternary.js
index e75a36430fe..4dbb78a3e07 100644
--- a/lib/rules/no-unneeded-ternary.js
+++ b/lib/rules/no-unneeded-ternary.js
@@ -17,6 +17,7 @@ const OPERATOR_INVERSES = {
 
     // Operators like < and >= are not true inverses, since both will return false with NaN.
 };
+const OR_PRECEDENCE = astUtils.getPrecedence({ type: "LogicalExpression", operator: "||" });
 
 //------------------------------------------------------------------------------
 // Rule Definition
@@ -141,15 +142,16 @@ module.exports = {
                         loc: node.consequent.loc.start,
                         message: "Unnecessary use of conditional expression for default assignment.",
                         fix: fixer => {
-                            let nodeAlternate = astUtils.getParenthesisedText(sourceCode, node.alternate);
-
-                            if (node.alternate.type === "ConditionalExpression" || node.alternate.type === "YieldExpression") {
-                                const isAlternateParenthesised = astUtils.isParenthesised(sourceCode, node.alternate);
-
-                                nodeAlternate = isAlternateParenthesised ? nodeAlternate : `(${nodeAlternate})`;
-                            }
-
-                            return fixer.replaceText(node, `${astUtils.getParenthesisedText(sourceCode, node.test)} || ${nodeAlternate}`);
+                            const shouldParenthesizeAlternate = (
+                                astUtils.getPrecedence(node.alternate) < OR_PRECEDENCE &&
+                                !astUtils.isParenthesised(sourceCode, node.alternate)
+                            );
+                            const alternateText = shouldParenthesizeAlternate
+                                ? `(${sourceCode.getText(node.alternate)})`
+                                : astUtils.getParenthesisedText(sourceCode, node.alternate);
+                            const testText = astUtils.getParenthesisedText(sourceCode, node.test);
+
+                            return fixer.replaceText(node, `${testText} || ${alternateText}`);
                         }
                     });
                 }
diff --git a/tests/lib/rules/no-unneeded-ternary.js b/tests/lib/rules/no-unneeded-ternary.js
index badf529e66d..5196b576bd0 100644
--- a/tests/lib/rules/no-unneeded-ternary.js
+++ b/tests/lib/rules/no-unneeded-ternary.js
@@ -230,6 +230,90 @@ ruleTester.run("no-unneeded-ternary", rule, {
                 line: 1,
                 column: 24
             }]
+        },
+        {
+            code: "var a = b ? b : c => c;",
+            output: "var a = b || (c => c);",
+            options: [{ defaultAssignment: false }],
+            parserOptions: { ecmaVersion: 2015 },
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 13
+            }]
+        },
+        {
+            code: "var a = b ? b : c = 0;",
+            output: "var a = b || (c = 0);",
+            options: [{ defaultAssignment: false }],
+            parserOptions: { ecmaVersion: 2015 },
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 13
+            }]
+        },
+        {
+            code: "var a = b ? b : (c => c);",
+            output: "var a = b || (c => c);",
+            options: [{ defaultAssignment: false }],
+            parserOptions: { ecmaVersion: 2015 },
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 13
+            }]
+        },
+        {
+            code: "var a = b ? b : (c = 0);",
+            output: "var a = b || (c = 0);",
+            options: [{ defaultAssignment: false }],
+            parserOptions: { ecmaVersion: 2015 },
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 13
+            }]
+        },
+        {
+            code: "var a = b ? b : (c) => (c);",
+            output: "var a = b || ((c) => (c));",
+            options: [{ defaultAssignment: false }],
+            parserOptions: { ecmaVersion: 2015 },
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 13
+            }]
+        },
+        {
+            code: "var a = b ? b : c, d; // this is ((b ? b : c), (d))",
+            output: "var a = b || c, d; // this is ((b ? b : c), (d))",
+            options: [{ defaultAssignment: false }],
+            parserOptions: { ecmaVersion: 2015 },
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 13
+            }]
+        },
+        {
+            code: "var a = b ? b : (c, d);",
+            output: "var a = b || (c, d);",
+            options: [{ defaultAssignment: false }],
+            parserOptions: { ecmaVersion: 2015 },
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 13
+            }]
         }
     ]
 });