Docs: fix doc for no-unneeded-ternary rule (fixes #12098) (#12410)

* Docs: fix docs for no-unneeded-ternary (fixes #12098)

* Update: add test cases
- default assignment on right hand side
- default assignment not on right side
- assignment that is not default e.g. x ? 1 : x

* Update doc for clarity

docs/rules/no-unneeded-ternary.md

@@ -41,8 +41,6 @@ Examples of **incorrect** code for this rule:
 var a = x === 2 ? true : false;
 
 var a = x ? true : false;
-
-var a = f(x ? x : 1);
 ```
 
 Examples of **correct** code for this rule:
@@ -58,7 +56,7 @@ var a = x ? "Yes" : "No";
 
 var a = x ? y : x;
 
-var a = x ? x : 1;  // Note that this is only allowed as it on the right hand side of an assignment; this type of ternary is disallowed everywhere else. See defaultAssignment option below for more details.
+f(x ? x : 1); // default assignment - would be disallowed if defaultAssignment option set to false. See option details below.
 ```
 
 ## Options
@@ -70,16 +68,20 @@ This rule has an object option:
 
 ### defaultAssignment
 
-The defaultAssignment option allows expressions of the form `x ? x : expr` (where `x` is any identifier and `expr` is any expression) as the right hand side of assignments (but nowhere else).
+When set to `true`, which it is by default, The defaultAssignment option allows expressions of the form `x ? x : expr` (where `x` is any identifier and `expr` is any expression).
 
 Examples of additional **incorrect** code for this rule with the `{ "defaultAssignment": false }` option:
 
 ```js
 /*eslint no-unneeded-ternary: ["error", { "defaultAssignment": false }]*/
 
 var a = x ? x : 1;
+
+f(x ? x : 1);
 ```
 
+Note that `defaultAssignment: false` still allows expressions of the form `x ? expr : x` (where the identifier is on the right hand side of the ternary).
+
 ## When Not To Use It
 
 You can turn this rule off if you are not concerned with unnecessary complexity in conditional expressions.

tests/lib/rules/no-unneeded-ternary.js

@@ -27,13 +27,23 @@ ruleTester.run("no-unneeded-ternary", rule, {
         "var a = x === 2 ? 'true' : 'false';",
         "var a = foo ? foo : bar;",
         "var value = 'a';var canSet = true;var result = value || (canSet ? 'unset' : 'can not set')",
+        "var a = foo ? bar : foo;",
+        "foo ? bar : foo;",
+        "var a = f(x ? x : 1)",
+        "f(x ? x : 1);",
+        "foo ? foo : bar;",
+        "var a = foo ? 'Yes' : foo;",
         {
             code: "var a = foo ? 'Yes' : foo;",
             options: [{ defaultAssignment: false }]
         },
         {
             code: "var a = foo ? bar : foo;",
             options: [{ defaultAssignment: false }]
+        },
+        {
+            code: "foo ? bar : foo;",
+            options: [{ defaultAssignment: false }]
         }
     ],
     invalid: [
@@ -314,6 +324,39 @@ ruleTester.run("no-unneeded-ternary", rule, {
                 line: 1,
                 column: 13
             }]
+        },
+        {
+            code: "f(x ? x : 1);",
+            output: "f(x || 1);",
+            options: [{ defaultAssignment: false }],
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 7
+            }]
+        },
+        {
+            code: "x ? x : 1;",
+            output: "x || 1;",
+            options: [{ defaultAssignment: false }],
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 5
+            }]
+        },
+        {
+            code: "var a = foo ? foo : bar;",
+            output: "var a = foo || bar;",
+            options: [{ defaultAssignment: false }],
+            errors: [{
+                message: "Unnecessary use of conditional expression for default assignment.",
+                type: "ConditionalExpression",
+                line: 1,
+                column: 15
+            }]
         }
     ]
 });