fix: fix false positive of prefer-flat-map when flattening with depth != 1 (fixes #61)

Author: freaktechnik

README.md

@@ -196,6 +196,8 @@ This rule is auto fixable.
 Code that triggers this rule:
 ```js
 const flattenedAndMapped = array.map((p) => p).flat();
+
+const flatWithDefaultDepth = array.map((r) => r).flat(1);
 ```
 
 Code that doesn't trigger this rule:
@@ -209,6 +211,8 @@ const mapped = array.map((r) => r + 1);
 const mappedThenFlattened = array.flat().map((r) => r + 1);
 
 const flatMappedWithExtra = array.map((r) => r + 1).reverse().flat();
+
+const flatWithDepth = array.map((p) => p).flat(99);
 ```
 
 ### `prefer-flat`

rules/prefer-flat-map.js

@@ -16,7 +16,7 @@ module.exports = {
     },
     create(context) {
         return {
-            'CallExpression[callee.type="MemberExpression"] > MemberExpression[property.name="flat"] > CallExpression[callee.type="MemberExpression"][callee.property.name="map"]'(node) {
+            'CallExpression[callee.type="MemberExpression"]:matches([arguments.length=0],[arguments.0.type="Literal"][arguments.0.value=1]) > MemberExpression[property.name="flat"] > CallExpression[callee.type="MemberExpression"][callee.property.name="map"]'(node) {
                 const parent = node,
                     callee = node.parent;
                 node = callee.parent;

test/rules/prefer-flat-map.js

@@ -14,7 +14,8 @@ ruleTester.run('prefer-flat-map', rule, {
         'array.flat()',
         'array.map((r) => r + 1)',
         'array.flat().map((r) => r + 1)',
-        'array.map((r) => r + 1).reverse().flat()'
+        'array.map((r) => r + 1).reverse().flat()',
+        'array.map((p) => p).flat(99)'
     ],
     invalid: [
         {
@@ -34,6 +35,15 @@ ruleTester.run('prefer-flat-map', rule, {
                 line: 1
             } ],
             output: 'foo(); array.flatMap((p) => p); test();'
+        },
+        {
+            code: 'array.map((r) => r).flat(1)',
+            errors: [ {
+                message: 'Use flatMap instead of .map().flat()',
+                column: 7,
+                line: 1
+            } ],
+            output: 'array.flatMap((r) => r)'
         }
     ]
 });