feature: @putout/plugin-conditions: merge-if-with-else

Author: coderaiser

README.md

@@ -1497,6 +1497,18 @@ isFn(1);
 
 </details>
 
+<details><summary>merge <code>if</code> with <code>else</code></summary>
+
+```diff
+-if (!matchFn)
++if (!matchFn || matchFn(options))
+    fix(from, to, path);
+-else if (matchFn(options))
+-   fix(from, to, path);
+```
+
+</details>
+
 <details><summary>convert <code>anonymous</code> to <code>arrow function</code></summary>
 
 ```diff

packages/plugin-conditions/README.md

@@ -22,6 +22,7 @@ npm i @putout/plugin-conditions -D
 - ✅ [convert-arrow-to-condition](#convert-arrow-to-condition);
 - ✅ [evaluate](#evaluate);
 - ✅ [merge-if-statements](#merge-if-statements);
+- ✅ [merge-if-with-else](#merge-if-with-else);
 - ✅ [reverse](#reverse);
 - ✅ [remove-boolean](#remove-boolean);
 - ✅ [remove-constant](#remove-constant);
@@ -53,6 +54,7 @@ npm i @putout/plugin-conditions -D
         "conditions/remove-useless-loop-condition": "on",
         "conditions/remove-same-values-condition": "on",
         "conditions/merge-if-statements": "on",
+        "conditions/merge-if-with-else": "on",
         "conditions/simplify": "on",
         "conditions/wrap-with-block": "on"
     }
@@ -352,7 +354,7 @@ alert('hello');
 
 ## merge-if-statements
 
-> The `if` statement executes a statement `if` a specified condition is truthy.
+> Multiple `if...else` statements can be nested to create an else if clause
 >
 > (c) [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/if...else)
 
@@ -371,6 +373,28 @@ if (a > b && b < c)
     console.log('hello');
 ```
 
+## merge-if-with-else
+
+> The `if` statement executes a statement `if` a specified condition is truthy.
+>
+> (c) [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/if...else)
+
+### ❌ Example of incorrect code
+
+```js
+if (!matchFn)
+    fix(from, to, path);
+else if (matchFn(options))
+    fix(from, to, path);
+```
+
+### ✅ Example of correct code
+
+```js
+if (!matchFn || matchFn(options))
+    fix(from, to, path);
+```
+
 ## remove-useless-else
 
 > You can skip the `else` block if your `if` block always executes a `return` statement, it makes code a lot easier to read.

packages/plugin-conditions/lib/index.js

@@ -17,6 +17,7 @@ const convertArrowToCondition = require('./convert-arrow-to-condition');
 const reverseCondition = require('./reverse-condition');
 const wrapWithBlock = require('./wrap-with-block');
 const removeUselessLoopCondition = require('./remove-useless-loop-condition');
+const mergeIfWithElse = require('./merge-if-with-else');
 
 module.exports.rules = {
     'apply-comparison-order': applyComparisonOrder,
@@ -36,4 +37,5 @@ module.exports.rules = {
     'reverse-condition': reverseCondition,
     'wrap-with-block': wrapWithBlock,
     'remove-useless-loop-condition': removeUselessLoopCondition,
+    'merge-if-with-else': mergeIfWithElse,
 };

packages/plugin-conditions/lib/merge-if-with-else/fixture/merge-if-with-else-fix.js

@@ -0,0 +1,2 @@
+if (!matchFn || matchFn(options))
+    fix(from, to, path);

packages/plugin-conditions/lib/merge-if-with-else/fixture/merge-if-with-else.js

@@ -0,0 +1,4 @@
+if (!matchFn)
+    fix(from, to, path);
+else if (matchFn(options))
+    fix(from, to, path);

packages/plugin-conditions/lib/merge-if-with-else/index.js

@@ -0,0 +1,27 @@
+'use strict';
+
+const {types, operator} = require('putout');
+
+const {compare} = operator;
+const {logicalExpression} = types;
+
+module.exports.report = () => `Merge 'if' with 'else' when the body is the same`;
+
+module.exports.fix = (path) => {
+    const {test: testFirst, alternate} = path.node;
+    const {test: testSecond} = alternate;
+    
+    path.node.test = logicalExpression('||', testFirst, testSecond);
+    delete path.node.alternate;
+};
+module.exports.traverse = ({push}) => ({
+    IfStatement: (path) => {
+        if (!path.node.alternate)
+            return;
+        
+        if (!compare(path.node.consequent, path.node.alternate.consequent))
+            return;
+        
+        push(path);
+    },
+});

packages/plugin-conditions/lib/merge-if-with-else/index.spec.js

@@ -0,0 +1,20 @@
+'use strict';
+
+const {createTest} = require('@putout/test');
+const plugin = require('.');
+
+const test = createTest(__dirname, {
+    plugins: [
+        ['merge-if-with-else', plugin],
+    ],
+});
+
+test('conditions: merge-if-with-else: report', (t) => {
+    t.report('merge-if-with-else', `Merge 'if' with 'else' when the body is the same`);
+    t.end();
+});
+
+test('conditions: merge-if-with-else: transform', (t) => {
+    t.transform('merge-if-with-else');
+    t.end();
+});

packages/plugin-conditions/test/conditions.js

@@ -93,3 +93,8 @@ test('plugin-conditions: transform: remove-useless-loop-condition', (t) => {
     t.transform('remove-useless-loop-condition');
     t.end();
 });
+
+test('plugin-conditions: transform: merge-if-with-else', (t) => {
+    t.transform('merge-if-with-else');
+    t.end();
+});

packages/plugin-conditions/test/fixture/merge-if-with-else-fix.js

@@ -0,0 +1,2 @@
+if (!matchFn || matchFn(options))
+    fix(from, to, path);

packages/plugin-conditions/test/fixture/merge-if-with-else.js

@@ -0,0 +1,4 @@
+if (!matchFn)
+    fix(from, to, path);
+else if (matchFn(options))
+    fix(from, to, path);