feat(to-ternary): new command

src/commands/index.ts

@@ -13,6 +13,7 @@ import { noShorthand } from './no-shorthand'
 import { noType } from './no-type'
 import { keepUnique } from './keep-unique'
 import { regex101 } from './regex101'
+import { toTernary } from './to-ternary'
 
 // @keep-sorted
 export {
@@ -31,6 +32,7 @@ export {
   toPromiseAll,
   toStringLiteral,
   toTemplateLiteral,
+  toTernary,
 }
 
 // @keep-sorted
@@ -50,4 +52,5 @@ export const builtinCommands = [
   toPromiseAll,
   toStringLiteral,
   toTemplateLiteral,
+  toTernary,
 ]

src/commands/to-ternary.md

@@ -0,0 +1,37 @@
+# `to-ternary`
+
+Convert an `if-else` statement to a [`ternary expression`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Conditional_operator).
+
+## Triggers
+
+- `/// to-ternary`
+- `/// to-3`
+- `/// 2ternary`
+- `/// 23`
+
+## Examples
+
+```js
+/// to-ternary
+if (condition)
+  foo()
+else
+  bar = 1
+
+// For conditional assignments to the same variable
+/// to-ternary
+if (condition1)
+  foo = 1
+else if (condition2)
+  foo = bar
+else
+  foo = baz()
+```
+
+Will be converted to (the command comment will be removed along the way):
+
+```js
+condition ? foo() : bar = 1
+
+foo = condition1 ? 1 : condition2 ? bar : baz()
+```

src/commands/to-ternary.test.ts

@@ -0,0 +1,96 @@
+import { toTernary as command } from './to-ternary'
+import { $, run } from './_test-utils'
+
+run(
+  command,
+  // no `else`
+  {
+    code: $`
+      /// to-ternary
+      if (c1)
+        foo()
+      else if (c2)
+        bar = 1
+    `,
+    errors: ['command-error'],
+  },
+  // too many lines in a `if`
+  {
+    code: $`
+      /// 2ternary
+      if (c1) {
+        foo()
+        bar = 1
+      }
+      else {
+        bar = 2
+      }
+    `,
+    errors: ['command-error'],
+  },
+  // normal
+  {
+    code: $`
+      /// to-3
+      if (c1)
+        foo()
+      else
+        bar = 1
+    `,
+    output: $`
+      c1 ? foo() : bar = 1
+    `,
+    errors: ['command-fix'],
+  },
+  // more `else-if` and block
+  {
+    code: $`
+      /// 23
+      if (a > b) {
+        foo()
+      }
+      else if (c2) {
+        bar = 1
+      }
+      else {
+        baz()
+      }
+    `,
+    output: $`
+      a > b ? foo() : c2 ? bar = 1 : baz()
+    `,
+    errors: ['command-fix'],
+  },
+  // same name assignment
+  {
+    code: $`
+      /// to-ternary
+      if (c1)
+        foo = 1
+      else if (c2)
+        foo = bar
+      else
+        foo = baz()
+    `,
+    output: $`
+      foo = c1 ? 1 : c2 ? bar : baz()
+    `,
+    errors: ['command-fix'],
+  },
+  // different names assignment
+  {
+    code: $`
+      /// to-ternary
+      if (c1)
+        foo = 1
+      else if (c2)
+        bar = 2
+      else
+        baz()
+    `,
+    output: $`
+      c1 ? foo = 1 : c2 ? bar = 2 : baz()
+    `,
+    errors: ['command-fix'],
+  },
+)

src/commands/to-ternary.ts

@@ -0,0 +1,74 @@
+import type { Command, Tree } from '../types'
+
+export const toTernary: Command = {
+  name: 'to-ternary',
+  match: /^\s*[/:@]\s*(?:to-|2)(?:ternary|3)$/,
+  action(ctx) {
+    const node = ctx.findNodeBelow('IfStatement')
+
+    if (!node)
+      return ctx.reportError('Unable to find an `if` statement to convert')
+
+    let result = ''
+    let isAssignment = true
+
+    const normalizeStatement = (n: Tree.Statement | null) => {
+      if (!n)
+        return ctx.reportError('Unable to convert `if` statement without an `else` clause')
+      if (n.type === 'BlockStatement') {
+        if (n.body.length !== 1)
+          return ctx.reportError('Unable to convert statement contains more than one expression')
+        else return n.body[0]
+      }
+      else {
+        return n
+      }
+    }
+
+    const getAssignmentId = (n: Tree.Statement) => {
+      if (n.type === 'IfStatement')
+        n = n.consequent
+      if (n.type !== 'ExpressionStatement' || n.expression.type !== 'AssignmentExpression' || n.expression.left.type !== 'Identifier')
+        return
+      return ctx.getTextOf(n.expression.left)
+    }
+
+    let ifNode: Tree.IfStatement = node
+    while (ifNode) {
+      const consequent = normalizeStatement(ifNode.consequent)
+      const alternate = normalizeStatement(ifNode.alternate)
+
+      if (!consequent || !alternate)
+        return
+
+      if (isAssignment) {
+        const ifId = getAssignmentId(consequent)
+        const elseId = getAssignmentId(alternate)
+
+        if (!ifId || ifId !== elseId)
+          isAssignment = false
+      }
+
+      result += `${ctx.getTextOf(ifNode.test)} ? ${ctx.getTextOf(consequent)} : `
+
+      if (alternate.type !== 'IfStatement') {
+        result += ctx.getTextOf(alternate)
+        break
+      }
+      else {
+        ifNode = alternate
+      }
+    }
+
+    if (isAssignment) {
+      const id = getAssignmentId(normalizeStatement(node.consequent)!)
+      result = `${id} = ${result.replaceAll(`${id} = `, '')}`
+    }
+
+    ctx.report({
+      node,
+      message: 'Convert to ternary',
+      fix: fix => fix.replaceTextRange(node.range, result),
+    })
+  },
+}