no-duplicates: Add autofix

docs/rules/no-duplicates.md

@@ -1,6 +1,7 @@
 # import/no-duplicates
 
 Reports if a resolved path is imported more than once.
++(fixable) The `--fix` option on the [command line] automatically fixes some problems reported by this rule.
 
 ESLint core has a similar rule ([`no-duplicate-imports`](http://eslint.org/docs/rules/no-duplicate-imports)), but this version
 is different in two key ways:

src/rules/no-duplicates.js

@@ -2,21 +2,193 @@ import resolve from 'eslint-module-utils/resolve'
 import docsUrl from '../docsUrl'
 
 function checkImports(imported, context) {
-  for (let [module, nodes] of imported.entries()) {
-    if (nodes.size > 1) {
-      for (let node of nodes) {
-        context.report(node, `'${module}' imported multiple times.`)
+  for (const [module, nodes] of imported.entries()) {
+    if (nodes.length > 1) {
+      const message = `'${module}' imported multiple times.`
+      const [first, ...rest] = nodes
+      const sourceCode = context.getSourceCode()
+      const fix = getFix(first, rest, sourceCode)
+
+      context.report({
+        node: first.source,
+        message,
+        fix, // Attach the autofix (if any) to the first import.
+      })
+
+      for (const node of rest) {
+        context.report({
+          node: node.source,
+          message,
+        })
+      }
+    }
+  }
+}
+
+function getFix(first, rest, sourceCode) {
+  const defaultImportNames = new Set(
+    [first, ...rest].map(getDefaultImportName).filter(Boolean)
+  )
+
+  // Bail if there are multiple different default import names – it's up to the
+  // user to choose which one to keep.
+  if (defaultImportNames.size > 1) {
+    return undefined
+  }
+
+  // It's not obvious what the user wants to do with comments associated with
+  // duplicate imports, so skip imports with comments when autofixing.
+  const restWithoutComments = rest.filter(node => !(
+      hasCommentBefore(node, sourceCode) ||
+      hasCommentAfter(node, sourceCode) ||
+      hasCommentInsideNonSpecifiers(node, sourceCode)
+  ))
+
+  const specifiers = restWithoutComments
+    .map(node => {
+      const tokens = sourceCode.getTokens(node)
+      const openBrace = tokens.find(token => isPunctuator(token, '{'))
+      const closeBrace = tokens.find(token => isPunctuator(token, '}'))
+
+      if (openBrace == null || closeBrace == null) {
+        return undefined
+      }
+
+      return {
+        importNode: node,
+        text: sourceCode.text.slice(openBrace.range[1], closeBrace.range[0]),
+        hasTrailingComma: isPunctuator(sourceCode.getTokenBefore(closeBrace), ','),
+        isEmpty: !hasSpecifiers(node),
+      }
+    })
+    .filter(Boolean)
+
+  const unnecessaryImports = restWithoutComments.filter(node =>
+    !hasSpecifiers(node) &&
+    !specifiers.some(specifier => specifier.importNode === node)
+  )
+
+  const shouldAddDefault = getDefaultImportName(first) == null && defaultImportNames.size === 1
+  const shouldAddSpecifiers = specifiers.length > 0
+  const shouldRemoveUnnecessary = unnecessaryImports.length > 0
+
+  if (!(shouldAddDefault || shouldAddSpecifiers || shouldRemoveUnnecessary)) {
+    return undefined
+  }
+
+  return function* (fixer) {
+    const tokens = sourceCode.getTokens(first)
+    const openBrace = tokens.find(token => isPunctuator(token, '{'))
+    const closeBrace = tokens.find(token => isPunctuator(token, '}'))
+    const firstToken = sourceCode.getFirstToken(first)
+    const [defaultImportName] = defaultImportNames
+
+    const firstHasTrailingComma =
+      closeBrace != null &&
+      isPunctuator(sourceCode.getTokenBefore(closeBrace), ',')
+    const firstIsEmpty = !hasSpecifiers(first)
+
+    const [specifiersText] = specifiers.reduce(
+      ([result, needsComma], specifier) => {
+        return [
+          needsComma && !specifier.isEmpty
+            ? `${result},${specifier.text}`
+            : `${result}${specifier.text}`,
+          specifier.isEmpty ? needsComma : true,
+        ]
+      },
+      ['', !firstHasTrailingComma && !firstIsEmpty]
+    )
+
+    if (shouldAddDefault && openBrace == null && shouldAddSpecifiers) {
+      // `import './foo'` → `import def, {...} from './foo'`
+      yield fixer.insertTextAfter(firstToken, ` ${defaultImportName}, {${specifiersText}} from`)
+    } else if (shouldAddDefault && openBrace == null && !shouldAddSpecifiers) {
+      // `import './foo'` → `import def from './foo'`
+      yield fixer.insertTextAfter(firstToken, ` ${defaultImportName} from`)
+    } else if (shouldAddDefault && openBrace != null && closeBrace != null) {
+      // `import {...} from './foo'` → `import def, {...} from './foo'`
+      yield fixer.insertTextAfter(firstToken, ` ${defaultImportName},`)
+      if (shouldAddSpecifiers) {
+        // `import def, {...} from './foo'` → `import def, {..., ...} from './foo'`
+        yield fixer.insertTextBefore(closeBrace, specifiersText)
       }
+    } else if (!shouldAddDefault && openBrace == null && shouldAddSpecifiers) {
+      // `import './foo'` → `import {...} from './foo'`
+      yield fixer.insertTextAfter(firstToken, ` {${specifiersText}} from`)
+    } else if (!shouldAddDefault && openBrace != null && closeBrace != null) {
+      // `import {...} './foo'` → `import {..., ...} from './foo'`
+      yield fixer.insertTextBefore(closeBrace, specifiersText)
+    }
+
+    // Remove imports whose specifiers have been moved into the first import.
+    for (const specifier of specifiers) {
+      yield fixer.remove(specifier.importNode)
+    }
+
+    // Remove imports whose default import has been moved to the first import,
+    // and side-effect-only imports that are unnecessary due to the first
+    // import.
+    for (const node of unnecessaryImports) {
+      yield fixer.remove(node)
     }
   }
 }
 
+function isPunctuator(node, value) {
+  return node.type === 'Punctuator' && node.value === value
+}
+
+// Get the name of the default import of `node`, if any.
+function getDefaultImportName(node) {
+  const defaultSpecifier = node.specifiers
+    .find(specifier => specifier.type === 'ImportDefaultSpecifier')
+  return defaultSpecifier != null ? defaultSpecifier.local.name : undefined
+}
+
+// Checks whether `node` has any non-default specifiers.
+function hasSpecifiers(node) {
+  const specifiers = node.specifiers
+    .filter(specifier => specifier.type === 'ImportSpecifier')
+  return specifiers.length > 0
+}
+
+// Checks whether `node` has a comment (that ends) on the previous line or on
+// the same line as `node` (starts).
+function hasCommentBefore(node, sourceCode) {
+  return sourceCode.getCommentsBefore(node)
+    .some(comment => comment.loc.end.line >= node.loc.start.line - 1)
+}
+
+// Checks whether `node` has a comment (that starts) on the same line as `node`
+// (ends).
+function hasCommentAfter(node, sourceCode) {
+  return sourceCode.getCommentsAfter(node)
+    .some(comment => comment.loc.start.line === node.loc.end.line)
+}
+
+// Checks whether `node` has any comments _inside,_ except inside the `{...}`
+// part (if any).
+function hasCommentInsideNonSpecifiers(node, sourceCode) {
+  const tokens = sourceCode.getTokens(node)
+  const openBraceIndex = tokens.findIndex(token => isPunctuator(token, '{'))
+  const closeBraceIndex = tokens.findIndex(token => isPunctuator(token, '}'))
+  // Slice away the first token, since we're no looking for comments _before_
+  // `node` (only inside). If there's a `{...}` part, look for comments before
+  // the `{`, but not before the `}` (hence the `+1`s).
+  const someTokens = openBraceIndex >= 0 && closeBraceIndex >= 0
+    ? tokens.slice(1, openBraceIndex + 1).concat(tokens.slice(closeBraceIndex + 1))
+    : tokens.slice(1)
+  return someTokens.some(token => sourceCode.getCommentsBefore(token).length > 0)
+}
+
 module.exports = {
   meta: {
     type: 'problem',
     docs: {
       url: docsUrl('no-duplicates'),
     },
+    fixable: 'code',
   },
 
   create: function (context) {
@@ -29,9 +201,9 @@ module.exports = {
         const importMap = n.importKind === 'type' ? typesImported : imported
 
         if (importMap.has(resolvedPath)) {
-          importMap.get(resolvedPath).add(n.source)
+          importMap.get(resolvedPath).push(n)
         } else {
-          importMap.set(resolvedPath, new Set([n.source]))
+          importMap.set(resolvedPath, [n])
         }
       },