Fix unused variables sharing names of imports

If you have code that looks something like the following:

```js
import uuid from 'uuid';

function bar() {
  return uuid.v4();
}

export default function foo() {
  const things = {
    uuid: bar(),
    henric: 'is cool',
  };

  const { uuid, henric } = things;
  return henric;
}
```

Running fix imports will toggle between adding and removing the `uuid`
import. This is because the error that eslint reports relates to the
`uuid` defined by `const { uuid, henric } = things;` line. However,
after it is removed, we get a second error saying that it is used but
never defined (by `return uuid.v4()`), so it gets added back again.

To fix this, I added some logic that verifies that the eslint error for
unused variables happens within the imports block.

While I was working on the fix_imports method, I found a couple of
opportunities to return early to avoid doing unnecessary work.

Fixes #203

lib/import_js/importer.rb

@@ -55,6 +55,10 @@ def goto
     end
 
     REGEX_ESLINT_RESULT = /
+      :
+      (?<line>\d+)                # <line> line number
+      :\d+:
+      \s
       (?<quote>["'])              # <quote> opening quote
       (?<variable_name>[^\1]+)    # <variable_name>
       \k<quote>
@@ -73,22 +77,34 @@ def fix_imports
       reload_config
       eslint_result = run_eslint_command
 
-      unused_variables = Set.new
+      return if eslint_result.empty?
+
+      unused_variables = {}
       undefined_variables = Set.new
 
       eslint_result.each do |line|
         match = REGEX_ESLINT_RESULT.match(line)
         next unless match
         if match[:type] == 'is defined but never used'
-          unused_variables.add match[:variable_name]
+          unused_variables[match[:variable_name]] ||= Set.new
+          unused_variables[match[:variable_name]].add match[:line].to_i
         else
           undefined_variables.add match[:variable_name]
         end
       end
 
+      return if unused_variables.empty? && undefined_variables.empty?
+
       old_imports = find_current_imports
+
+      # Filter out unused variables that do not appear within the imports block.
+      unused_variables.select! do |_, line_numbers|
+        any_line_numbers_within_imports_range?(
+          line_numbers, old_imports[:range])
+      end
+
       new_imports = old_imports[:imports].clone
-      new_imports.delete_variables!(unused_variables.to_a)
+      new_imports.delete_variables!(unused_variables.keys)
 
       undefined_variables.each do |variable|
         js_module = find_one_js_module(variable)
@@ -130,6 +146,19 @@ def message(str)
       @editor.message("ImportJS: #{str}")
     end
 
+    # @param line_numbers [Set]
+    # @param imports_range [Range]
+    # @return [Boolean]
+    def any_line_numbers_within_imports_range?(line_numbers, imports_range)
+      line_numbers.each do |line_number|
+        # Because the range uses line indexes, which are 0-based, and
+        # line_numbers are 1-based, we need to adjust one of them to make this
+        # comparison properly.
+        return true if imports_range.include?(line_number - 1)
+      end
+      false
+    end
+
     ESLINT_STDOUT_ERROR_REGEXES = [
       /Parsing error: /,
       /Unrecoverable syntax error/,

spec/import_js/importer_spec.rb

@@ -2151,7 +2151,7 @@ def self.current_selection=(index)
 bar
       EOS
       let(:eslint_result) do
-        'stdin:1:4: "foo" is defined but never used [Error/no-unused-vars]'
+        'stdin:2:7: "foo" is defined but never used [Error/no-unused-vars]'
       end
 
       it 'removes that import' do
@@ -2216,7 +2216,7 @@ def self.current_selection=(index)
       EOS
 
       let(:eslint_result) do
-        'stdin:3:11: "bar" is defined but never used ' \
+        'stdin:1:11: "bar" is defined but never used ' \
         "[Error/no-unused-vars]\n" \
         'stdin:3:11: "foo" is not defined. [Error/no-undef]'
       end
@@ -2238,7 +2238,7 @@ def self.current_selection=(index)
       EOS
 
       let(:eslint_result) do
-        'stdin:3:11: "foo" is defined but never used ' \
+        'stdin:1:11: "foo" is defined but never used ' \
         "[Error/no-unused-vars]\n" \
       end
 
@@ -2260,7 +2260,7 @@ def self.current_selection=(index)
       EOS
 
       let(:eslint_result) do
-        'stdin:3:11: "foo" is defined but never used ' \
+        'stdin:2:11: "foo" is defined but never used ' \
         "[Error/no-unused-vars]\n" \
       end
 
@@ -2272,6 +2272,33 @@ def self.current_selection=(index)
         EOS
       end
     end
+
+    context 'when an unused variable that shares its name with an import exists' do
+      let(:text) { <<-EOS.strip }
+import uuid from 'uuid';
+
+function bar() {
+  return uuid.v4();
+}
+
+export default function foo() {
+  const things = {
+    uuid: bar(),
+    henric: 'is cool',
+  };
+
+  const { uuid, henric } = things;
+  return henric;
+}
+      EOS
+      let(:eslint_result) do
+        'stdin:13:11: "uuid" is defined but never used [Error/no-unused-vars]'
+      end
+
+      it 'does not remove the import' do
+        expect(subject).to eq(text)
+      end
+    end
   end
 
   describe '#rewrite_imports' do