Merge branch 'scope-input-errors' into 'master'

Stop injecting field errors where they won't be used.

## What does this MR do?

Filters the form elements which gl_field_errors validates, excluding input types button, submit and checkbox.

## Why was this MR needed?

This won't make a difference in UX, but I just noticed that we are currently validating and injecting errors into the DOM for all non-hidden inputs. Doing so is unnecessary, and could introduce performance problems on forms with larger numbers of inputs.

## Does this MR meet the acceptance criteria?

- [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !6929

app/assets/javascripts/gl_field_errors.js.es6

@@ -137,8 +137,11 @@
     }
 
     initValidators () {
-      // select all non-hidden inputs in form
-      this.state.inputs = this.form.find(':input:not([type=hidden])').toArray()
+      // register selectors here as needed
+      const validateSelectors = [':text', ':password', '[type=email]']
+        .map((selector) => `input${selector}`).join(',');
+
+      this.state.inputs = this.form.find(validateSelectors).toArray()
         .filter((input) => !input.classList.contains(customValidationFlag))
         .map((input) => new GlFieldError({ input, formErrors: this }));
 

spec/javascripts/gl_field_errors_spec.js.es6

@@ -11,12 +11,12 @@
       this.fieldErrors = new global.GlFieldErrors($form);
     });
 
-    it('should properly initialize the form', function() {
+    it('should select the correct input elements', function() {
       expect(this.$form).toBeDefined();
       expect(this.$form.length).toBe(1);
       expect(this.fieldErrors).toBeDefined();
       const inputs = this.fieldErrors.state.inputs;
-      expect(inputs.length).toBe(5);
+      expect(inputs.length).toBe(4);
     });
 
     it('should ignore elements with custom error handling', function() {