FIX: Format selection as multiline code only when selection spans multiple lines.

app/assets/javascripts/discourse/components/d-editor.js.es6

@@ -364,12 +364,12 @@ export default Ember.Component.extend({
     });
   },
 
-  _getSelected(trimLeading) {
+  _getSelected(trimLeading, opts) {
     if (!this.get('ready')) { return; }
 
     const textarea = this.$('textarea.d-editor-input')[0];
     const value = textarea.value;
-    var start = textarea.selectionStart;
+    let start = textarea.selectionStart;
     let end = textarea.selectionEnd;
 
     // trim trailing spaces cause **test ** would be invalid
@@ -388,7 +388,12 @@ export default Ember.Component.extend({
     const pre = value.slice(0, start);
     const post = value.slice(end);
 
-    return { start, end, value: selVal, pre, post };
+    if (opts && opts.lineVal) {
+      const lineVal = value.split("\n")[value.substr(0, textarea.selectionStart).split("\n").length - 1];
+      return { start, end, value: selVal, pre, post, lineVal };
+    } else {
+      return { start, end, value: selVal, pre, post };
+    }
   },
 
   _selectText(from, length) {
@@ -535,21 +540,31 @@ export default Ember.Component.extend({
     },
 
     formatCode() {
-      const sel = this._getSelected();
-      const hasNewLine = sel.value.indexOf("\n") !== -1;
+      const sel = this._getSelected('', { lineVal: true });
+      const selValue = sel.value;
+      const hasNewLine = selValue.indexOf("\n") !== -1;
+      const isBlankLine = sel.lineVal.trim().length === 0;
+      const isFourSpacesIndent = this.siteSettings.code_formatting_style === FOUR_SPACES_INDENT;
 
-      if (this.siteSettings.code_formatting_style === FOUR_SPACES_INDENT) {
-        return (hasNewLine ?
-                this._applySurround(sel, '    ', '', 'code_text') :
-                this._applySurround(sel, '`', '`', 'code_text'));
-      } else {
-        const preNewline = (sel.pre[-1] !== "\n" && sel.pre !== "") ? "\n" : "";
-        const postNewline = sel.post[0] !== "\n" ? "\n" : "";
-
-        if (hasNewLine) {
-          return this._addText(sel, `${preNewline}\`\`\`\n${sel.value}\n\`\`\`${postNewline}`);
+      if (!hasNewLine) {
+        if (selValue.length === 0 && isBlankLine) {
+          if (isFourSpacesIndent) {
+            const example = I18n.t(`composer.code_text`);
+            this.set('value', `${sel.pre}    ${example}${sel.post}`);
+            return this._selectText(sel.pre.length + 4, example.length);
+          } else {
+            return this._applySurround(sel, "```\n", "\n```", 'paste_code_text');
+          }
         } else {
-          return this._applySurround(sel, `${preNewline}\`\`\`\n`, `\n\`\`\`${postNewline}`, 'paste_code_text');
+          return this._applySurround(sel, '`', '`', 'code_title');
+        }
+      } else {
+        if (isFourSpacesIndent) {
+          return this._applySurround(sel, '    ', '', 'code_text');
+        } else {
+          const preNewline = (sel.pre[-1] !== "\n" && sel.pre !== "") ? "\n" : "";
+          const postNewline = sel.post[0] !== "\n" ? "\n" : "";
+          return this._addText(sel, `${preNewline}\`\`\`\n${sel.value}\n\`\`\`${postNewline}`);
         }
       }
     },

test/javascripts/components/d-editor-test.js.es6

@@ -293,7 +293,6 @@ componentTest('code button', {
   template: '{{d-editor value=value}}',
   setup() {
     this.siteSettings.code_formatting_style = '4-spaces-indent';
-    this.set('value', "first line\n\nsecond line\n\nthird line");
   },
 
   test(assert) {
@@ -301,7 +300,56 @@ componentTest('code button', {
 
     click('button.code');
     andThen(() => {
-      assert.equal(this.get('value'), "first line\n\nsecond line\n\nthird line`" + I18n.t('composer.code_text') + "`");
+      assert.equal(this.get('value'),
+`    ${I18n.t('composer.code_text')}`
+      );
+
+      this.set('value', "first line\n\nsecond line\n\nthird line");
+
+      textarea.selectionStart = 11;
+      textarea.selectionEnd = 11;
+    });
+
+    click('button.code');
+    andThen(() => {
+      assert.equal(this.get('value'),
+`first line
+    ${I18n.t('composer.code_text')}
+second line
+
+third line`
+      );
+
+      this.set('value', "first line\n\nsecond line\n\nthird line");
+    });
+
+
+    click('button.code');
+    andThen(() => {
+      assert.equal(this.get('value'),
+`first line
+
+second line
+
+third line\`${I18n.t('composer.code_title')}\``
+      );
+      this.set('value', "first line\n\nsecond line\n\nthird line");
+    });
+
+    andThen(() => {
+      textarea.selectionStart = 5;
+      textarea.selectionEnd = 5;
+    });
+
+    click('button.code');
+    andThen(() => {
+      assert.equal(this.get('value'),
+`first\`${I18n.t('composer.code_title')}\` line
+
+second line
+
+third line`
+      );
       this.set('value', "first line\n\nsecond line\n\nthird line");
     });
 
@@ -357,8 +405,7 @@ componentTest('code fences', {
       assert.equal(this.get('value'),
 `\`\`\`
 ${I18n.t("composer.paste_code_text")}
-\`\`\`
-`
+\`\`\``
       );
 
       assert.equal(textarea.selectionStart, 4);
@@ -393,16 +440,13 @@ third line
     click('button.code');
     andThen(() => {
       assert.equal(this.get('value'),
-`\`\`\`
-${I18n.t('composer.paste_code_text')}
-\`\`\`
-first line
+`\`${I18n.t('composer.code_title')}\`first line
 second line
 third line`
       );
 
-      assert.equal(textarea.selectionStart, 4);
-      assert.equal(textarea.selectionEnd, 27);
+      assert.equal(textarea.selectionStart, 1);
+      assert.equal(textarea.selectionEnd, I18n.t('composer.code_title').length + 1);
 
       this.set('value', 'first line\nsecond line\nthird line');
 
@@ -413,15 +457,13 @@ third line`
     click('button.code');
     andThen(() => {
       assert.equal(this.get('value'),
-`\`\`\`
-first line
-\`\`\`
+`\`first line\`
 second line
 third line`
       );
 
-      assert.equal(textarea.selectionStart, 4);
-      assert.equal(textarea.selectionEnd, 14);
+      assert.equal(textarea.selectionStart, 1);
+      assert.equal(textarea.selectionEnd, 11);
 
       this.set('value', 'first line\nsecond line\nthird line');