Force new line if the whitespace between comments doesn't have a line break

Tweeking KEEP_FIRST_COLUMN_COMMENT setting and one-line comments generated on the same line.

 #KT-4175 In Progress

idea/src/org/jetbrains/kotlin/idea/formatter/kotlinSpacingRules.kt

@@ -21,6 +21,7 @@ import com.intellij.formatting.Spacing
 import com.intellij.formatting.SpacingBuilder
 import com.intellij.formatting.SpacingBuilder.RuleBuilder
 import com.intellij.lang.ASTNode
+import com.intellij.psi.PsiWhiteSpace
 import com.intellij.psi.codeStyle.CodeStyleSettings
 import com.intellij.psi.formatter.FormatterUtil
 import com.intellij.psi.tree.IElementType
@@ -289,6 +290,17 @@ fun createSpacingBuilder(settings: CodeStyleSettings): KotlinSpacingBuilder {
             }
 
             if (kotlinCommonSettings.KEEP_FIRST_COLUMN_COMMENT) {
+                inPosition(parent = null, left = EOL_COMMENT, right = EOL_COMMENT).customRule { parent, left, right ->
+                    val nodeBeforeRight = right.node.treePrev
+                    if (nodeBeforeRight is PsiWhiteSpace && !nodeBeforeRight.textContains('\n')) {
+                        // Several line comments happened to be generated in one line
+                        Spacing.createSpacing(1, 0, 1, settings.KEEP_LINE_BREAKS, settings.KEEP_BLANK_LINES_IN_CODE)
+                    }
+                    else {
+                        null
+                    }
+                }
+
                 inPosition(rightSet = TokenSet.create(EOL_COMMENT, BLOCK_COMMENT)).spacing(
                         Spacing.createKeepingFirstColumnSpacing(0, Integer.MAX_VALUE, settings.KEEP_LINE_BREAKS, kotlinCommonSettings.KEEP_BLANK_LINES_IN_CODE))
             }