Fix formatOnEnter for double newlines

src/harness/fourslash.ts

@@ -1486,6 +1486,12 @@ namespace FourSlash {
             this.fixCaretPosition();
         }
 
+        public formatOnType(pos: number, key: string) {
+            const edits = this.languageService.getFormattingEditsAfterKeystroke(this.activeFile.fileName, pos, key, this.formatCodeOptions);
+            this.currentCaretPosition += this.applyEdits(this.activeFile.fileName, edits, /*isFormattingEdit*/ true);
+            this.fixCaretPosition();
+        }
+
         private updateMarkersForEdit(fileName: string, minChar: number, limChar: number, text: string) {
             for (let i = 0; i < this.testData.markers.length; i++) {
                 const marker = this.testData.markers[i];
@@ -3223,6 +3229,10 @@ namespace FourSlashInterface {
             this.state.formatSelection(this.state.getMarkerByName(startMarker).position, this.state.getMarkerByName(endMarker).position);
         }
 
+        public onType(posMarker: string, key: string) {
+            this.state.formatOnType(this.state.getMarkerByName(posMarker).position, key);
+        }
+
         public setOption(name: string, value: number): void;
         public setOption(name: string, value: string): void;
         public setOption(name: string, value: boolean): void;

src/services/formatting/formatting.ts

@@ -81,6 +81,12 @@ namespace ts.formatting {
         while (isWhiteSpace(sourceFile.text.charCodeAt(endOfFormatSpan)) && !isLineBreak(sourceFile.text.charCodeAt(endOfFormatSpan))) {
             endOfFormatSpan--;
         }
+        // if the character at the end of the span is a line break, we shouldn't include it, because it indicates we don't want to
+        // touch the current line at all. Also, on some OSes the line break consists of two characters (\r\n), we should test if the
+        // previous character before the end of format span is line break character as well.
+        while (isLineBreak(sourceFile.text.charCodeAt(endOfFormatSpan))) {
+            endOfFormatSpan--;
+        }
         const span = {
             // get start position for the previous line
             pos: getStartPositionOfLine(line - 1, sourceFile),

tests/cases/fourslash/formatOnEnter.ts

@@ -0,0 +1,17 @@
+/// <reference path="fourslash.ts"/>
+
+/////*3*/function listAPIFiles (path : string): string[] {
+////    /*1*/
+////    /*2*/
+////}
+
+goTo.marker("1");
+format.onType("1", "\n");
+verify.currentLineContentIs("    ");
+
+goTo.marker("2");
+format.onType("2", "\n");
+verify.currentLineContentIs("    ");
+
+goTo.marker("3");
+verify.currentLineContentIs("function listAPIFiles(path: string): string[] {");

tests/cases/fourslash/fourslash.ts

@@ -246,6 +246,7 @@ declare namespace FourSlashInterface {
         copyFormatOptions(): FormatCodeOptions;
         setFormatOptions(options: FormatCodeOptions): any;
         selection(startMarker: string, endMarker: string): void;
+        onType(posMarker: string, key: string): void;
         setOption(name: string, value: number): any;
         setOption(name: string, value: string): any;
         setOption(name: string, value: boolean): any;