Add editor.indentSize option

This is an attempt to address issue #10339.

Background:

Currently, the `editor.tabSize` option does two things - it specifies the width of the tab character and it specifies how many columns to advance when the tab key is pressed. However, there is code in the wild that has a mix of spaces and tabs that expects these two values to be different.

These generally use and indent size of 2 or 4 and spaces are used for indentation until the indent becomes >= 8. The tab character size is excpected to be 8 and groups of 8 spaces are replaced with a tab character. Indent levels end up looking like 2 spaces, 4 spaces, 6 spaces, 1 tab, 1 tab + 2 spaces, and so on.

Implementation:

In the editor options, a new option, `editor.indentSize` is added. This, in conjunction with `editor.tabSize` has the same semantics as `indent_size` and `tab_width` in the well known [EditorConfig specification][1].

> indent_size: a whole number defining the number of columns used for each indentation level and the width of soft tabs (when supported). When set to "tab", the value of tab_width (if specified) will be used.
>
> tab_width: a whole number defining the number of columns used to represent a tab character. This defaults to the value of indent_size and doesn't usually need to be specified.

[1]: editorconfig.org

The new `indentSize` option takes a numeric value or "tab" just as EditorConfig's `indent_size`. The default value is set to "tab" so that current default behavior of VS Code does not change and existing user settings will not break.

When getting the new `indentSize` option programatically, it always returns a numeric value (just as `tabSize` does when set to the deprecated "auto" value).

In the text editor model, a new property is added for `indentSize`. Unlike the configuration options where the value of one property influences the other, In this code `tabSize` now should only mean "the width of the tab character" and `indentSize` should only mean "how may columns is one indent".

The cursor operations and shift command are updated to reflect these new semantics.

src/vs/workbench/api/node/extHost.protocol.ts

@@ -176,6 +176,7 @@ export interface MainThreadDocumentsShape extends IDisposable {
 
 export interface ITextEditorConfigurationUpdate {
 	tabSize?: number | 'auto';
+	indentSize?: number | 'tab';
 	insertSpaces?: boolean | 'auto';
 	cursorStyle?: TextEditorCursorStyle;
 	lineNumbers?: TextEditorLineNumbersStyle;
@@ -183,6 +184,7 @@ export interface ITextEditorConfigurationUpdate {
 
 export interface IResolvedTextEditorConfiguration {
 	tabSize: number;
+	indentSize: number;
 	insertSpaces: boolean;
 	cursorStyle: TextEditorCursorStyle;
 	lineNumbers: TextEditorLineNumbersStyle;

src/vs/workbench/api/node/extHostTextEditor.ts

@@ -142,6 +142,7 @@ export class ExtHostTextEditorOptions implements vscode.TextEditorOptions {
 	private _id: string;
 
 	private _tabSize: number;
+	private _indentSize: number;
 	private _insertSpaces: boolean;
 	private _cursorStyle: TextEditorCursorStyle;
 	private _lineNumbers: TextEditorLineNumbersStyle;
@@ -154,6 +155,7 @@ export class ExtHostTextEditorOptions implements vscode.TextEditorOptions {
 
 	public _accept(source: IResolvedTextEditorConfiguration): void {
 		this._tabSize = source.tabSize;
+		this._indentSize = source.indentSize;
 		this._insertSpaces = source.insertSpaces;
 		this._cursorStyle = source.cursorStyle;
 		this._lineNumbers = source.lineNumbers;
@@ -200,6 +202,47 @@ export class ExtHostTextEditorOptions implements vscode.TextEditorOptions {
 		}));
 	}
 
+	public get indentSize(): number | string {
+		return this._indentSize;
+	}
+
+	private _validateIndentSize(value: number | string): number | 'tab' | null {
+		if (value === 'tab') {
+			return 'tab';
+		}
+		if (typeof value === 'number') {
+			let r = Math.floor(value);
+			return (r > 0 ? r : null);
+		}
+		if (typeof value === 'string') {
+			let r = parseInt(value, 10);
+			if (isNaN(r)) {
+				return null;
+			}
+			return (r > 0 ? r : null);
+		}
+		return null;
+	}
+
+	public set indentSize(value: number | string) {
+		let indentSize = this._validateIndentSize(value);
+		if (indentSize === null) {
+			// ignore invalid call
+			return;
+		}
+		if (typeof indentSize === 'number') {
+			if (this._indentSize === indentSize) {
+				// nothing to do
+				return;
+			}
+			// reflect the new indentSize value immediately
+			this._indentSize = indentSize;
+		}
+		warnOnError(this._proxy.$trySetOptions(this._id, {
+			indentSize: indentSize
+		}));
+	}
+
 	public get insertSpaces(): boolean | string {
 		return this._insertSpaces;
 	}
@@ -273,6 +316,19 @@ export class ExtHostTextEditorOptions implements vscode.TextEditorOptions {
 			}
 		}
 
+		if (typeof newOptions.indentSize !== 'undefined') {
+			let indentSize = this._validateIndentSize(newOptions.indentSize);
+			if (indentSize === 'tab') {
+				hasUpdate = true;
+				bulkConfigurationUpdate.indentSize = indentSize;
+			} else if (typeof indentSize === 'number' && this._indentSize !== indentSize) {
+				// reflect the new indentSize value immediately
+				this._indentSize = indentSize;
+				hasUpdate = true;
+				bulkConfigurationUpdate.indentSize = indentSize;
+			}
+		}
+
 		if (typeof newOptions.insertSpaces !== 'undefined') {
 			let insertSpaces = this._validateInsertSpaces(newOptions.insertSpaces);
 			if (insertSpaces === 'auto') {