Fix tab-to-tab-stop for offside-rule languages

src/commands/tab.ts

@@ -2,10 +2,60 @@ import * as vscode from "vscode";
 import { Selection, TextEditor } from "vscode";
 import { makeParallel, EmacsCommand } from ".";
 
+const offsideRuleLanguageIds = ["python"];
+
 export class TabToTabStop extends EmacsCommand {
   public readonly id = "tabToTabStop";
 
   public run(textEditor: TextEditor, isInMarkMode: boolean, prefixArgument: number | undefined): Thenable<unknown> {
+    if (offsideRuleLanguageIds.includes(textEditor.document.languageId)) {
+      const tabSize = textEditor.options.tabSize as number;
+      const insertSpaces = textEditor.options.insertSpaces as boolean;
+
+      const indentChars = insertSpaces ? tabSize : 1;
+
+      const editsAndMoves = textEditor.selections.map((selection) => {
+        let prevNonEmptyLine: vscode.TextLine | undefined;
+        for (let i = selection.active.line - 1; i >= 0; i--) {
+          const line = textEditor.document.lineAt(i);
+          if (line.isEmptyOrWhitespace) {
+            continue;
+          }
+          prevNonEmptyLine = line;
+          break;
+        }
+        const prevIndentHeadChar = prevNonEmptyLine?.firstNonWhitespaceCharacterIndex ?? 0;
+        const newIndentUnits = Math.floor(prevIndentHeadChar / tabSize) + 1;
+        const newIndentChars = newIndentUnits * indentChars;
+
+        const curLine = textEditor.document.lineAt(selection.active.line);
+        const charsToInsert = Math.max(newIndentChars - curLine.firstNonWhitespaceCharacterIndex, 0);
+        const charsToMoveCurAfterIndent = Math.max(
+          selection.active.character - curLine.firstNonWhitespaceCharacterIndex,
+          0,
+        );
+
+        return {
+          line: selection.active.line,
+          charsToInsert,
+          cursorChars: newIndentChars + charsToMoveCurAfterIndent,
+        };
+      });
+
+      const indentChar = insertSpaces ? " " : "\t";
+      textEditor.edit((editBuilder) => {
+        editsAndMoves.forEach((editAndMove) => {
+          const lineHead = new vscode.Position(editAndMove.line, 0);
+          editBuilder.insert(lineHead, indentChar.repeat(editAndMove.charsToInsert));
+        });
+      });
+      textEditor.selections = editsAndMoves.map((editAndMove) => {
+        const active = new vscode.Position(editAndMove.line, editAndMove.cursorChars);
+        return new vscode.Selection(active, active);
+      });
+      this.emacsController.exitMarkMode();
+    }
+
     // A single call of `editor.action.reindentselectedlines`
     // only affects a first selection which has a not indented line.
     // So we need to call it as many times as the number of selections.
@@ -20,6 +70,7 @@ export class TabToTabStop extends EmacsCommand {
         const indentHeadPos = new vscode.Position(selection.active.line, indentHeadChar);
         return new Selection(indentHeadPos, indentHeadPos);
       });
+      this.emacsController.exitMarkMode();
     });
   }
 }