fix(terminal): keep Windows shell paths intact

The Shell path setting was split with POSIX rules, where a backslash
escapes the next character, so C:\Windows\system32\cmd.exe reached the
backend as C:Windowssystem32cmd.exe and every new terminal failed to
start. On Windows a backslash is now a path separator, and an unquoted
path up to its .exe/.cmd/.bat/.com is the program even with spaces, as
the Installed Shells menu and Browse set it. Paths picked there are
quoted when they contain whitespace.

Fixes #1327

src/features/settings/pages/tools.tsx

@@ -7,6 +7,7 @@
 import { FontPicker } from "../components/FontPicker";
 import { useEffect, useId, useRef, useState, type ReactNode } from "react";
 import clsx from "clsx";
+import { quotePath } from "@/platform/commandLine";
 import { commands, isTauri } from "@/platform/ipc";
 import {
   DEFAULT_EXTERNAL_TOOL,
@@ -110,7 +111,7 @@ function ShellPathRow() {
     const { open: pick } = await import("@tauri-apps/plugin-dialog");
     const picked = await pick({ multiple: false, title: "Shell Path" });
     const path = Array.isArray(picked) ? picked[0] : picked;
-    if (path) set(path);
+    if (path) set(quotePath(path));
   };
   return (
     <Row
@@ -142,7 +143,7 @@ function ShellPathRow() {
         anchor={menuRef}
         placement="bottom-end"
         aria-label="Installed shells"
-        items={shells.map((p) => ({ id: p, label: p, checked: p === value, run: () => set(p) }))}
+        items={shells.map((p) => ({ id: p, label: p, checked: quotePath(p) === value, run: () => set(quotePath(p)) }))}
       />
       <IconButton
         icon="folder-open"

src/features/terminal/session.ts

@@ -16,9 +16,9 @@ import { installTerminalPaste, pasteTerminalClipboard } from "./paste";
 import { ImeCommitGate } from "./imeCommit";
 import { ownTerminalInput } from "./imeInput";
 import { findTerminalLinks, resolvePath, type TerminalLink } from "./links";
-import { splitCommandLine } from "@/platform/commandLine";
+import { parseShellCommand } from "@/platform/commandLine";
 import { useProject } from "@/platform/project";
-import { useRemote } from "@/platform/remote";
+import { hostOs, useRemote } from "@/platform/remote";
 import { usePlatform } from "@/platform/platformInfo";
 import { workflowSettings, type TerminalSettingsValid } from "@/platform/workflowSettings";
 import { editorPrefs } from "@/platform/editorSettings";
@@ -530,7 +530,7 @@ export class TerminalSession {
     };
     try {
       const t = workflowSettings().terminal;
-      const [shellPath, ...shellArgs] = splitCommandLine(t.shellPath);
+      const [shellPath, ...shellArgs] = parseShellCommand(t.shellPath, hostOs() === "windows");
       const shell = custom ? custom.program : shellPath;
       const args = custom ? custom.args : shellArgs;
       const info = await call(

src/platform/commandLine.test.ts

@@ -0,0 +1,54 @@
+import { describe, expect, it } from "vitest";
+import { parseShellCommand, quotePath } from "./commandLine";
+
+describe("parseShellCommand", () => {
+  it("keeps Windows paths as typed", () => {
+    expect(parseShellCommand(String.raw`C:\Windows\system32\cmd.exe`, true)).toEqual([
+      String.raw`C:\Windows\system32\cmd.exe`,
+    ]);
+    expect(parseShellCommand(String.raw`C:\Windows\system32\cmd.exe /k C:\tools\init.bat`, true)).toEqual([
+      String.raw`C:\Windows\system32\cmd.exe`,
+      "/k",
+      String.raw`C:\tools\init.bat`,
+    ]);
+  });
+
+  it("takes an unquoted Windows path with spaces up to its executable", () => {
+    expect(parseShellCommand(String.raw`C:\Program Files\PowerShell\7\pwsh.exe`, true)).toEqual([
+      String.raw`C:\Program Files\PowerShell\7\pwsh.exe`,
+    ]);
+    expect(parseShellCommand(String.raw`C:\Program Files\Git\bin\bash.EXE --login -i`, true)).toEqual([
+      String.raw`C:\Program Files\Git\bin\bash.EXE`,
+      "--login",
+      "-i",
+    ]);
+  });
+
+  it("honours quotes", () => {
+    expect(parseShellCommand(String.raw`"C:\Program Files\Git\bin\bash.exe" --login`, true)).toEqual([
+      String.raw`C:\Program Files\Git\bin\bash.exe`,
+      "--login",
+    ]);
+    expect(parseShellCommand(`/bin/zsh --login`, false)).toEqual(["/bin/zsh", "--login"]);
+    expect(parseShellCommand(`"/Applications/My Shell/bin/fish" -l`, false)).toEqual([
+      "/Applications/My Shell/bin/fish",
+      "-l",
+    ]);
+    expect(parseShellCommand(String.raw`/bin/sh -c a\ b`, false)).toEqual(["/bin/sh", "-c", "a b"]);
+  });
+
+  it("is empty for an empty setting", () => {
+    expect(parseShellCommand("  ", true)).toEqual([]);
+    expect(parseShellCommand("", false)).toEqual([]);
+  });
+});
+
+describe("quotePath", () => {
+  it("quotes only paths with whitespace", () => {
+    expect(quotePath(String.raw`C:\Windows\system32\cmd.exe`)).toBe(String.raw`C:\Windows\system32\cmd.exe`);
+    expect(quotePath(String.raw`C:\Program Files\PowerShell\7\pwsh.exe`)).toBe(
+      String.raw`"C:\Program Files\PowerShell\7\pwsh.exe"`,
+    );
+    expect(parseShellCommand(quotePath("/Applications/My Shell/fish"), false)).toEqual(["/Applications/My Shell/fish"]);
+  });
+});

src/platform/commandLine.ts

@@ -67,6 +67,28 @@ export function parseArgs(input: string, windowsPaths = false): string[] {
   return out;
 }
 
+/**
+ * The program and arguments of a shell command line (Settings › Terminal › Shell path). On
+ * Windows a backslash is a path separator, and an unquoted path up to its `.exe` / `.cmd` /
+ * `.bat` / `.com` is the program even with spaces in it (`C:\Program Files\…\pwsh.exe -NoLogo`).
+ */
+export function parseShellCommand(line: string, windows: boolean): string[] {
+  const text = line.trim();
+  if (windows && !/["']/.test(text)) {
+    const end = /\.(?:exe|cmd|bat|com)(?=\s|$)/i.exec(text);
+    if (end) {
+      const stop = end.index + end[0].length;
+      return [text.slice(0, stop), ...parseArgs(text.slice(stop), true)];
+    }
+  }
+  return parseArgs(text, windows);
+}
+
+/** `path` as one word of a command line: quoted when it has whitespace. */
+export function quotePath(path: string): string {
+  return /\s/.test(path) ? `"${path}"` : path;
+}
+
 /** Inverse of `parseArgs` (quotes only when needed). */
 export function formatArgs(args: readonly string[]): string {
   return args.map((a) => (a === "" ? "''" : /[\s'"\\$`]/.test(a) ? `'${a.replace(/'/g, `'\\''`)}'` : a)).join(" ");