feat: Improve shell detection logic for better reliability (#420)

Enhances the shell detection process by ensuring that
the system's available shell is only detected if no
previous shell is set. This change addresses potential
issues where an undefined shell could lead to errors
in subsequent operations.

Author: xiaojingming

src/utils/__tests__/shell.spec.ts

@@ -157,8 +157,8 @@ describe("Shell Detection Tests", () => {
 			process.env.COMSPEC = "C:\\Windows\\System32\\cmd.exe"
 
 			const result = getShell()
-			// Should return PowerShell 7 if available
-			expect(result).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			// Should return environment variable
+			expect(result).toBe("C:\\Windows\\System32\\cmd.exe")
 		})
 
 		it("uses PowerShell 7 path if source is 'PowerShell' but no explicit path", () => {
@@ -195,8 +195,7 @@ describe("Shell Detection Tests", () => {
 				WSL: { source: "WSL" },
 			})
 			// Note: getShell() now prioritizes system detection over VS Code config
-			// So it will return PowerShell 7 if available
-			expect(getShell()).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			expect(getShell()).toBe("/bin/bash")
 		})
 
 		it("uses WSL bash when profile name includes 'wsl'", () => {
@@ -206,8 +205,7 @@ describe("Shell Detection Tests", () => {
 				"Ubuntu WSL": {},
 			})
 			// Note: getShell() now prioritizes system detection over VS Code config
-			// So it will return PowerShell 7 if available
-			expect(getShell()).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			expect(getShell()).toBe("/bin/bash")
 		})
 
 		it("defaults to cmd.exe if no special profile is matched", () => {
@@ -216,15 +214,15 @@ describe("Shell Detection Tests", () => {
 			mockVsCodeConfig("windows", "CommandPrompt", {
 				CommandPrompt: {},
 			})
-			expect(getShell()).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			expect(getShell()).toBe("C:\\Windows\\System32\\cmd.exe")
 		})
 
 		it("handles undefined profile gracefully", () => {
 			const existsSyncMock = mockExistsSync(POWER_SHELL_WHITELIST)
 			const statSyncMock = mockStatSync(POWER_SHELL_WHITELIST)
 			// Mock a case where defaultProfileName exists but the profile doesn't
 			mockVsCodeConfig("windows", "NonexistentProfile", {})
-			expect(getShell()).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			expect(getShell()).toBe("C:\\Windows\\System32\\cmd.exe")
 		})
 
 		it("respects userInfo() if no VS Code config is available and shell is allowed", () => {
@@ -242,7 +240,7 @@ describe("Shell Detection Tests", () => {
 			vscode.workspace.getConfiguration = () => ({ get: () => undefined }) as any
 			vi.mocked(userInfo).mockReturnValue({ shell: "C:\\Custom\\PowerShell.exe" } as any)
 
-			expect(getShell()).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			expect(getShell()).toBe("C:\\Windows\\System32\\cmd.exe")
 		})
 
 		it("uses COMSPEC environment variable when available", () => {
@@ -278,7 +276,7 @@ describe("Shell Detection Tests", () => {
 
 			// Note: getShell() now prioritizes system detection over VS Code config
 			// So it will return the default shell for the platform
-			expect(getShell()).toBe("/bin/zsh")
+			expect(getShell()).toBe("/usr/local/bin/fish")
 
 			existsSyncMock.mockRestore()
 			statSyncMock.mockRestore()
@@ -306,8 +304,7 @@ describe("Shell Detection Tests", () => {
 
 			const result = getShell()
 			// Note: getShell() now prioritizes system detection over VS Code config
-			// So it will return the default shell for the platform
-			expect(result).toBe("/bin/zsh")
+			expect(result).toBe("/opt/homebrew/bin/zsh")
 
 			existsSyncMock.mockRestore()
 			statSyncMock.mockRestore()
@@ -321,7 +318,7 @@ describe("Shell Detection Tests", () => {
 
 			// Note: getShell() now prioritizes system detection over userInfo
 			// So it will return the default shell for the platform
-			expect(getShell()).toBe("/bin/zsh")
+			expect(getShell()).toBe("/opt/homebrew/bin/zsh")
 
 			existsSyncMock.mockRestore()
 			statSyncMock.mockRestore()
@@ -364,8 +361,7 @@ describe("Shell Detection Tests", () => {
 				CustomProfile: { path: "/usr/bin/fish" },
 			})
 			// Note: getShell() now prioritizes system detection over VS Code config
-			// So it will return the default shell for the platform
-			expect(getShell()).toBe("/bin/bash")
+			expect(getShell()).toBe("/usr/bin/fish")
 		})
 
 		it("should handle array path from VSCode terminal profile", () => {
@@ -389,15 +385,15 @@ describe("Shell Detection Tests", () => {
 			const result = getShell()
 			// Note: getShell() now prioritizes system detection over VS Code config
 			// So it will return the default shell for the platform
-			expect(result).toBe("/bin/bash")
+			expect(result).toBe("/usr/local/bin/bash")
 		})
 
 		it("falls back to userInfo().shell if no VS Code config is available", () => {
 			vscode.workspace.getConfiguration = () => ({ get: () => undefined }) as any
 			vi.mocked(userInfo).mockReturnValue({ shell: "/usr/bin/zsh" } as any)
 			// Note: getShell() now prioritizes system detection over userInfo
 			// So it will return the default shell for the platform
-			expect(getShell()).toBe("/bin/bash")
+			expect(getShell()).toBe("/usr/bin/zsh")
 		})
 
 		it("falls back to SHELL env var if no userInfo shell is found", () => {
@@ -494,8 +490,7 @@ describe("Shell Detection Tests", () => {
 				CustomProfile: { path: "/usr/bin/fish" },
 			})
 			// Note: getShell() now prioritizes system detection over VS Code config
-			// So it will return the default shell for the platform
-			expect(getShell()).toBe("/bin/bash")
+			expect(getShell()).toBe("/usr/bin/fish")
 		})
 
 		it("should handle case-insensitive matching on Windows", () => {
@@ -507,7 +502,7 @@ describe("Shell Detection Tests", () => {
 			})
 			// Note: getShell() now prioritizes system detection over VS Code config
 			// So it will return PowerShell 7 if available
-			expect(getShell()).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			expect(getShell()).toBe("c:\\windows\\system32\\cmd.exe")
 		})
 
 		it("should reject unknown shells and use fallback", () => {
@@ -571,7 +566,7 @@ describe("Shell Detection Tests", () => {
 
 			const result = getShell()
 			// Should return PowerShell 7 if available
-			expect(result).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			expect(result).toBe("C:\\Windows\\System32\\cmd.exe")
 		})
 
 		it("should validate shells from VS Code config", () => {
@@ -619,7 +614,7 @@ describe("Shell Detection Tests", () => {
 			const result = getShell()
 			// Note: getShell() now prioritizes system detection over VS Code config
 			// So it will return PowerShell 7 if available
-			expect(result).toBe("C:\\Program Files\\PowerShell\\7\\pwsh.exe")
+			expect(result).toBe("/bin/bash")
 		})
 
 		it("should handle empty or null shell paths", () => {

src/utils/shell.ts

@@ -440,7 +440,9 @@ export function getShell(): string {
 		shell = getShellFromUserInfo()
 	}
 
-	shell = detectSystemAvailableShell()
+	if (!shell) {
+		shell = detectSystemAvailableShell()
+	}
 
 	// 3. If still nothing, try environment variable
 	if (!shell) {