Clear prompt input value when onDidEndShellExecution

[anthonykim1]

Resolves: microsoft/vscode-python-environments#640

Assumption: activate command always run first before python file command.
This is now fact thanks to microsoft/vscode-python-environments#1088

When python-envs.terminal.autoActivationType us command with "python.useEnvironmentsExtension": true,:
---> Ctrl+c is displayed when pressing the run button to run Python file.
Specific location of this ctrl+c is after activate command, but before python file execution command.

What is happening:

1. Environment extension wait for onDidTerminalShellExecutionEnd where we wait for activation command (this should be the first thing that runs in the terminal)
2. Then we executeCommand() again (to run Python file.) This is when user presses the run button to run python file.
3. (Bug) Ctrl+c is shown.
4. But why is ctrl+ c shown? After debugging, it turns out the prompt input model value is still showing activate command. Not the empty nor the python file command.

Maybe conpty related bugs, hence why we've been getting more reports from windows users.
Decoration location is off too.

---

How to resolve (below are options we can take):

1. Wait for conpty v.1.25 to stabilize shell integration decoration
2. clear prompt input value when onDidEndShellExecution (this PR).
3. Await (short like 500ms) hard-coded timeout in extension after activation prompt.
4. Do option 2 first then consider removing once we have option 1?

Image of the problem:

[Copilot]

Pull request overview

This PR addresses a bug where Ctrl+C is incorrectly shown when running Python files after activation commands in the terminal. The issue occurs because the prompt input model retains stale command values between shell executions, particularly on Windows systems with conpty.

Key changes:

• Adds a clearValue() method to the IPromptInputModel interface and PromptInputModel class to clear prompt input state
• Calls clearValue() in the onDidEndTerminalShellExecution event handler to prevent stale input values from persisting between commands

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
src/vs/platform/terminal/common/capabilities/commandDetection/promptInputModel.ts	Adds clearValue() method to clear the prompt input value after command execution
src/vs/workbench/api/browser/mainThreadTerminalShellIntegration.ts	Calls clearValue() when shell execution ends to prevent stale input from showing in subsequent commands

[Copilot]

The clearValue method only clears the _value field but leaves other state fields like _cursorIndex, _ghostTextIndex, _state, _commandStartMarker, and _commandStartX unchanged. This creates an inconsistent state where the value is empty but other tracking fields still reference the old command. Consider also resetting these fields or at minimum _cursorIndex and _ghostTextIndex to maintain state consistency. Looking at _handleCommandStart (line 219-220), it clears both _value and _cursorIndex together.

Suggested change

	this._value = '';
	this._value = '';
	this._cursorIndex = 0;
	this._ghostTextIndex = -1;

[Copilot]

The clearValue method doesn't trigger any events (onDidChangeInput) after clearing the value. This means subscribers won't be notified of the state change. Compare this to _handleCommandExecuted (line 267) which fires onDidChangeInput after modifying state, and _handleCommandStart (line 222) which also fires events. If extensions or other components are listening to these events to track the prompt state, they won't be notified when the value is cleared, potentially causing them to have stale state as well.

Suggested change

	this._value = '';
	this._value = '';
	this._onDidChangeInput.fire(this._createStateObject());

[Copilot]

Calling clearValue() on the promptInputModel in the onCommandFinished event handler could cause timing issues. According to the PR description, the problem occurs when an activation command finishes and a Python file command is about to run. The clearValue is called during onCommandFinished which happens after onCommandExecuted (see line 246-268 where _handleCommandExecuted transitions state to Execute and fires events). However, the next command hasn't started yet (which would call _handleCommandStart at line 211-234 and properly initialize state). This creates a window where the model is in an inconsistent state between commands. The timing issue mentioned in the PR description about needing a 500ms timeout suggests this workaround may not fully solve the race condition.

Suggested change

	currentCommand = undefined;
	const instanceId = e.instance.instanceId;
	instanceDataListeners.get(instanceId)?.dispose();
	// Clear the prompt input value before sending the event to the extension host
	// so that subsequent executeCommand calls don't see stale input
	e.instance.capabilities.get(TerminalCapability.CommandDetection)?.promptInputModel.clearValue();
	const activeCommand = currentCommand;
	const instanceId = e.instance.instanceId;
	instanceDataListeners.get(instanceId)?.dispose();
	// Clear the prompt input value before sending the event to the extension host
	// so that subsequent executeCommand calls don't see stale input. Only clear if
	// no newer command has become active since this one started.
	if (!activeCommand || activeCommand.commandLine === e.data.command) {
	e.instance.capabilities.get(TerminalCapability.CommandDetection)?.promptInputModel.clearValue();
	}
	currentCommand = undefined;

[Copilot]

The new clearValue method lacks test coverage. There is a comprehensive test file at src/vs/platform/terminal/test/common/capabilities/commandDetection/promptInputModel.test.ts with tests for other prompt input model behaviors. Consider adding tests that verify clearValue properly clears the state and handles edge cases like calling clearValue multiple times or calling it in different states (Input, Execute, Unknown).

[anthonykim1]

Much better when we clear prompt input at onDidEndShellExecution
https://github.com/user-attachments/assets/7aa4d2c0-1c09-47f5-b5ad-ea938a3b8630