Fix missing encoding of backslash in terminal shell integration environment variable values

[abrahan-munro]

A colon is used as a separator for environment variables to be set in the shell via terminal shell integration. Colons in the values are encoded as a backslash escape sequence and decoded with echo -e.

However, as backslash is not also encoded, any existing backslash may be treated as an escape sequence when decoding. This is visible on Windows when using bash with the Python extension and a username that starts with a character that is recognised in a backslash escape sequence, as HOME will then be set incorrectly.

This change fixes the bug by encoding any backslash characters.

Resolves #240539. See for more details.

May also deal with microsoft/vscode-python#23604, #227223, #212508, #212487, #212958, microsoft/vscode-python#24717, etc.

[Tyriar]

Thanks for the investigation, do you know how to reproduce the problem though? This is what I see:

I have 3 extensions contributing to the environment:

# Terminal Environment Changes

## Extension: ms-python.python

- `PYTHONSTARTUP=c:\Users\Daniel\AppData\Roaming\Code - Insiders\User\workspaceStorage\54d3aa32f66add3fc5bf0ed69305c70a\ms-python.python\pythonrc.py`

## Extension: GitHub.copilot-chat

Enables use of the `copilot-debug` command in the terminal.

- `PATH=${env:PATH};c:\Users\Daniel\AppData\Roaming\Code - Insiders\User\globalStorage\github.copilot-chat\debugCommand`

## Extension: vscode.git

Enables the following features: git auth provider

- `GIT_ASKPASS=c:\Users\Daniel\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\git\dist\askpass.sh`
- `VSCODE_GIT_ASKPASS_NODE=C:\Users\Daniel\AppData\Local\Programs\Microsoft VS Code Insiders\Code - Insiders.exe`
- `VSCODE_GIT_ASKPASS_EXTRA_ARGS=`
- `VSCODE_GIT_ASKPASS_MAIN=c:\Users\Daniel\AppData\Local\Programs\Microsoft VS Code Insiders\resources\app\extensions\git\dist\askpass-main.js`
- `VSCODE_GIT_IPC_HANDLE=\\.\pipe\vscode-git-4523965613-sock`

It may be one of your extensions?

[Tyriar]

and a username that starts with a character that is recognised in a backslash escape sequence

I might not be understanding this right?

[abrahan-munro]

This will only be seen when the value of the environment variable being encoded includes an escape sequence supported by echo -e. This is likely to happen with windows-style paths (i.e. \ path separator) and file or directory names starting with one of the characters used in an escape sequence (i.e. a, b, c, e, E, f, n, r, t, or v, also possibly 0, x, u, or U, depending on the next characters).

In my case, without the Python extension, terminal shell integration is inactive and HOME has the default value of /c/Users/abrahan. With the Python extension, terminal shell integration is active, and it is trying to set HOME to C:\Users\abrahan (🤷). But the \a is being interpreted as an escape sequence.

The issue and fix can be demonstrated as follows.

Without the fix:

$ encoded=$(node -e 'function _encodeColons(value) { return value.replaceAll(":", "\\x3a"); } console.log(_encodeColons(String.raw`C:\Users\abrahan`));'); echo "$encoded"; echo -e "$encoded"
C\x3a\Users\abrahan
C:\Usersbrahan

With the fix:

$ encoded=$(node -e 'function _encodeColons(value) { return value.replaceAll("\\", "\\\\").replaceAll(":", "\\x3a"); } console.log(_encodeColons(String.raw`C:\Users\abrahan`));'); echo "$encoded"; echo -e "$encoded"
C\x3a\\Users\\abrahan
C:\Users\abrahan

[Tyriar]

Oh I see, the trigger then is the Python's environment activation that replaces the PATH variable and it's not git bash aware. That feature is likely going to be removed soon (microsoft/vscode-python#24717 (comment)), but the encoding fix does look good