ANSI escape color codes broken on Git Bash in Windows Terminal

[tiesmaster]

Describe the bug
Running the az CLI on Windows using Git Bash in the Windows Terminal shows color output is broken. This is specific to this situation (see below for more context). When running $ az help, the output ends with:

[...more output elided for brevity...]
←[1mFor more specific examples, use: az find "az "←[0m

←[0mPlease let us know how we are doing: ←[96mhttps://aka.ms/azureclihats←[0m
←[0mand let us know if you're interested in trying out our newest features: ←[96mhttps://aka.ms/CLIUXstudy←[0m

To Reproduce

1. Install latest Windows Terminal
2. Install latest Git Bash, and enable the checkbox to add the "Windows Terminal" profile
3. Install latest Azure CLI
4. Start Windows Terminal, and open the Git Bash profile
5. Run: $ az help

Expected behavior
Output is showing colors.

Environment summary

Windows-10-10.0.19041-SP0
Python 3.8.9
Installer: MSI

azure-cli 2.27.1

Windows Terminal
Version: 1.9.1942.0

Git for Windows: 2.33.0.2

Additional context
I ran into this when setting up a new dev box, and also found out the following details:

• when starting the powershell profile within Windows Terminal, the output is colored correctly
• when starting Git Bash from the Start Menu (this uses the mintty terminal that comes preinstalled with the Git for Windows install), the output is not colored, but the escape codes don't appear
• when running the Azure CLI on my old system, the coloring output is working inside the Windows Terminal (same version) in Git Bash. The version of the Azure CLI that's installed there is: 2.15.1
• running ANSI escape sequences like this does ouput colors

---

UPDATE: Results of some additional testing

I wanted to be sure that the reproduction steps are sound on a new system, with pretty much all the defaults, and installing from MSI, or Windows Store (for the Windows Terminal). So I created a new VM in Azure with Windows 10 Pro 20H2, and managed to reproduce this in this fresh box.

I also did some additional research where this broke, so I did a "git bisect" but then via installing the MSIs, and there are my results:

• 2.18: PASS
• 2.20: PASS
• 2.21: PASS
• 2.22: FAIL
• 2.23: FAIL
• 2.27.2: FAIL

Needless to say, version 2.22 broke this.

[yonzhan]

@jiasli for awareness

[jiasli]

Azure CLI has been affected by colorama bugs for a long time (microsoft/knack#209). That's why we stopped initializing colorama in Linux terminals (microsoft/knack#238).

If we check isatty in the original Git Bash terminal, it shows:

$ "/c/Program Files (x86)/Microsoft SDKs/Azure/CLI2/python.exe" -c "import sys; print(sys.stdin.isatty())"
False

This corrupts the color detection logic:

https://github.com/microsoft/knack/blob/03b46abc9735fdc88e90b89b9c88192758a83277/knack/cli.py#L276-L278

        if sys.stdout.isatty() and sys.stderr.isatty() and self.out_file is sys.stdout:
            self.init_debug_log.append("Enable color in terminal.")
            return True

CLI thinks this is not a TTY and turns off the color, even though escape sequences are indeed supported.

$ "/c/Program Files (x86)/Microsoft SDKs/Azure/CLI2/python.exe" -c 'print("\x1b[36mhello world\x1b[0m")'

Found these discussions:

• https://stackoverflow.com/questions/40912072/git-for-windows-mintty-sys-stdout-isatty-returns-false
• Python thinks stdin not connected to a TTY git-for-windows/git#2594

However, in Git Bash running in Windows Terminal, isatty returns True:

$ "/c/Program Files (x86)/Microsoft SDKs/Azure/CLI2/python.exe" -c "import sys; print(sys.stdin.isatty())"
True

But escape sequences can't be displayed correctly:

$ "/c/Program Files (x86)/Microsoft SDKs/Azure/CLI2/python.exe" -c 'print("\x1b[36mhello world\x1b[0m")'

Discussions on the topic:

• Using Windows Terminal with a git-for-windows tab displays odd characters git-for-windows/git#2483
• Escape sequences behave strangely over conpty when VirtualTerminalLevel is set microsoft/terminal#1965

So this is actually a "Git Bash in Windows Terminal" problem.

For now, I would recommend these workarounds:

• Disable color with the no_color configuration:

  az config set core.no_color=True
  

• Use other shells (like PowerShell, WSL) officially supported by Azure CLI

[tiesmaster]

@jiasli Thanks for the detailed write-up. I suspected it was a simple regression, perhaps pulling in a new version of a 3rd party dependency that regressed, however, it's not unsurprising that the plot thickens this much with things like git-for-windows, and the WT 😅

The workaround is really helpful, I didn't knew about that. It really makes the output usable, and made my day ❤️ Thnx!

[jiasli]

I am glad to know the workaround works for you! Please free feel to contact us if there are any problems. 😊