feat: add --clean-env flag to tasks and run command

docs/features/advanced_tasks.md

@@ -195,6 +195,23 @@ These variables are not shared over tasks, so you need to define these for every
     ```
     This will output `/tmp/path:/usr/bin:/bin` instead of the original `/usr/bin:/bin`.
 
+## Clean environment
+You can make sure the environment of a task is "pixi only".
+Here pixi will only include the minimal required environment variables for your platform to run the command in.
+The environment will contain all variables set by the conda environment like `"CONDA_PREFIX"`.
+It will however include some default values from the shell, like:
+`"DISPLAY"`, `"LC_ALL"`, `"LC_TIME"`, `"LC_NUMERIC"`, `"LC_MEASUREMENT"`, `"SHELL"`, `"USER"`, `"USERNAME"`, `"LOGNAME"`, `"HOME"`, `"HOSTNAME"`,`"TMPDIR"`, `"XPC_SERVICE_NAME"`, `"XPC_FLAGS"`
+
+```toml
+[tasks]
+clean_command = { cmd = "python run_in_isolated_env.py", clean-env = true}
+```
+This setting can also be set from the command line with `pixi run --clean-env TASK_NAME`.
+
+!!! warning "`clean-env` not supported on Windows"
+    On Windows it's hard to create a "clean environment" as `conda-forge` doesn't ship Windows compilers and Windows needs a lot of base variables.
+    Making this feature not worthy of implementing as the amount of edge cases will make it unusable.
+
 ## Our task runner: deno_task_shell
 
 To support the different OS's (Windows, OSX and Linux), pixi integrates a shell that can run on all of them.

docs/reference/cli.md

@@ -178,7 +178,7 @@ You cannot run `pixi run source setup.bash` as `source` is not available in the
 - `--frozen`: install the environment as defined in the lock file, doesn't update `pixi.lock` if it isn't up-to-date with [manifest file](project_configuration.md). It can also be controlled by the `PIXI_FROZEN` environment variable (example: `PIXI_FROZEN=true`).
 - `--locked`: only install if the `pixi.lock` is up-to-date with the [manifest file](project_configuration.md)[^1]. It can also be controlled by the `PIXI_LOCKED` environment variable (example: `PIXI_LOCKED=true`). Conflicts with `--frozen`.
 - `--environment <ENVIRONMENT> (-e)`: The environment to run the task in, if none are provided the default environment will be used or a selector will be given to select the right environment.
-
+- `--clean-env`: Run the task in a clean environment, this will remove all environment variables of the shell environment except for the ones pixi sets. THIS DOESN't WORK ON `Windows`.
 ```shell
 pixi run python
 pixi run cowpy "Hey pixi user"
@@ -192,6 +192,11 @@ pixi run task argument1 argument2
 
 # If you have multiple environments you can select the right one with the --environment flag.
 pixi run --environment cuda python
+
+# THIS DOESN'T WORK ON WINDOWS
+# If you want to run a command in a clean environment you can use the --clean-env flag.
+# The PATH should only contain the pixi environment here.
+pixi run --clean-env "echo \$PATH"
 ```
 
 !!! info

docs/reference/project_configuration.md

@@ -176,6 +176,7 @@ alias = { depends-on=["depending"]}
 download = { cmd="curl -o file.txt https://example.com/file.txt" , outputs=["file.txt"]}
 build = { cmd="npm build", cwd="frontend", inputs=["frontend/package.json", "frontend/*.js"]}
 run = { cmd="python run.py $ARGUMENT", env={ ARGUMENT="value" }}
+clean-env = { cmd = "python isolated.py", clean-env = true} # Only on Unix!
 ```
 
 You can modify this table using [`pixi task`](cli.md#task).