Fixes venv and conda pip installation on windows (#970)

# Description

The current windows installation does not support pip installation of
isaac sim in venv as it only checks whether a conda environment is
enabled or assumes that a symlink to isaac sim is used. This change adds
support to check for system python when isaac sim is installed via pip.
In addition, isaac sim variables at conda environment startup should
only be assigned if isaac sim is installed from binary. This change
addresses the need for when pip installation of isaac sim is used in
conda.


## Type of change

<!-- As you go through the list, delete the ones that are not
applicable. -->

- Bug fix (non-breaking change which fixes an issue)


## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

<!--
As you go through the checklist above, you can mark something as done by
putting an x character in it

For example,
- [x] I have done this task
- [ ] I have not done this task
-->

isaaclab.bat

@@ -14,26 +14,19 @@ rem Helper functions
 
 rem extract Isaac Sim directory
 :extract_isaacsim_path
-rem check if conda environment is activated and isaacsim package is installed
-if not "%CONDA_PREFIX%"=="" (
-    rem use conda python
-    set python_exe=%CONDA_PREFIX%\python
-    call !python_exe! -m pip show isaacsim-rl > nul 2>&1
-    if errorlevel 1 (
-        rem Use the sym-link path to Isaac Sim directory
-        set isaac_path=%ISAACLAB_PATH%\_isaac_sim
-    ) else (
-        rem retrieve the isaacsim path from the installed package
-        set "isaac_path="
-        for /f "delims=" %%i in ('!python_exe! -c "import isaacsim; import os; print(os.environ['ISAAC_PATH'])"') do (
-            if not defined isaac_path (
-                set "isaac_path=%%i"
-            )
+rem Use the sym-link path to Isaac Sim directory
+set isaac_path=%ISAACLAB_PATH%\_isaac_sim
+rem Check if directory exists
+if not exist "%isaac_path%" (
+    rem Find the Python executable
+    call :extract_python_exe
+    rem retrieve the isaacsim path from the installed package
+    set "isaac_path="
+    for /f "delims=" %%i in ('!python_exe! -c "import isaacsim; import os; print(os.environ['ISAAC_PATH'])"') do (
+        if not defined isaac_path (
+            set "isaac_path=%%i"
         )
     )
-) else (
-    rem Use the sym-link path to Isaac Sim directory
-    set isaac_path=%ISAACLAB_PATH%\_isaac_sim
 )
 rem Check if the directory exists
 if not exist "%isaac_path%" (
@@ -50,16 +43,25 @@ rem extract the python from isaacsim
 rem check if using conda
 if not "%CONDA_PREFIX%"=="" (
     rem use conda python
-    set python_exe=%CONDA_PREFIX%\python
+    set python_exe=%CONDA_PREFIX%\python.exe
 ) else (
-    rem obtain isaacsim path
-    call :extract_isaacsim_path
-    rem use python from kit if Isaac Sim not installed from pip
-    set python_exe=!isaac_path!\python.bat
+    rem use kit python
+    set python_exe=%ISAACLAB_PATH%\_isaac_sim\python.bat
 )
-rem check if there is a python path available
-if "%python_exe%"=="" (
-    echo [ERROR] Unable to find any Python executable at path: %isaac_path%
+rem check for if isaac sim was installed to system python
+if not exist "%python_exe%" (
+    set "python_exe="
+    python -m pip show isaacsim-rl > nul 2>&1
+    if %ERRORLEVEL% equ 0 (
+        for /f "delims=" %%i in ('where python') do (
+            if not defined python_exe (
+                set "python_exe=%%i"
+            )
+        )
+    )
+)
+if not exist "%python_exe%" (
+    echo [ERROR] Unable to find any Python executable at path: %python_exe%
     echo %tab%This could be due to the following reasons:
     echo %tab%1. Conda environment is not activated.
     echo %tab%2. Python executable is not available at the default path: %ISAACLAB_PATH%\_isaac_sim\python.bat
@@ -83,7 +85,7 @@ if errorlevel 1 (
 )
 rem check if there is a python path available
 if not exist "%isaacsim_exe%" (
-    echo [ERROR] No isaac-sim executable found at path: !isaac_path!
+    echo [ERROR] No isaac-sim executable found at path: %isaacsim_exe%
     exit /b 1
 )
 goto :eof
@@ -135,27 +137,42 @@ mkdir "%CONDA_PREFIX%\etc\conda\deactivate.d" 2>nul
 
 rem obtain isaacsim path
 call :extract_isaacsim_path
-
-rem add variables to environment during activation
-(
-    echo @echo off
-    echo rem for isaac-sim
-    echo set "RESOURCE_NAME=IsaacSim"
-    echo set CARB_APP_PATH=!isaac_path!\kit
-    echo set EXP_PATH=!isaac_path!\apps
-    echo set ISAAC_PATH=!isaac_path!
-    echo set PYTHONPATH=%PYTHONPATH%;!isaac_path!\site
-    echo.
-    echo rem for isaac-lab
-    echo doskey isaaclab=isaaclab.bat $*
-) > "%CONDA_PREFIX%\etc\conda\activate.d\env_vars.bat"
-(
-    echo $env:CARB_APP_PATH="!isaac_path!\kit"
-    echo $env:EXP_PATH="!isaac_path!\apps"
-    echo $env:ISAAC_PATH="!isaac_path!"
-    echo $env:PYTHONPATH="%PYTHONPATH%;!isaac_path!\site"
-    echo $env:RESOURCE_NAME="IsaacSim"
-) > "%CONDA_PREFIX%\etc\conda\activate.d\env_vars.ps1"
+if exist "%isaac_path%" (
+    rem add variables to environment during activation
+    (
+        echo @echo off
+        echo rem for isaac-sim
+        echo set "RESOURCE_NAME=IsaacSim"
+        echo set CARB_APP_PATH=!isaac_path!\kit
+        echo set EXP_PATH=!isaac_path!\apps
+        echo set ISAAC_PATH=!isaac_path!
+        echo set PYTHONPATH=%PYTHONPATH%;!isaac_path!\site
+        echo.
+        echo rem for isaac-lab
+        echo doskey isaaclab=isaaclab.bat $*
+    ) > "%CONDA_PREFIX%\etc\conda\activate.d\env_vars.bat"
+    (
+        echo $env:CARB_APP_PATH="!isaac_path!\kit"
+        echo $env:EXP_PATH="!isaac_path!\apps"
+        echo $env:ISAAC_PATH="!isaac_path!"
+        echo $env:PYTHONPATH="%PYTHONPATH%;!isaac_path!\site"
+        echo $env:RESOURCE_NAME="IsaacSim"
+    ) > "%CONDA_PREFIX%\etc\conda\activate.d\env_vars.ps1"
+) else (
+    rem assume isaac sim will be installed from pip
+    rem add variables to environment during activation
+    (
+        echo @echo off
+        echo rem for isaac-sim
+        echo set "RESOURCE_NAME=IsaacSim"
+        echo.
+        echo rem for isaac-lab
+        echo doskey isaaclab=isaaclab.bat $*
+    ) > "%CONDA_PREFIX%\etc\conda\activate.d\env_vars.bat"
+    (
+        echo $env:RESOURCE_NAME="IsaacSim"
+    ) > "%CONDA_PREFIX%\etc\conda\activate.d\env_vars.ps1"
+)
 
 rem reactivate the environment to load the variables
 call conda activate %env_name%