Add VIRTUAL_ENV to env var when running in a venv (#16425)

Activating a virtual environment sets a VIRTUAL_ENV environment
variable. Replicate this behaviour in `ActivateVirtualEnv` function.

https://docs.python.org/3/library/venv.html#how-venvs-work
> When a virtual environment has been activated, the VIRTUAL_ENV
environment variable is set to the path of the environment

changelog/pending/20240620--sdk-python--add-virtual_env-environment-variable-when-running-inside-a-virtual-environment.yaml

@@ -0,0 +1,4 @@
+changes:
+- type: fix
+  scope: sdk/python
+  description: Add VIRTUAL_ENV environment variable when running inside a virtual environment

sdk/python/toolchain/pip.go

@@ -331,8 +331,8 @@ func NewVirtualEnvError(dir, fullPath string) error {
 
 // ActivateVirtualEnv takes an array of environment variables (same format as os.Environ()) and path to
 // a virtual environment directory, and returns a new "activated" array with the virtual environment's
-// "bin" dir ("Scripts" on Windows) prepended to the `PATH` environment variable and `PYTHONHOME` variable
-// removed.
+// "bin" dir ("Scripts" on Windows) prepended to the `PATH` environment variable, the `VIRTUAL_ENV`
+// variable set to the path, and the `PYTHONHOME` variable removed.
 func ActivateVirtualEnv(environ []string, virtualEnvDir string) []string {
 	virtualEnvBin := filepath.Join(virtualEnvDir, virtualEnvBinDirName())
 	var hasPath bool
@@ -351,6 +351,8 @@ func ActivateVirtualEnv(environ []string, virtualEnvDir string) []string {
 			result = append(result, path)
 		} else if strings.EqualFold(key, "PYTHONHOME") {
 			// Skip PYTHONHOME to "unset" this value.
+		} else if strings.EqualFold(key, "VIRTUAL_ENV") {
+			// Skip VIRTUAL_ENV, we always set this to `virtualEnvDir`
 		} else {
 			result = append(result, env)
 		}
@@ -359,6 +361,8 @@ func ActivateVirtualEnv(environ []string, virtualEnvDir string) []string {
 		path := "PATH=" + virtualEnvBin
 		result = append(result, path)
 	}
+	virtualEnv := "VIRTUAL_ENV=" + virtualEnvDir
+	result = append(result, virtualEnv)
 	return result
 }
 

sdk/python/toolchain/pip_test.go

@@ -50,27 +50,38 @@ func TestIsVirtualEnv(t *testing.T) {
 func TestActivateVirtualEnv(t *testing.T) {
 	t.Parallel()
 
-	venvName := "venv"
-	venvDir := filepath.Join(venvName, "bin")
+	venvDir := "/some/path/venv"
+	venvBinDir := filepath.Join(venvDir, "bin")
 	if runtime.GOOS == windows {
-		venvDir = filepath.Join(venvName, "Scripts")
+		venvBinDir = filepath.Join(venvDir, "Scripts")
 	}
 
 	tests := []struct {
 		input    []string
 		expected []string
 	}{
 		{
-			input:    []string{"PYTHONHOME=foo", "PATH=bar", "FOO=blah"},
-			expected: []string{fmt.Sprintf("PATH=%s%sbar", venvDir, string(os.PathListSeparator)), "FOO=blah"},
+			input: []string{"PYTHONHOME=foo", "PATH=bar", "FOO=blah"},
+			expected: []string{
+				fmt.Sprintf("PATH=%s%sbar", venvBinDir, string(os.PathListSeparator)),
+				"FOO=blah",
+				"VIRTUAL_ENV=" + venvDir,
+			},
 		},
 		{
-			input:    []string{"PYTHONHOME=foo", "FOO=blah"},
-			expected: []string{"FOO=blah", "PATH=" + venvDir},
+			input: []string{"PYTHONHOME=foo", "FOO=blah"},
+			expected: []string{
+				"FOO=blah",
+				"PATH=" + venvBinDir,
+				"VIRTUAL_ENV=" + venvDir,
+			},
 		},
 		{
-			input:    []string{"PythonHome=foo", "Path=bar"},
-			expected: []string{fmt.Sprintf("Path=%s%sbar", venvDir, string(os.PathListSeparator))},
+			input: []string{"PythonHome=foo", "Path=bar"},
+			expected: []string{
+				fmt.Sprintf("Path=%s%sbar", venvBinDir, string(os.PathListSeparator)),
+				"VIRTUAL_ENV=" + venvDir,
+			},
 		},
 	}
 	//nolint:paralleltest // false positive because range var isn't used directly in t.Run(name) arg
@@ -79,7 +90,7 @@ func TestActivateVirtualEnv(t *testing.T) {
 		t.Run(fmt.Sprintf("%#v", test.input), func(t *testing.T) {
 			t.Parallel()
 
-			actual := ActivateVirtualEnv(test.input, venvName)
+			actual := ActivateVirtualEnv(test.input, venvDir)
 			assert.Equal(t, test.expected, actual)
 		})
 	}