Invert the logic for determining if a path is a base conda environment

crates/uv-python/src/lib.rs

@@ -1198,7 +1198,7 @@ mod tests {
             "We should allow the active conda python"
         );
 
-        let baseenv = context.tempdir.child("base");
+        let baseenv = context.tempdir.child("conda");
         TestContext::mock_conda_prefix(&baseenv, "3.12.1")?;
 
         // But not if it's a base environment
@@ -1224,21 +1224,23 @@ mod tests {
         );
 
         // Unless, system interpreters are included...
-        let python = context.run_with_vars(
-            &[
-                ("CONDA_PREFIX", Some(baseenv.as_os_str())),
-                ("CONDA_DEFAULT_ENV", Some(&OsString::from("base"))),
-            ],
-            || {
-                find_python_installation(
-                    &PythonRequest::Default,
-                    EnvironmentPreference::OnlySystem,
-                    PythonPreference::OnlySystem,
-                    &context.cache,
-                    Preview::default(),
-                )
-            },
-        )??;
+        let python = context
+            .run_with_vars(
+                &[
+                    ("CONDA_PREFIX", Some(baseenv.as_os_str())),
+                    ("CONDA_DEFAULT_ENV", Some(&OsString::from("base"))),
+                ],
+                || {
+                    find_python_installation(
+                        &PythonRequest::Default,
+                        EnvironmentPreference::OnlySystem,
+                        PythonPreference::OnlySystem,
+                        &context.cache,
+                        Preview::default(),
+                    )
+                },
+            )?
+            .unwrap();
 
         assert_eq!(
             python.interpreter().python_full_version().to_string(),
@@ -1247,21 +1249,23 @@ mod tests {
         );
 
         // If the environment name doesn't match the default, we should not treat it as system
-        let python = context.run_with_vars(
-            &[
-                ("CONDA_PREFIX", Some(condaenv.as_os_str())),
-                ("CONDA_DEFAULT_ENV", Some(&OsString::from("base"))),
-            ],
-            || {
-                find_python_installation(
-                    &PythonRequest::Default,
-                    EnvironmentPreference::OnlyVirtual,
-                    PythonPreference::OnlySystem,
-                    &context.cache,
-                    Preview::default(),
-                )
-            },
-        )??;
+        let python = context
+            .run_with_vars(
+                &[
+                    ("CONDA_PREFIX", Some(condaenv.as_os_str())),
+                    ("CONDA_DEFAULT_ENV", Some(&OsString::from("condaenv"))),
+                ],
+                || {
+                    find_python_installation(
+                        &PythonRequest::Default,
+                        EnvironmentPreference::OnlyVirtual,
+                        PythonPreference::OnlySystem,
+                        &context.cache,
+                        Preview::default(),
+                    )
+                },
+            )?
+            .unwrap();
 
         assert_eq!(
             python.interpreter().python_full_version().to_string(),

crates/uv-python/src/virtualenv.rs

@@ -82,25 +82,30 @@ impl CondaEnvironmentKind {
     /// When the base environment is used, `CONDA_DEFAULT_ENV` will be set to a name, i.e., `base` or
     /// `root` which does not match the prefix, e.g. `/usr/local` instead of
     /// `/usr/local/conda/envs/<name>`.
+    ///
+    /// Note the name `CONDA_DEFAULT_ENV` is misleading, it's the current environment, not the base
+    /// environment name.
     fn from_prefix_path(path: &Path) -> Self {
         // If we cannot read `CONDA_DEFAULT_ENV`, there's no way to know if the base environment
-        let Ok(default_env) = env::var(EnvVars::CONDA_DEFAULT_ENV) else {
+        let Ok(current_env) = env::var(EnvVars::CONDA_DEFAULT_ENV) else {
             return Self::Child;
         };
 
         // These are the expected names for the base environment
-        if default_env != "base" && default_env != "root" {
+        if current_env != "base" && current_env != "root" {
             return Self::Child;
         }
 
         let Some(name) = path.file_name() else {
             return Self::Child;
         };
 
-        if name.to_str().is_some_and(|name| name == default_env) {
-            Self::Base
-        } else {
+        // If the environment is in a directory matching the name of the environment, it's not
+        // usually a base environment.
+        if name.to_str().is_some_and(|name| name == current_env) {
             Self::Child
+        } else {
+            Self::Base
         }
     }
 }