[ty] distinguish base conda from child conda (#19990)

This is a port of the logic in https://github.com/astral-sh/uv/pull/7691

The basic idea is we use CONDA_DEFAULT_ENV as a signal for whether
CONDA_PREFIX is just the ambient system conda install, or the user has
explicitly activated a custom one. If the former, then the conda is
treated like a system install (having lowest priority). If the latter,
the conda is treated like an activated venv (having priority over
everything but an Actual activated venv).

Fixes https://github.com/astral-sh/ty/issues/611

crates/ty/tests/cli/python_environment.rs

@@ -900,59 +900,165 @@ fn defaults_to_a_new_python_version() -> anyhow::Result<()> {
 /// The `site-packages` directory is used by ty for external import.
 /// Ty does the following checks to discover the `site-packages` directory in the order:
 /// 1) If `VIRTUAL_ENV` environment variable is set
-/// 2) If `CONDA_PREFIX` environment variable is set
+/// 2) If `CONDA_PREFIX` environment variable is set (and .filename != `CONDA_DEFAULT_ENV`)
 /// 3) If a `.venv` directory exists at the project root
+/// 4) If `CONDA_PREFIX` environment variable is set (and .filename == `CONDA_DEFAULT_ENV`)
 ///
-/// This test is aiming at validating the logic around `CONDA_PREFIX`.
+/// This test (and the next one) is aiming at validating the logic around these cases.
 ///
-/// A conda-like environment file structure is used
+/// To do this we create a program that has these 4 imports:
-/// We test by first not setting the `CONDA_PREFIX` and expect a fail.
+///
-/// Then we test by setting `CONDA_PREFIX` to `conda-env` and expect a pass.
+/// ```python
+/// from package1 import ActiveVenv
+/// from package1 import ChildConda
+/// from package1 import WorkingVenv
+/// from package1 import BaseConda
+/// ```
+///
+/// We then create 4 different copies of package1. Each copy defines all of these
+/// classes... except the one that describes it. Therefore we know we got e.g.
+/// the working venv if we get a diagnostic like this:
+///
+/// ```text
+/// Unresolved import
+/// 4 | from package1 import WorkingVenv
+///   |                      ^^^^^^^^^^^
+/// ```
+///
+/// This test uses a directory structure as follows:
 ///
 /// ├── project
-/// │   └── test.py
+/// │   ├── test.py
-/// └── conda-env
+/// │   └── .venv
-///     └── lib
+/// │       ├── pyvenv.cfg
-///         └── python3.13
+/// │       └── lib
-///             └── site-packages
+/// │           └── python3.13
-///                 └── package1
+/// │               └── site-packages
-///                     └── __init__.py
+/// │                   └── package1
+/// │                       └── __init__.py
+/// ├── myvenv
+/// │   ├── pyvenv.cfg
+/// │   └── lib
+/// │       └── python3.13
+/// │           └── site-packages
+/// │               └── package1
+/// │                   └── __init__.py
+/// ├── conda-env
+/// │   └── lib
+/// │       └── python3.13
+/// │           └── site-packages
+/// │               └── package1
+/// │                   └── __init__.py
+/// └── conda
+///     └── envs
+///         └── base
+///             └── lib
+///                 └── python3.13
+///                     └── site-packages
+///                         └── package1
+///                             └── __init__.py
 ///
 /// test.py imports package1
 /// And the command is run in the `child` directory.
 #[test]
-fn check_conda_prefix_var_to_resolve_path() -> anyhow::Result<()> {
+fn check_venv_resolution_with_working_venv() -> anyhow::Result<()> {
-    let conda_package1_path = if cfg!(windows) {
+    let child_conda_package1_path = if cfg!(windows) {
         "conda-env/Lib/site-packages/package1/__init__.py"
     } else {
         "conda-env/lib/python3.13/site-packages/package1/__init__.py"
     };
 
+    let base_conda_package1_path = if cfg!(windows) {
+        "conda/envs/base/Lib/site-packages/package1/__init__.py"
+    } else {
+        "conda/envs/base/lib/python3.13/site-packages/package1/__init__.py"
+    };
+
+    let working_venv_package1_path = if cfg!(windows) {
+        "project/.venv/Lib/site-packages/package1/__init__.py"
+    } else {
+        "project/.venv/lib/python3.13/site-packages/package1/__init__.py"
+    };
+
+    let active_venv_package1_path = if cfg!(windows) {
+        "myvenv/Lib/site-packages/package1/__init__.py"
+    } else {
+        "myvenv/lib/python3.13/site-packages/package1/__init__.py"
+    };
+
     let case = CliTest::with_files([
         (
             "project/test.py",
             r#"
-            import package1
+            from package1 import ActiveVenv
+            from package1 import ChildConda
+            from package1 import WorkingVenv
+            from package1 import BaseConda
             "#,
         ),
         (
-            conda_package1_path,
+            "project/.venv/pyvenv.cfg",
             r#"
+home = ./
+
+            "#,
+        ),
+        (
+            "myvenv/pyvenv.cfg",
+            r#"
+home = ./
+
+            "#,
+        ),
+        (
+            active_venv_package1_path,
+            r#"
+            class ChildConda: ...
+            class WorkingVenv: ...
+            class BaseConda: ...
+            "#,
+        ),
+        (
+            child_conda_package1_path,
+            r#"
+            class ActiveVenv: ...
+            class WorkingVenv: ...
+            class BaseConda: ...
+            "#,
+        ),
+        (
+            working_venv_package1_path,
+            r#"
+            class ActiveVenv: ...
+            class ChildConda: ...
+            class BaseConda: ...
+            "#,
+        ),
+        (
+            base_conda_package1_path,
+            r#"
+            class ActiveVenv: ...
+            class ChildConda: ...
+            class WorkingVenv: ...
             "#,
         ),
     ])?;
 
-    assert_cmd_snapshot!(case.command().current_dir(case.root().join("project")), @r"
+    // Run with nothing set, should find the working venv
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project")), @r"
     success: false
     exit_code: 1
     ----- stdout -----
-    error[unresolved-import]: Cannot resolve imported module `package1`
+    error[unresolved-import]: Module `package1` has no member `WorkingVenv`
-     --> test.py:2:8
+     --> test.py:4:22
       |
-    2 | import package1
+    2 | from package1 import ActiveVenv
-      |        ^^^^^^^^
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+      |                      ^^^^^^^^^^^
+    5 | from package1 import BaseConda
       |
-    info: make sure your Python environment is properly configured: https://docs.astral.sh/ty/modules/#python-environment
     info: rule `unresolved-import` is enabled by default
 
     Found 1 diagnostic
@@ -961,12 +1067,373 @@ fn check_conda_prefix_var_to_resolve_path() -> anyhow::Result<()> {
     WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
     ");
 
-    // do command : CONDA_PREFIX=<temp_dir>/conda_env
+    // Run with VIRTUAL_ENV set, should find the active venv
-    assert_cmd_snapshot!(case.command().current_dir(case.root().join("project")).env("CONDA_PREFIX", case.root().join("conda-env")), @r"
+    assert_cmd_snapshot!(case.command()
-    success: true
+        .current_dir(case.root().join("project"))
-    exit_code: 0
+        .env("VIRTUAL_ENV", case.root().join("myvenv")), @r"
+    success: false
+    exit_code: 1
     ----- stdout -----
-    All checks passed!
+    error[unresolved-import]: Module `package1` has no member `ActiveVenv`
+     --> test.py:2:22
+      |
+    2 | from package1 import ActiveVenv
+      |                      ^^^^^^^^^^
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // run with CONDA_PREFIX set, should find the child conda
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("CONDA_PREFIX", case.root().join("conda-env")), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `ChildConda`
+     --> test.py:3:22
+      |
+    2 | from package1 import ActiveVenv
+    3 | from package1 import ChildConda
+      |                      ^^^^^^^^^^
+    4 | from package1 import WorkingVenv
+    5 | from package1 import BaseConda
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // run with CONDA_PREFIX and CONDA_DEFAULT_ENV set (unequal), should find child conda
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("CONDA_PREFIX", case.root().join("conda-env"))
+        .env("CONDA_DEFAULT_ENV", "base"), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `ChildConda`
+     --> test.py:3:22
+      |
+    2 | from package1 import ActiveVenv
+    3 | from package1 import ChildConda
+      |                      ^^^^^^^^^^
+    4 | from package1 import WorkingVenv
+    5 | from package1 import BaseConda
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // run with CONDA_PREFIX and CONDA_DEFAULT_ENV (unequal) and VIRTUAL_ENV set,
+    // should find child active venv
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("CONDA_PREFIX", case.root().join("conda-env"))
+        .env("CONDA_DEFAULT_ENV", "base")
+        .env("VIRTUAL_ENV", case.root().join("myvenv")), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `ActiveVenv`
+     --> test.py:2:22
+      |
+    2 | from package1 import ActiveVenv
+      |                      ^^^^^^^^^^
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // run with CONDA_PREFIX and CONDA_DEFAULT_ENV (equal!) set, should find working venv
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("CONDA_PREFIX", case.root().join("conda/envs/base"))
+        .env("CONDA_DEFAULT_ENV", "base"), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `WorkingVenv`
+     --> test.py:4:22
+      |
+    2 | from package1 import ActiveVenv
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+      |                      ^^^^^^^^^^^
+    5 | from package1 import BaseConda
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    Ok(())
+}
+
+/// The exact same test as above, but without a working venv
+///
+/// In this case the Base Conda should be a possible outcome.
+#[test]
+fn check_venv_resolution_without_working_venv() -> anyhow::Result<()> {
+    let child_conda_package1_path = if cfg!(windows) {
+        "conda-env/Lib/site-packages/package1/__init__.py"
+    } else {
+        "conda-env/lib/python3.13/site-packages/package1/__init__.py"
+    };
+
+    let base_conda_package1_path = if cfg!(windows) {
+        "conda/envs/base/Lib/site-packages/package1/__init__.py"
+    } else {
+        "conda/envs/base/lib/python3.13/site-packages/package1/__init__.py"
+    };
+
+    let active_venv_package1_path = if cfg!(windows) {
+        "myvenv/Lib/site-packages/package1/__init__.py"
+    } else {
+        "myvenv/lib/python3.13/site-packages/package1/__init__.py"
+    };
+
+    let case = CliTest::with_files([
+        (
+            "project/test.py",
+            r#"
+            from package1 import ActiveVenv
+            from package1 import ChildConda
+            from package1 import WorkingVenv
+            from package1 import BaseConda
+            "#,
+        ),
+        (
+            "myvenv/pyvenv.cfg",
+            r#"
+home = ./
+
+            "#,
+        ),
+        (
+            active_venv_package1_path,
+            r#"
+            class ChildConda: ...
+            class WorkingVenv: ...
+            class BaseConda: ...
+            "#,
+        ),
+        (
+            child_conda_package1_path,
+            r#"
+            class ActiveVenv: ...
+            class WorkingVenv: ...
+            class BaseConda: ...
+            "#,
+        ),
+        (
+            base_conda_package1_path,
+            r#"
+            class ActiveVenv: ...
+            class ChildConda: ...
+            class WorkingVenv: ...
+            "#,
+        ),
+    ])?;
+
+    // Run with nothing set, should fail to find anything
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project")), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Cannot resolve imported module `package1`
+     --> test.py:2:6
+      |
+    2 | from package1 import ActiveVenv
+      |      ^^^^^^^^
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+      |
+    info: make sure your Python environment is properly configured: https://docs.astral.sh/ty/modules/#python-environment
+    info: rule `unresolved-import` is enabled by default
+
+    error[unresolved-import]: Cannot resolve imported module `package1`
+     --> test.py:3:6
+      |
+    2 | from package1 import ActiveVenv
+    3 | from package1 import ChildConda
+      |      ^^^^^^^^
+    4 | from package1 import WorkingVenv
+    5 | from package1 import BaseConda
+      |
+    info: make sure your Python environment is properly configured: https://docs.astral.sh/ty/modules/#python-environment
+    info: rule `unresolved-import` is enabled by default
+
+    error[unresolved-import]: Cannot resolve imported module `package1`
+     --> test.py:4:6
+      |
+    2 | from package1 import ActiveVenv
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+      |      ^^^^^^^^
+    5 | from package1 import BaseConda
+      |
+    info: make sure your Python environment is properly configured: https://docs.astral.sh/ty/modules/#python-environment
+    info: rule `unresolved-import` is enabled by default
+
+    error[unresolved-import]: Cannot resolve imported module `package1`
+     --> test.py:5:6
+      |
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+    5 | from package1 import BaseConda
+      |      ^^^^^^^^
+      |
+    info: make sure your Python environment is properly configured: https://docs.astral.sh/ty/modules/#python-environment
+    info: rule `unresolved-import` is enabled by default
+
+    Found 4 diagnostics
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // Run with VIRTUAL_ENV set, should find the active venv
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("VIRTUAL_ENV", case.root().join("myvenv")), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `ActiveVenv`
+     --> test.py:2:22
+      |
+    2 | from package1 import ActiveVenv
+      |                      ^^^^^^^^^^
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // run with CONDA_PREFIX set, should find the child conda
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("CONDA_PREFIX", case.root().join("conda-env")), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `ChildConda`
+     --> test.py:3:22
+      |
+    2 | from package1 import ActiveVenv
+    3 | from package1 import ChildConda
+      |                      ^^^^^^^^^^
+    4 | from package1 import WorkingVenv
+    5 | from package1 import BaseConda
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // run with CONDA_PREFIX and CONDA_DEFAULT_ENV set (unequal), should find child conda
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("CONDA_PREFIX", case.root().join("conda-env"))
+        .env("CONDA_DEFAULT_ENV", "base"), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `ChildConda`
+     --> test.py:3:22
+      |
+    2 | from package1 import ActiveVenv
+    3 | from package1 import ChildConda
+      |                      ^^^^^^^^^^
+    4 | from package1 import WorkingVenv
+    5 | from package1 import BaseConda
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // run with CONDA_PREFIX and CONDA_DEFAULT_ENV (unequal) and VIRTUAL_ENV set,
+    // should find child active venv
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("CONDA_PREFIX", case.root().join("conda-env"))
+        .env("CONDA_DEFAULT_ENV", "base")
+        .env("VIRTUAL_ENV", case.root().join("myvenv")), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `ActiveVenv`
+     --> test.py:2:22
+      |
+    2 | from package1 import ActiveVenv
+      |                      ^^^^^^^^^^
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
+
+    ----- stderr -----
+    WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.
+    ");
+
+    // run with CONDA_PREFIX and CONDA_DEFAULT_ENV (equal!) set, should find base conda
+    assert_cmd_snapshot!(case.command()
+        .current_dir(case.root().join("project"))
+        .env("CONDA_PREFIX", case.root().join("conda/envs/base"))
+        .env("CONDA_DEFAULT_ENV", "base"), @r"
+    success: false
+    exit_code: 1
+    ----- stdout -----
+    error[unresolved-import]: Module `package1` has no member `BaseConda`
+     --> test.py:5:22
+      |
+    3 | from package1 import ChildConda
+    4 | from package1 import WorkingVenv
+    5 | from package1 import BaseConda
+      |                      ^^^^^^^^^
+      |
+    info: rule `unresolved-import` is enabled by default
+
+    Found 1 diagnostic
 
     ----- stderr -----
     WARN ty is pre-release software and not ready for production use. Expect to encounter bugs, missing features, and fatal errors.

crates/ty_python_semantic/src/site_packages.rs

@@ -139,6 +139,12 @@ pub enum PythonEnvironment {
 }
 
 impl PythonEnvironment {
+    /// Discover the python environment using the following priorities:
+    ///
+    /// 1. activated virtual environment
+    /// 2. conda (child)
+    /// 3. working dir virtual environment
+    /// 4. conda (base)
     pub fn discover(
         project_root: &SystemPath,
         system: &dyn System,
@@ -161,13 +167,9 @@ impl PythonEnvironment {
             .map(Some);
         }
 
-        if let Ok(conda_env) = system.env_var(EnvVars::CONDA_PREFIX) {
+        if let Some(conda_env) = conda_environment_from_env(system, CondaEnvironmentKind::Child) {
-            return resolve_environment(
+            return resolve_environment(system, &conda_env, SysPrefixPathOrigin::CondaPrefixVar)
-                system,
+                .map(Some);
-                SystemPath::new(&conda_env),
-                SysPrefixPathOrigin::CondaPrefixVar,
-            )
-            .map(Some);
         }
 
         tracing::debug!("Discovering virtual environment in `{project_root}`");
@@ -190,6 +192,11 @@ impl PythonEnvironment {
             }
         }
 
+        if let Some(conda_env) = conda_environment_from_env(system, CondaEnvironmentKind::Base) {
+            return resolve_environment(system, &conda_env, SysPrefixPathOrigin::CondaPrefixVar)
+                .map(Some);
+        }
+
         Ok(None)
     }
 
@@ -589,6 +596,62 @@ System stdlib will not be used for module definitions.",
     }
 }
 
+/// Different kinds of conda environment
+#[derive(Debug, PartialEq, Eq, Copy, Clone)]
+pub(crate) enum CondaEnvironmentKind {
+    /// The base Conda environment; treated like a system Python environment.
+    Base,
+    /// Any other Conda environment; treated like a virtual environment.
+    Child,
+}
+
+impl CondaEnvironmentKind {
+    /// Compute the kind of `CONDA_PREFIX` we have.
+    ///
+    /// 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>`.
+    fn from_prefix_path(system: &dyn System, path: &SystemPath) -> Self {
+        // If we cannot read `CONDA_DEFAULT_ENV`, there's no way to know if the base environment
+        let Ok(default_env) = system.env_var(EnvVars::CONDA_DEFAULT_ENV) else {
+            return CondaEnvironmentKind::Child;
+        };
+
+        // These are the expected names for the base environment
+        if default_env != "base" && default_env != "root" {
+            return CondaEnvironmentKind::Child;
+        }
+
+        let Some(name) = path.file_name() else {
+            return CondaEnvironmentKind::Child;
+        };
+
+        if name == default_env {
+            CondaEnvironmentKind::Base
+        } else {
+            CondaEnvironmentKind::Child
+        }
+    }
+}
+
+/// Read `CONDA_PREFIX` and confirm that it has the expected kind
+pub(crate) fn conda_environment_from_env(
+    system: &dyn System,
+    kind: CondaEnvironmentKind,
+) -> Option<SystemPathBuf> {
+    let dir = system
+        .env_var(EnvVars::CONDA_PREFIX)
+        .ok()
+        .filter(|value| !value.is_empty())?;
+    let path = SystemPathBuf::from(dir);
+
+    if kind != CondaEnvironmentKind::from_prefix_path(system, &path) {
+        return None;
+    }
+
+    Some(path)
+}
+
 /// A parser for `pyvenv.cfg` files: metadata files for virtual environments.
 ///
 /// Note that a `pyvenv.cfg` file *looks* like a `.ini` file, but actually isn't valid `.ini` syntax!

crates/ty_static/src/env_vars.rs

@@ -42,6 +42,9 @@ impl EnvVars {
     /// Used to detect an activated virtual environment.
     pub const VIRTUAL_ENV: &'static str = "VIRTUAL_ENV";
 
+    /// Used to determine if an active Conda environment is the base environment or not.
+    pub const CONDA_DEFAULT_ENV: &'static str = "CONDA_DEFAULT_ENV";
+
     /// Used to detect an activated Conda environment location.
     /// If both `VIRTUAL_ENV` and `CONDA_PREFIX` are present, `VIRTUAL_ENV` will be preferred.
     pub const CONDA_PREFIX: &'static str = "CONDA_PREFIX";