Improve display of selected interpreter sources (#3748)

e.g. this error message is not great

```
❯ uv venv --python 3.12.2
  × No interpreter found for Python 3.12.2 in provided path, search path, managed toolchains, or parent interpreter
```

crates/uv-interpreter/src/discovery.rs

@@ -44,9 +44,15 @@ pub enum InterpreterRequest {
 /// The sources to consider when finding a Python interpreter.
 #[derive(Debug, Clone, PartialEq, Eq, Default)]
 pub enum SourceSelector {
+    // Consider all interpreter sources.
     #[default]
     All,
-    Some(HashSet<InterpreterSource>),
+    // Only consider system interpreter sources
+    System,
+    // Only consider virtual environment sources
+    VirtualEnv,
+    // Only consider a custom set of sources
+    Custom(HashSet<InterpreterSource>),
 }
 
 /// A Python interpreter version request.
@@ -579,11 +585,7 @@ pub fn find_interpreter(
 /// See [`find_interpreter`] for more details on interpreter discovery.
 pub fn find_default_interpreter(cache: &Cache) -> Result<InterpreterResult, Error> {
     let request = InterpreterRequest::Version(VersionRequest::Default);
-    let sources = SourceSelector::from_sources([
+    let sources = SourceSelector::System;
-        InterpreterSource::SearchPath,
-        #[cfg(windows)]
-        InterpreterSource::PyLauncher,
-    ]);
 
     let result = find_interpreter(&request, SystemPython::Required, &sources, cache)?;
     if let Ok(ref found) = result {
@@ -612,7 +614,7 @@ pub fn find_best_interpreter(
     debug!("Starting interpreter discovery for {}", request);
 
     // Determine if we should be allowed to look outside of virtual environments.
-    let sources = SourceSelector::from_env(system);
+    let sources = SourceSelector::from_settings(system);
 
     // First, check for an exact match (or the first available version if no Python versfion was provided)
     debug!("Looking for exact match for request {request}");
@@ -1079,19 +1081,33 @@ impl SourceSelector {
     pub(crate) fn from_sources(iter: impl IntoIterator<Item = InterpreterSource>) -> Self {
         let inner = HashSet::from_iter(iter);
         assert!(!inner.is_empty(), "Source selectors cannot be empty");
-        Self::Some(inner)
+        Self::Custom(inner)
     }
 
     /// Return true if this selector includes the given [`InterpreterSource`].
     fn contains(&self, source: InterpreterSource) -> bool {
         match self {
             Self::All => true,
-            Self::Some(sources) => sources.contains(&source),
+            Self::System => [
+                InterpreterSource::ProvidedPath,
+                InterpreterSource::SearchPath,
+                #[cfg(windows)]
+                InterpreterSource::PyLauncher,
+                InterpreterSource::ManagedToolchain,
+                InterpreterSource::ParentInterpreter,
+            ]
+            .contains(&source),
+            Self::VirtualEnv => [
+                InterpreterSource::DiscoveredEnvironment,
+                InterpreterSource::ActiveEnvironment,
+            ]
+            .contains(&source),
+            Self::Custom(sources) => sources.contains(&source),
         }
     }
 
-    /// Return the default [`SourceSelector`] based on environment variables.
+    /// Return a [`SourceSelector`] based the settings.
-    pub fn from_env(system: SystemPython) -> Self {
+    pub fn from_settings(system: SystemPython) -> Self {
         if env::var_os("UV_FORCE_MANAGED_PYTHON").is_some() {
             debug!("Only considering managed toolchains due to `UV_FORCE_MANAGED_PYTHON`");
             Self::from_sources([InterpreterSource::ManagedToolchain])
@@ -1106,18 +1122,8 @@ impl SourceSelector {
         } else {
             match system {
                 SystemPython::Allowed | SystemPython::Explicit => Self::All,
-                SystemPython::Required => Self::from_sources([
+                SystemPython::Required => Self::System,
-                    InterpreterSource::ProvidedPath,
+                SystemPython::Disallowed => Self::VirtualEnv,
-                    InterpreterSource::SearchPath,
-                    #[cfg(windows)]
-                    InterpreterSource::PyLauncher,
-                    InterpreterSource::ManagedToolchain,
-                    InterpreterSource::ParentInterpreter,
-                ]),
-                SystemPython::Disallowed => Self::from_sources([
-                    InterpreterSource::DiscoveredEnvironment,
-                    InterpreterSource::ActiveEnvironment,
-                ]),
             }
         }
     }
@@ -1232,7 +1238,21 @@ impl fmt::Display for SourceSelector {
     fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
         match self {
             Self::All => f.write_str("all sources"),
-            Self::Some(sources) => {
+            Self::VirtualEnv => f.write_str("virtual environments"),
+            Self::System => {
+                // TODO(zanieb): We intentionally omit managed toolchains for now since they are not public
+                if cfg!(windows) {
+                    write!(
+                        f,
+                        "{} or {}",
+                        InterpreterSource::SearchPath,
+                        InterpreterSource::PyLauncher
+                    )
+                } else {
+                    write!(f, "{}", InterpreterSource::SearchPath)
+                }
+            }
+            Self::Custom(sources) => {
                 let sources: Vec<_> = sources
                     .iter()
                     .sorted()

crates/uv-interpreter/src/environment.rs

@@ -51,10 +51,7 @@ impl PythonEnvironment {
 
     /// Create a [`PythonEnvironment`] for an existing virtual environment.
     pub fn from_virtualenv(cache: &Cache) -> Result<Self, Error> {
-        let sources = SourceSelector::from_sources([
+        let sources = SourceSelector::VirtualEnv;
-            InterpreterSource::DiscoveredEnvironment,
-            InterpreterSource::ActiveEnvironment,
-        ]);
         let request = InterpreterRequest::Version(VersionRequest::Default);
         let found = find_interpreter(&request, SystemPython::Disallowed, &sources, cache)??;
 
@@ -109,7 +106,7 @@ impl PythonEnvironment {
         system: SystemPython,
         cache: &Cache,
     ) -> Result<Self, Error> {
-        let sources = SourceSelector::from_env(system);
+        let sources = SourceSelector::from_settings(system);
         let request = InterpreterRequest::parse(request);
         let interpreter = find_interpreter(&request, system, &sources, cache)??.into_interpreter();
         Ok(Self(Arc::new(PythonEnvironmentShared {

crates/uv-interpreter/src/lib.rs

@@ -700,12 +700,7 @@ mod tests {
     fn find_interpreter_version_minor() -> Result<()> {
         let tempdir = TempDir::new()?;
         let cache = Cache::temp()?;
-        let sources = SourceSelector::from_sources([
+        let sources = SourceSelector::All;
-            InterpreterSource::ProvidedPath,
-            InterpreterSource::ActiveEnvironment,
-            InterpreterSource::DiscoveredEnvironment,
-            InterpreterSource::SearchPath,
-        ]);
 
         with_vars(
             [
@@ -757,12 +752,7 @@ mod tests {
     fn find_interpreter_version_patch() -> Result<()> {
         let tempdir = TempDir::new()?;
         let cache = Cache::temp()?;
-        let sources = SourceSelector::from_sources([
+        let sources = SourceSelector::All;
-            InterpreterSource::ProvidedPath,
-            InterpreterSource::ActiveEnvironment,
-            InterpreterSource::DiscoveredEnvironment,
-            InterpreterSource::SearchPath,
-        ]);
 
         with_vars(
             [
@@ -814,12 +804,7 @@ mod tests {
     fn find_interpreter_version_minor_no_match() -> Result<()> {
         let tempdir = TempDir::new()?;
         let cache = Cache::temp()?;
-        let sources = SourceSelector::from_sources([
+        let sources = SourceSelector::All;
-            InterpreterSource::ProvidedPath,
-            InterpreterSource::ActiveEnvironment,
-            InterpreterSource::DiscoveredEnvironment,
-            InterpreterSource::SearchPath,
-        ]);
 
         with_vars(
             [
@@ -861,12 +846,7 @@ mod tests {
     fn find_interpreter_version_patch_no_match() -> Result<()> {
         let tempdir = TempDir::new()?;
         let cache = Cache::temp()?;
-        let sources = SourceSelector::from_sources([
+        let sources = SourceSelector::All;
-            InterpreterSource::ProvidedPath,
-            InterpreterSource::ActiveEnvironment,
-            InterpreterSource::DiscoveredEnvironment,
-            InterpreterSource::SearchPath,
-        ]);
 
         with_vars(
             [

crates/uv/src/commands/pip/compile.rs

@@ -170,7 +170,7 @@ pub(crate) async fn pip_compile(
     };
     let interpreter = if let Some(python) = python.as_ref() {
         let request = InterpreterRequest::parse(python);
-        let sources = SourceSelector::from_env(system);
+        let sources = SourceSelector::from_settings(system);
         find_interpreter(&request, system, &sources, &cache)??
     } else {
         let request = if let Some(version) = python_version.as_ref() {

crates/uv/src/commands/venv.rs

@@ -121,7 +121,7 @@ async fn venv_impl(
     let interpreter = if let Some(python) = python_request.as_ref() {
         let system = uv_interpreter::SystemPython::Required;
         let request = InterpreterRequest::parse(python);
-        let sources = SourceSelector::from_env(system);
+        let sources = SourceSelector::from_settings(system);
         find_interpreter(&request, system, &sources, cache)
     } else {
         find_default_interpreter(cache)

crates/uv/tests/venv.rs

@@ -218,20 +218,33 @@ fn create_venv_unknown_python_minor() {
     let mut command = context.venv_command();
     command
         .arg(context.venv.as_os_str())
+        // Request a version we know we'll never see
         .arg("--python")
-        .arg("3.15");
+        .arg("3.100")
+        // Unset this variable to force what the user would see
+        .env_remove("UV_TEST_PYTHON_PATH");
 
-    // Note the `py` launcher is not included in the search in Windows due to
+    if cfg!(windows) {
-    // `UV_TEST_PYTHON_PATH` being set
         uv_snapshot!(&mut command, @r###"
         success: false
         exit_code: 1
         ----- stdout -----
 
         ----- stderr -----
-      × No interpreter found for Python 3.15 in active virtual environment or search path
+          × No interpreter found for Python 3.100 in search path or `py` launcher output
         "###
         );
+    } else {
+        uv_snapshot!(&mut command, @r###"
+        success: false
+        exit_code: 1
+        ----- stdout -----
+
+        ----- stderr -----
+          × No interpreter found for Python 3.100 in search path
+        "###
+        );
+    }
 
     context.venv.assert(predicates::path::missing());
 }
@@ -240,18 +253,36 @@ fn create_venv_unknown_python_minor() {
 fn create_venv_unknown_python_patch() {
     let context = VenvTestContext::new(&["3.12"]);
 
-    uv_snapshot!(context.filters(), context.venv_command()
+    let mut command = context.venv_command();
+    command
         .arg(context.venv.as_os_str())
+        // Request a version we know we'll never see
         .arg("--python")
-        .arg("3.8.0"), @r###"
+        .arg("3.12.100")
+        // Unset this variable to force what the user would see
+        .env_remove("UV_TEST_PYTHON_PATH");
+
+    if cfg!(windows) {
+        uv_snapshot!(&mut command, @r###"
         success: false
         exit_code: 1
         ----- stdout -----
 
         ----- stderr -----
-      × No interpreter found for Python 3.8.0 in active virtual environment or search path
+          × No interpreter found for Python 3.12.100 in search path or `py` launcher output
         "###
         );
+    } else {
+        uv_snapshot!(&mut command, @r###"
+        success: false
+        exit_code: 1
+        ----- stdout -----
+
+        ----- stderr -----
+          × No interpreter found for Python 3.12.100 in search path
+        "###
+        );
+    }
 
     context.venv.assert(predicates::path::missing());
 }