Automatically install Python version needed for tool

crates/uv/src/commands/tool/install.rs

@@ -25,12 +25,12 @@ use crate::commands::pip::loggers::{DefaultInstallLogger, DefaultResolveLogger};
 
 use crate::commands::project::{
     resolve_environment, resolve_names, sync_environment, update_environment,
-    EnvironmentSpecification,
+    EnvironmentSpecification, ProjectError,
 };
 use crate::commands::tool::common::remove_entrypoints;
 use crate::commands::tool::Target;
+use crate::commands::{pip, ExitStatus, SharedState};
 use crate::commands::{reporters::PythonDownloadReporter, tool::common::install_executables};
-use crate::commands::{ExitStatus, SharedState};
 use crate::printer::Printer;
 use crate::settings::ResolverInstallerSettings;
 
@@ -328,12 +328,13 @@ pub(crate) async fn install(
     }
 
     // Create a `RequirementsSpecification` from the resolved requirements, to avoid re-resolving.
+    let spec_requirements: Vec<UnresolvedRequirementSpecification> = requirements
+        .iter()
+        .cloned()
+        .map(UnresolvedRequirementSpecification::from)
+        .collect();
     let spec = RequirementsSpecification {
-        requirements: requirements
-            .iter()
-            .cloned()
-            .map(UnresolvedRequirementSpecification::from)
-            .collect(),
+        requirements: spec_requirements.clone(),
         ..spec
     };
 
@@ -380,7 +381,52 @@ pub(crate) async fn install(
             &cache,
             printer,
         )
-        .await?;
+        .await;
+
+        let resolution = match resolution {
+            Ok(resolution) => resolution,
+            Err(
+                err @ ProjectError::Operation(pip::operations::Error::Resolve(
+                    uv_resolver::ResolveError::NoSolution(_),
+                )),
+            ) => {
+                if python_request.is_some() {
+                    return Err(err.into());
+                }
+
+                let interpreter = PythonInstallation::find_or_download(
+                    Some(&PythonRequest::parse("3.12")),
+                    EnvironmentPreference::OnlySystem,
+                    python_preference,
+                    python_downloads,
+                    &client_builder,
+                    &cache,
+                    Some(&reporter),
+                )
+                .await?
+                .into_interpreter();
+
+                let new_spec = RequirementsSpecification {
+                    requirements: spec_requirements,
+                    ..RequirementsSpecification::default()
+                };
+
+                resolve_environment(
+                    EnvironmentSpecification::from(new_spec),
+                    &interpreter,
+                    settings.as_ref().into(),
+                    &state,
+                    Box::new(DefaultResolveLogger),
+                    connectivity,
+                    concurrency,
+                    native_tls,
+                    &cache,
+                    printer,
+                )
+                .await?
+            }
+            Err(e) => return Err(e.into()),
+        };
 
         let environment = installed_tools.create_environment(&from.name, interpreter)?;
 

crates/uv/tests/tool_install.rs

@@ -3007,3 +3007,25 @@ fn tool_install_at_latest_upgrade() {
         "###);
     });
 }
+
+#[test]
+fn tool_install_python() {
+    let context = TestContext::new("3.8");
+    let tool_dir = context.temp_dir.child("tools");
+    let bin_dir = context.temp_dir.child("bin");
+
+    uv_snapshot!(context.filters(), context.tool_install()
+        .arg("posting")
+        .arg("--python")
+        .arg("3.8")
+        .env("UV_TOOL_DIR", tool_dir.as_os_str())
+        .env("XDG_BIN_HOME", bin_dir.as_os_str())
+        .env("PATH", bin_dir.as_os_str()), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+
+    "###);
+}