Add support for global, non venv Python invocations

CHANGELOG.md

@@ -7,7 +7,11 @@ that were not yet released.
 
 _Unreleased_
 
-<!-- released start -->
+- Added support for the new `behavior.global-python` flag which turns on global
+  Python shimming.  When enabled then the `python` shim works even outside of
+  Rye managed projects.  Additionally the shim (when run outside of Rye managed
+  projects) supports a special first paramter `+VERSION` which requests a
+  specific version of Python (eg: `python +3.8` to request Python 3.8).  #336
 
 ## 0.8.0
 

docs/guide/config.md

@@ -72,6 +72,9 @@ https = "http://127.0.0.1:4000"
 # When set to true the `managed` flag is always assumed to be true.
 force_rye_managed = false
 
+# Enables global shims when set to `true`
+global-python = false
+
 # a array of tables with optional sources.  Same format as in pyproject.toml
 [[sources]]
 name = "default"

rye/src/cli/shim.rs

@@ -1,15 +1,19 @@
 use std::convert::Infallible;
 use std::env;
 use std::ffi::{OsStr, OsString};
+use std::str::FromStr;
 
-use anyhow::{bail, Context, Error};
+use anyhow::{anyhow, bail, Context, Error};
 use same_file::is_same_file;
 use std::process::Command;
 use which::which_in_global;
 
 use crate::bootstrap::{ensure_self_venv, get_pip_runner};
+use crate::config::Config;
 use crate::consts::VENV_BIN;
-use crate::pyproject::PyProject;
+use crate::platform::{get_python_version_request_from_pyenv_pin, get_toolchain_python_bin};
+use crate::pyproject::{latest_available_python_version, PyProject};
+use crate::sources::{PythonVersion, PythonVersionRequest};
 use crate::sync::{sync, SyncOptions};
 use crate::utils::{exec_spawn, get_venv_python_bin, CommandOutput};
 
@@ -101,6 +105,47 @@ fn get_shim_target(target: &str, args: &[OsString]) -> Result<Option<Vec<OsStrin
         if target == "pip" || target == "pip3" {
             return Ok(Some(get_pip_shim(&pyproject, args, CommandOutput::Normal)?));
         }
+    } else if target == "python" || target == "python3" {
+        let config = Config::current();
+        if config.global_python() {
+            let mut args = args.to_vec();
+            let mut remove1 = false;
+
+            let version_request = if let Some(rest) = args
+                .get(1)
+                .and_then(|x| x.as_os_str().to_str())
+                .and_then(|x| x.strip_prefix('+'))
+            {
+                remove1 = true;
+                PythonVersionRequest::from_str(rest)
+                    .context("invalid python version requested from command line")?
+            } else {
+                match get_python_version_request_from_pyenv_pin(&std::env::current_exe()?) {
+                    Some(version_request) => version_request,
+                    None => config.default_toolchain()?,
+                }
+            };
+
+            let py_ver = match PythonVersion::try_from(version_request.clone()) {
+                Ok(py_ver) => py_ver,
+                Err(_) => latest_available_python_version(&version_request)
+                    .ok_or_else(|| anyhow!("Unable to determine target Python version"))?,
+            };
+            let py = get_toolchain_python_bin(&py_ver)?;
+            if !py.is_file() {
+                bail!(
+                    "Requested Python version ({}) is not installed. Install with `rye fetch {}`",
+                    py_ver,
+                    py_ver
+                );
+            }
+
+            args[0] = py.into();
+            if remove1 {
+                args.remove(1);
+            }
+            return Ok(Some(args));
+        }
     }
 
     // if we make it this far, we did not find a shim in the project, look for

rye/src/config.rs

@@ -126,6 +126,15 @@ impl Config {
             })
     }
 
+    /// Allow rye shims to resolve globally installed Pythons.
+    pub fn global_python(&self) -> bool {
+        self.doc
+            .get("behavior")
+            .and_then(|x| x.get("global-python"))
+            .and_then(|x| x.as_bool())
+            .unwrap_or(false)
+    }
+
     /// Pretend that all projects are rye managed.
     pub fn force_rye_managed(&self) -> bool {
         self.doc