Add color to python pin CLI (#5215)

## Summary

![Screenshot 2024-07-19 at 9 03
10 AM](https://github.com/user-attachments/assets/5668bd23-3f09-4964-bc09-9f3788f5a841)

crates/uv-python/src/lib.rs

@@ -14,10 +14,11 @@ pub use crate::prefix::Prefix;
 pub use crate::python_version::PythonVersion;
 pub use crate::target::Target;
 pub use crate::version_files::{
-    request_from_version_file, requests_from_version_file, PYTHON_VERSIONS_FILENAME,
+    request_from_version_file, requests_from_version_file, write_version_file,
-    PYTHON_VERSION_FILENAME,
+    PYTHON_VERSIONS_FILENAME, PYTHON_VERSION_FILENAME,
 };
 pub use crate::virtualenv::{Error as VirtualEnvError, PyVenvConfiguration, VirtualEnvironment};
+
 mod discovery;
 pub mod downloads;
 mod environment;
@@ -83,19 +84,19 @@ pub enum Error {
 // TODO(zanieb): We should write a mock interpreter script that works on Windows
 #[cfg(all(test, unix))]
 mod tests {
-    use anyhow::Result;
-    use indoc::{formatdoc, indoc};
-
     use std::{
         env,
         ffi::{OsStr, OsString},
         path::{Path, PathBuf},
         str::FromStr,
     };
+
+    use anyhow::Result;
+    use assert_fs::{fixture::ChildPath, prelude::*, TempDir};
+    use indoc::{formatdoc, indoc};
     use temp_env::with_vars;
     use test_log::test;
 
-    use assert_fs::{fixture::ChildPath, prelude::*, TempDir};
     use uv_cache::Cache;
 
     use crate::{

crates/uv-python/src/version_files.rs

@@ -46,6 +46,12 @@ pub async fn request_from_version_file() -> Result<Option<PythonRequest>, std::i
     }
 }
 
+/// Write a version to a .`python-version` file.
+pub async fn write_version_file(version: &str) -> Result<(), std::io::Error> {
+    debug!("Writing Python version `{version}` to `{PYTHON_VERSION_FILENAME}`");
+    fs::tokio::write(PYTHON_VERSION_FILENAME, format!("{version}\n")).await
+}
+
 async fn read_versions_file() -> Result<Option<Vec<String>>, std::io::Error> {
     match fs::tokio::read_to_string(PYTHON_VERSIONS_FILENAME).await {
         Ok(content) => {

crates/uv/src/commands/python/pin.rs

@@ -1,15 +1,15 @@
 use std::fmt::Write;
-use std::path::PathBuf;
 
 use anyhow::{bail, Result};
+use owo_colors::OwoColorize;
 
-use tracing::debug;
 use uv_cache::Cache;
 use uv_configuration::PreviewMode;
 use uv_fs::Simplified;
 use uv_python::{
-    requests_from_version_file, EnvironmentPreference, PythonInstallation, PythonPreference,
+    request_from_version_file, requests_from_version_file, write_version_file,
-    PythonRequest, PYTHON_VERSION_FILENAME,
+    EnvironmentPreference, PythonInstallation, PythonPreference, PythonRequest,
+    PYTHON_VERSION_FILENAME,
 };
 use uv_warnings::warn_user_once;
 
@@ -50,7 +50,7 @@ pub(crate) async fn pin(
         Ok(python) => Some(python),
         // If no matching Python version is found, don't fail unless `resolved` was requested
         Err(uv_python::Error::MissingPython(err)) if !resolved => {
-            warn_user_once!("{}", err);
+            warn_user_once!("{err}");
             None
         }
         Err(err) => return Err(err.into()),
@@ -68,16 +68,27 @@ pub(crate) async fn pin(
         request.to_canonical_string()
     };
 
-    debug!("Using pin `{}`", output);
+    let existing = request_from_version_file().await.ok().flatten();
-    let version_file = PathBuf::from(PYTHON_VERSION_FILENAME);
+    write_version_file(&output).await?;
-    let exists = version_file.exists();
 
-    debug!("Writing pin to {}", version_file.user_display());
+    if let Some(existing) = existing
-    fs_err::write(&version_file, format!("{output}\n"))?;
+        .map(|existing| existing.to_canonical_string())
-    if exists {
+        .filter(|existing| existing != &output)
-        writeln!(printer.stdout(), "Replaced existing pin with `{output}`")?;
+    {
+        writeln!(
+            printer.stdout(),
+            "Updated `{}` from `{}` -> `{}`",
+            PYTHON_VERSION_FILENAME.cyan(),
+            existing.green(),
+            output.green()
+        )?;
     } else {
-        writeln!(printer.stdout(), "Pinned to `{output}`")?;
+        writeln!(
+            printer.stdout(),
+            "Pinned `{}` to `{}`",
+            PYTHON_VERSION_FILENAME.cyan(),
+            output.green()
+        )?;
     }
 
     Ok(ExitStatus::Success)

crates/uv/tests/python_pin.rs

@@ -28,7 +28,7 @@ fn python_pin() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Pinned to `any`
+    Pinned `.python-version` to `any`
 
     ----- stderr -----
     "###);
@@ -57,7 +57,7 @@ fn python_pin() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `3.12`
+    Updated `.python-version` from `any` -> `3.12`
 
     ----- stderr -----
     "###);
@@ -73,7 +73,7 @@ fn python_pin() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `3.11`
+    Updated `.python-version` from `3.12` -> `3.11`
 
     ----- stderr -----
     "###);
@@ -89,7 +89,7 @@ fn python_pin() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `cpython`
+    Updated `.python-version` from `3.11` -> `cpython`
 
     ----- stderr -----
     "###);
@@ -105,7 +105,7 @@ fn python_pin() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `cpython@3.12`
+    Updated `.python-version` from `cpython` -> `cpython@3.12`
 
     ----- stderr -----
     "###);
@@ -121,7 +121,7 @@ fn python_pin() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `cpython@3.12`
+    Pinned `.python-version` to `cpython@3.12`
 
     ----- stderr -----
     "###);
@@ -137,7 +137,7 @@ fn python_pin() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `cpython-3.12-any-any-any`
+    Updated `.python-version` from `cpython@3.12` -> `cpython-3.12-any-any-any`
 
     ----- stderr -----
     "###);
@@ -153,7 +153,7 @@ fn python_pin() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `[PYTHON-3.11]`
+    Updated `.python-version` from `cpython-3.12-any-any-any` -> `[PYTHON-3.11]`
 
     ----- stderr -----
     "###);
@@ -176,7 +176,7 @@ fn python_pin() {
         success: true
         exit_code: 0
         ----- stdout -----
-        Replaced existing pin with `pypy`
+        Updated `.python-version` from `[PYTHON-3.11]` -> `pypy`
 
         ----- stderr -----
         warning: No interpreter found for PyPy in system path
@@ -194,14 +194,14 @@ fn python_pin() {
     #[cfg(unix)]
     {
         uv_snapshot!(context.filters(), context.python_pin().arg("3.7"), @r###"
-    success: true
+        success: true
-    exit_code: 0
+        exit_code: 0
-    ----- stdout -----
+        ----- stdout -----
-    Replaced existing pin with `3.7`
+        Updated `.python-version` from `pypy` -> `3.7`
 
-    ----- stderr -----
+        ----- stderr -----
-    warning: No interpreter found for Python 3.7 in system path
+        warning: No interpreter found for Python 3.7 in system path
-    "###);
+        "###);
 
         let python_version =
             fs_err::read_to_string(context.temp_dir.join(PYTHON_VERSION_FILENAME)).unwrap();
@@ -222,7 +222,7 @@ fn python_pin_no_python() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Pinned to `3.12`
+    Pinned `.python-version` to `3.12`
 
     ----- stderr -----
     warning: No interpreter found for Python 3.12 in system path
@@ -264,7 +264,7 @@ fn python_pin_resolve() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Pinned to `[PYTHON-3.11]`
+    Pinned `.python-version` to `[PYTHON-3.11]`
 
     ----- stderr -----
     "###);
@@ -284,7 +284,7 @@ fn python_pin_resolve() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `[PYTHON-3.12]`
+    Updated `.python-version` from `[PYTHON-3.11]` -> `[PYTHON-3.12]`
 
     ----- stderr -----
     "###);
@@ -304,7 +304,7 @@ fn python_pin_resolve() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `[PYTHON-3.11]`
+    Updated `.python-version` from `[PYTHON-3.12]` -> `[PYTHON-3.11]`
 
     ----- stderr -----
     "###);
@@ -324,7 +324,7 @@ fn python_pin_resolve() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `[PYTHON-3.11]`
+    Pinned `.python-version` to `[PYTHON-3.11]`
 
     ----- stderr -----
     "###);
@@ -344,7 +344,7 @@ fn python_pin_resolve() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `[PYTHON-3.12]`
+    Updated `.python-version` from `[PYTHON-3.11]` -> `[PYTHON-3.12]`
 
     ----- stderr -----
     "###);
@@ -364,7 +364,7 @@ fn python_pin_resolve() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `[PYTHON-3.12]`
+    Pinned `.python-version` to `[PYTHON-3.12]`
 
     ----- stderr -----
     "###);
@@ -389,7 +389,7 @@ fn python_pin_resolve() {
     success: true
     exit_code: 0
     ----- stdout -----
-    Replaced existing pin with `[PYTHON-3.12]`
+    Pinned `.python-version` to `[PYTHON-3.12]`
 
     ----- stderr -----
     "###);