Refuse to remove non-virtual environments in `uv venv` (#15538)

## Summary

Closes https://github.com/astral-sh/uv/issues/15474.

crates/uv-virtualenv/src/virtualenv.rs

@@ -110,7 +110,8 @@ pub(crate) fn create(
             );
         }
         Ok(metadata) if metadata.is_dir() => {
-            let name = if uv_fs::is_virtualenv_base(location) {
+            let is_virtualenv = uv_fs::is_virtualenv_base(location);
+            let name = if is_virtualenv {
                 "virtual environment"
             } else {
                 "directory"
@@ -131,7 +132,14 @@ pub(crate) fn create(
                     fs::create_dir_all(&location)?;
                 }
                 OnExisting::Fail => {
-                    match confirm_clear(location, name)? {
+                    let confirmation = if is_virtualenv {
+                        confirm_clear(location, name)?
+                    } else {
+                        // Refuse to remove a non-virtual environment; don't even prompt.
+                        Some(false)
+                    };
+
+                    match confirmation {
                         Some(true) => {
                             debug!("Removing existing {name} due to confirmation");
                             // Before removing the virtual environment, we need to canonicalize the

crates/uv/tests/it/venv.rs

@@ -958,7 +958,8 @@ fn empty_dir_exists() -> Result<()> {
 fn non_empty_dir_exists() -> Result<()> {
     let context = TestContext::new_with_versions(&["3.12"]);
 
-    // Create a non-empty directory at `.venv`. Creating a virtualenv at the same path should fail.
+    // Create a non-empty directory at `.venv`. Creating a virtualenv at the same path should fail,
+    // unless `--clear` is specified.
     context.venv.create_dir_all()?;
     context.venv.child("file").touch()?;
 
@@ -966,6 +967,25 @@ fn non_empty_dir_exists() -> Result<()> {
         .arg(context.venv.as_os_str())
         .arg("--python")
         .arg("3.12"), @r"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
+    Creating virtual environment at: .venv
+    error: Failed to create virtual environment
+      Caused by: A directory already exists at: .venv
+
+    hint: Use the `--clear` flag or set `UV_VENV_CLEAR=1` to replace the existing directory
+    "
+    );
+
+    uv_snapshot!(context.filters(), context.venv()
+        .arg(context.venv.as_os_str())
+        .arg("--clear")
+        .arg("--python")
+        .arg("3.12"), @r"
     success: true
     exit_code: 0
     ----- stdout -----
@@ -973,7 +993,6 @@ fn non_empty_dir_exists() -> Result<()> {
     ----- stderr -----
     Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
     Creating virtual environment at: .venv
-    warning: A directory already exists at `.venv`. In the future, uv will require `--clear` to replace it
     Activate with: source .venv/[BIN]/activate
     "
     );
@@ -994,15 +1013,17 @@ fn non_empty_dir_exists_allow_existing() -> Result<()> {
         .arg(context.venv.as_os_str())
         .arg("--python")
         .arg("3.12"), @r"
-    success: true
+    success: false
-    exit_code: 0
+    exit_code: 2
     ----- stdout -----
 
     ----- stderr -----
     Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
     Creating virtual environment at: .venv
-    warning: A directory already exists at `.venv`. In the future, uv will require `--clear` to replace it
+    error: Failed to create virtual environment
-    Activate with: source .venv/[BIN]/activate
+      Caused by: A directory already exists at: .venv
+
+    hint: Use the `--clear` flag or set `UV_VENV_CLEAR=1` to replace the existing directory
     "
     );
 
@@ -1578,17 +1599,33 @@ fn create_venv_current_working_directory() {
     let context = TestContext::new_with_versions(&["3.12"]);
 
     uv_snapshot!(context.filters(), context.venv()
-        .arg(".")
+        .arg(context.venv.as_os_str())
         .arg("--python")
         .arg("3.12"), @r"
     success: true
     exit_code: 0
     ----- stdout -----
 
+    ----- stderr -----
+    Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
+    Creating virtual environment at: .venv
+    Activate with: source .venv/[BIN]/activate
+    "
+    );
+
+    uv_snapshot!(context.filters(), context.venv()
+        .arg(".")
+        .arg("--clear")
+        .arg("--python")
+        .arg("3.12")
+        .current_dir(&context.venv), @r"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
     ----- stderr -----
     Using CPython 3.12.[X] interpreter at: [PYTHON-3.12]
     Creating virtual environment at: .
-    warning: A directory already exists at `.`. In the future, uv will require `--clear` to replace it
     Activate with: source bin/activate
     "
     );