add --skip-modify-path to rye self install

This adds the option to never modify paths to rye install, even when
`--yes` is provided. This addresses #620.

Notable we chose to not require "--yes" for this to work, so you can
have an install with prompt and still skip path.

rye/src/cli/rye.rs

@@ -96,6 +96,9 @@ pub struct InstallCommand {
     /// Use a specific toolchain version.
     #[arg(long)]
     toolchain_version: Option<PythonVersionRequest>,
+    /// Skip modifying the PATH environment variable.
+    #[arg(long, default_value = "false")]
+    skip_modify_path: bool,
 }
 
 #[derive(Debug, Copy, Clone)]
@@ -263,6 +266,7 @@ fn install(args: InstallCommand) -> Result<(), Error> {
         },
         args.toolchain.as_deref(),
         args.toolchain_version,
+        args.skip_modify_path,
     )
 }
 
@@ -351,6 +355,7 @@ fn perform_install(
     mode: InstallMode,
     toolchain_path: Option<&Path>,
     toolchain_version: Option<PythonVersionRequest>,
+    skip_modify_path: bool,
 ) -> Result<(), Error> {
     let mut config = Config::current();
     let mut registered_toolchain: Option<PythonVersionRequest> = None;
@@ -547,7 +552,14 @@ fn perform_install(
         prompt_for_default_toolchain(registered_toolchain.unwrap(), config_doc)?;
     }
 
-    add_rye_to_path(&mode, shims.as_path())?;
+    if skip_modify_path {
+        echo!(
+            "Skipping PATH modification. You will need to add {} to your PATH manually.",
+            style(shims.display()).cyan()
+        );
+    } else {
+        add_rye_to_path(&mode, shims.as_path())?;
+    }
 
     echo!();
     echo!("{}", style("All done!").green());
@@ -670,7 +682,7 @@ pub fn auto_self_install() -> Result<bool, Error> {
             crate::request_continue_prompt();
         }
 
-        perform_install(InstallMode::AutoInstall, None, None)?;
+        perform_install(InstallMode::AutoInstall, None, None, false)?;
         Ok(true)
     }
 }