feat(rustup-init): detect and warn about existing settings.toml

src/cli/self_update.rs

@@ -512,6 +512,7 @@ pub(crate) async fn install(
         .map_or(false, |s| s == "yes")
     {
         check_existence_of_rustc_or_cargo_in_path(no_prompt, process)?;
+        check_existence_of_settings_file(process)?;
     }
 
     #[cfg(unix)]
@@ -631,7 +632,7 @@ fn check_existence_of_rustc_or_cargo_in_path(no_prompt: bool, process: &Process)
     }
 
     if let Err(path) = rustc_or_cargo_exists_in_path(process) {
-        warn!("it looks like you have an existing installation of Rust at:");
+        warn!("It looks like you have an existing installation of Rust at:");
         warn!("{}", path);
         warn!("It is recommended that rustup be the primary Rust installation.");
         warn!("Otherwise you may have confusion unless you are careful with your PATH.");
@@ -643,6 +644,18 @@ fn check_existence_of_rustc_or_cargo_in_path(no_prompt: bool, process: &Process)
     Ok(())
 }
 
+fn check_existence_of_settings_file(process: &Process) -> Result<()> {
+    let rustup_dir = process.rustup_home()?;
+    let settings_file_path = rustup_dir.join("settings.toml");
+    if utils::path_exists(&settings_file_path) {
+        warn!("It looks like you have an existing rustup settings file at:");
+        warn!("{}", settings_file_path.display());
+        warn!("Rustup will install the default toolchain as specified in the settings file,");
+        warn!("instead of the one inferred from the default host triple.");
+    }
+    Ok(())
+}
+
 fn pre_install_msg(no_modify_path: bool, process: &Process) -> Result<String> {
     let cargo_home = process.cargo_home()?;
     let cargo_home_bin = cargo_home.join("bin");

tests/suite/cli_inst_interactive.rs

@@ -498,7 +498,7 @@ async fn install_stops_if_rustc_exists() {
     assert!(!out.ok);
     assert!(out
         .stderr
-        .contains("it looks like you have an existing installation of Rust at:"));
+        .contains("It looks like you have an existing installation of Rust at:"));
     assert!(out
         .stderr
         .contains("If you are sure that you want both rustup and your already installed Rust"));
@@ -530,7 +530,7 @@ async fn install_stops_if_cargo_exists() {
     assert!(!out.ok);
     assert!(out
         .stderr
-        .contains("it looks like you have an existing installation of Rust at:"));
+        .contains("It looks like you have an existing installation of Rust at:"));
     assert!(out
         .stderr
         .contains("If you are sure that you want both rustup and your already installed Rust"));
@@ -579,3 +579,40 @@ async fn install_non_installable_toolchain() {
         )
         .await;
 }
+
+#[tokio::test]
+async fn install_warns_about_existing_settings_file() {
+    let temp_dir = tempfile::Builder::new()
+        .prefix("fakehome")
+        .tempdir()
+        .unwrap();
+    // Create `settings.toml`
+    let settings_file = temp_dir.path().join("settings.toml");
+    raw::write_file(
+        &settings_file,
+        for_host!(
+            r#"default_toolchain = "{}"
+profile = "default"
+version = "12""#
+        ),
+    )
+    .unwrap();
+    let temp_dir_path = temp_dir.path().to_str().unwrap();
+
+    let cx = CliTestContext::new(Scenario::SimpleV2).await;
+    let out = cx
+        .config
+        .run(
+            "rustup-init",
+            ["-y", "--no-modify-path"],
+            &[
+                ("RUSTUP_INIT_SKIP_PATH_CHECK", "no"),
+                ("RUSTUP_HOME", temp_dir_path),
+            ],
+        )
+        .await;
+    assert!(out.ok);
+    assert!(out
+        .stderr
+        .contains("It looks like you have an existing rustup settings file at:"));
+}