From 3810964e1483e75e35dd3d7731bfb22887709b43 Mon Sep 17 00:00:00 2001
From: rami3l <rami3l@outlook.com>
Date: Mon, 15 Jan 2024 14:59:14 +0800
Subject: [PATCH] feat(cli): warn when removing the last/host target for a
 toolchain

---
 Cargo.lock             | 12 +++++++++++-
 Cargo.toml             |  1 +
 src/cli/rustup_mode.rs | 23 ++++++++++++++++++-----
 tests/suite/cli_v2.rs  | 26 ++++++++++++++++++++++++--
 4 files changed, 54 insertions(+), 8 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 1704235812..46c7d43ad2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1074,6 +1074,15 @@ dependencies = [
  "either",
 ]
 
+[[package]]
+name = "itertools"
+version = "0.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "25db6b064527c5d482d0423354fcd07a89a2dfe07b67892e62411946db7f07b0"
+dependencies = [
+ "either",
+]
+
 [[package]]
 name = "itoa"
 version = "1.0.10"
@@ -1566,7 +1575,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e5d2d8d10f3c6ded6da8b05b5fb3b8a5082514344d56c9f871412d29b4e075b4"
 dependencies = [
  "anyhow",
- "itertools",
+ "itertools 0.10.5",
  "proc-macro2",
  "quote",
  "syn 1.0.109",
@@ -1887,6 +1896,7 @@ dependencies = [
  "fs_at",
  "git-testament",
  "home",
+ "itertools 0.12.0",
  "libc",
  "once_cell",
  "opener",
diff --git a/Cargo.toml b/Cargo.toml
index 2a84c608d2..1d4cf9b4e0 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -57,6 +57,7 @@ flate2 = "1"
 fs_at.workspace = true
 git-testament = "0.2"
 home = "0.5.4"
+itertools = "0.12"
 libc = "0.2"
 once_cell.workspace = true
 opener = "0.6.0"
diff --git a/src/cli/rustup_mode.rs b/src/cli/rustup_mode.rs
index 8281e77ebe..189899561c 100644
--- a/src/cli/rustup_mode.rs
+++ b/src/cli/rustup_mode.rs
@@ -10,6 +10,7 @@ use clap::{
     Arg, ArgAction, ArgGroup, ArgMatches, Command, ValueEnum,
 };
 use clap_complete::Shell;
+use itertools::Itertools;
 
 use crate::{
     cli::{
@@ -1334,11 +1335,23 @@ fn target_remove(cfg: &Cfg, m: &ArgMatches) -> Result<utils::ExitCode> {
     let distributable = DistributableToolchain::try_from(&toolchain)?;
 
     for target in m.get_many::<String>("target").unwrap() {
-        let new_component = Component::new(
-            "rust-std".to_string(),
-            Some(TargetTriple::new(target)),
-            false,
-        );
+        let target = TargetTriple::new(target);
+        let default_target = cfg.get_default_host_triple()?;
+        if target == default_target {
+            warn!("after removing the default host target, proc-macros and build scripts might no longer build");
+        }
+        let has_at_most_one_target = {
+            let components = distributable.components()?;
+            // Every component target that is not `None` (wildcard).
+            let targets = components
+                .iter()
+                .filter_map(|c| c.installed.then(|| c.component.target.clone()).flatten());
+            targets.unique().at_most_one().is_ok()
+        };
+        if has_at_most_one_target {
+            warn!("after removing the last target, no build targets will be available");
+        }
+        let new_component = Component::new("rust-std".to_string(), Some(target), false);
         distributable.remove_component(new_component)?;
     }
 
diff --git a/tests/suite/cli_v2.rs b/tests/suite/cli_v2.rs
index 563e6609fc..81ba41e75d 100644
--- a/tests/suite/cli_v2.rs
+++ b/tests/suite/cli_v2.rs
@@ -952,9 +952,31 @@ fn remove_target_again() {
 #[test]
 fn remove_target_host() {
     setup(&|config| {
-        let trip = this_host_triple();
+        let host = this_host_triple();
         config.expect_ok(&["rustup", "default", "nightly"]);
-        config.expect_ok(&["rustup", "target", "remove", &trip]);
+        config.expect_ok(&["rustup", "target", "add", clitools::CROSS_ARCH1]);
+        config.expect_stderr_ok(
+            &["rustup", "target", "remove", &host], 
+            "after removing the default host target, proc-macros and build scripts might no longer build",
+        );
+        let path = format!("toolchains/nightly-{host}/lib/rustlib/{host}/lib/libstd.rlib");
+        assert!(!config.rustupdir.has(path));
+        let path = format!("toolchains/nightly-{host}/lib/rustlib/{host}/lib");
+        assert!(!config.rustupdir.has(path));
+        let path = format!("toolchains/nightly-{host}/lib/rustlib/{host}");
+        assert!(!config.rustupdir.has(path));
+    });
+}
+
+#[test]
+fn remove_target_last() {
+    setup(&|config| {
+        let host = this_host_triple();
+        config.expect_ok(&["rustup", "default", "nightly"]);
+        config.expect_stderr_ok(
+            &["rustup", "target", "remove", &host],
+            "after removing the last target, no build targets will be available",
+        );
     });
 }