Error if all is combined with other targets

src/cli/errors.rs

@@ -49,5 +49,12 @@ error_chain! {
             description("completion script for shell not yet supported for tool")
             display("{} does not currently support completions for {}", cmd, shell)
         }
+        TargetAllSpecifiedWithTargets(t: Vec<String>) {
+            description(
+                "the `all` target, which installs all available targets, \
+                 cannot be combined with other targets"
+            )
+            display("`rustup target add {}` includes `all`", t.join(" "))
+        }
     }
 }

src/cli/rustup_mode.rs

@@ -866,6 +866,10 @@ fn target_add(cfg: &Cfg, m: &ArgMatches<'_>) -> Result<()> {
         .collect();
 
     if targets.contains(&"all".to_string()) {
+        if targets.len() != 1 {
+            return Err(ErrorKind::TargetAllSpecifiedWithTargets(targets).into());
+        }
+
         targets.clear();
         for component in toolchain.list_components()? {
             if component.component.short_name_in_manifest() == "rust-std"

tests/cli-v2.rs

@@ -602,6 +602,29 @@ fn add_all_targets() {
     });
 }
 
+#[test]
+fn add_all_targets_fail() {
+    setup(&|config| {
+        expect_ok(config, &["rustup", "default", "nightly"]);
+        expect_err(
+            config,
+            &[
+                "rustup",
+                "target",
+                "add",
+                clitools::CROSS_ARCH1,
+                "all",
+                clitools::CROSS_ARCH2,
+            ],
+            format!(
+                "`rustup target add {} all {}` includes `all`",
+                clitools::CROSS_ARCH1,
+                clitools::CROSS_ARCH2
+            ),
+        );
+    });
+}
+
 #[test]
 fn add_target_no_toolchain() {
     setup(&|config| {