Implement warning for ignored trailing arguments

in case built-in `cargo` command was invoked with `--`

src/bin/cargo/cli.rs

@@ -1,6 +1,7 @@
 use cargo::core::{features, CliUnstable};
 use cargo::{self, drop_print, drop_println, CliResult, Config};
 use clap::{AppSettings, Arg, ArgMatches};
+use itertools::Itertools;
 
 use super::commands;
 use super::list_commands;
@@ -169,6 +170,17 @@ fn expand_aliases(
                     cmd,
                 ))?;
             }
+            (Some(_), None) => {
+                // Command is built-in and is not conflicting with alias, but contains ignored values.
+                if let Some(mut values) = args.values_of("") {
+                    config.shell().warn(format!(
+                        "trailing arguments after built-in command `{}` are ignored: `{}`",
+                        cmd,
+                        values.join(" "),
+                    ))?;
+                }
+            }
+            (None, None) => {}
             (_, Some(mut alias)) => {
                 alias.extend(
                     args.values_of("")
@@ -186,7 +198,6 @@ fn expand_aliases(
                 let (expanded_args, _) = expand_aliases(config, new_args)?;
                 return Ok((expanded_args, global_args));
             }
-            (_, None) => {}
         }
     };
 

tests/testsuite/cargo_alias_config.rs

@@ -192,3 +192,21 @@ fn global_options_with_alias() {
         )
         .run();
 }
+
+#[cargo_test]
+fn weird_check() {
+    let p = project()
+        .file("Cargo.toml", &basic_bin_manifest("foo"))
+        .file("src/main.rs", "fn main() {}")
+        .build();
+
+    p.cargo("-- check --invalid_argument -some-other-argument")
+        .with_stderr(
+            "\
+[WARNING] trailing arguments after built-in command `check` are ignored: `--invalid_argument -some-other-argument`
+[CHECKING] foo v0.5.0 ([..])
+[FINISHED] dev [unoptimized + debuginfo] target(s) in [..]
+",
+        )
+        .run();
+}