check subcommand should force rebuild

src/bin/cargo/commands/check.rs

@@ -27,6 +27,7 @@ pub fn cli() -> App {
             "Check all targets",
         )
         .arg_release("Check artifacts in release mode, with optimizations")
+        .arg_force_rebuild("Force rebuild of the selected target(s)")
         .arg(opt("profile", "Profile to build the selected target for").value_name("PROFILE"))
         .arg_features()
         .arg_target_triple("Check for the target triple")

src/cargo/util/command_prelude.rs

@@ -185,6 +185,10 @@ pub trait AppExt: Sized {
     fn arg_dry_run(self, dry_run: &'static str) -> Self {
         self._arg(opt("dry-run", dry_run))
     }
+
+    fn arg_force_rebuild(self, force_rebuild: &'static str) -> Self {
+        self._arg(opt("force-rebuild", force_rebuild))
+    }
 }
 
 impl AppExt for App {
@@ -362,6 +366,12 @@ pub trait ArgMatchesExt {
         let mut build_config = BuildConfig::new(config, self.jobs()?, &self.target(), mode)?;
         build_config.message_format = message_format.unwrap_or(MessageFormat::Human);
         build_config.release = self._is_present("release");
+        build_config.force_rebuild = self._is_present("force-rebuild");
+        if build_config.force_rebuild && !config.cli_unstable().unstable_options {
+            Err(failure::format_err!(
+                "`--force-rebuild` flag is unstable, pass `-Z unstable-options` to enable it"
+            ))?;
+        };
         build_config.build_plan = self._is_present("build-plan");
         if build_config.build_plan {
             config

tests/testsuite/check.rs

@@ -194,6 +194,32 @@ fn build_check() {
     foo.cargo("check -v").run();
 }
 
+// Checks that --force-rebuild displays warnings even if the project has not changed
+//     since the last check/build
+#[test]
+fn force_rebuild_displays_error() {
+    let foo = project()
+        .file(
+            "src/main.rs",
+            "use std::default::Default; fn main() {}",
+        )
+        .build();
+
+    foo.cargo("check")
+        .with_stderr_contains("[..]warning: unused import[..]")
+        .run();
+
+    // for now this requires the unstable feature flag, so expect an error here
+    let output = foo.cargo("check --force-rebuild")
+        .exec_with_output();
+    assert!(output.is_err());
+
+    foo.cargo("check -Z unstable-options --force-rebuild")
+        .masquerade_as_nightly_cargo() // remove this when `-Z unstable-options` is no longer required
+        .with_stderr_contains("[..]warning: unused import[..]")
+        .run();
+}
+
 // Checks that where a project has both a lib and a bin, the lib is only checked
 // not built.
 #[cargo_test]