Add some must_use warnings

CHANGELOG.md

@@ -6,6 +6,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ## [Unreleased] - ReleaseDate
 ### Added
 
+- Warnings for misued expectations and context objects
+  ([#37](https://github.com/asomers/mockall/pull/37))
+
 - Methods with closure arguments and where clauses can now be mocked.
   ([#35](https://github.com/asomers/mockall/pull/35))
 

mockall/tests/mock_generic_struct_with_generic_static_method.rs

@@ -60,6 +60,7 @@ fn ctx_hygiene() {
 }
 
 #[cfg_attr(not(feature = "nightly"), ignore)]
+#[cfg_attr(not(feature = "nightly"), allow(unused_must_use))]
 #[test]
 fn return_default() {
     let _m = BAR_MTX.lock();

mockall/tests/mock_generic_struct_with_nondefault_parameter.rs

@@ -20,6 +20,7 @@ mock! {
 #[should_panic(expected =
     "Can only return default values for types that impl std::Default")]
 #[cfg_attr(not(feature = "nightly"), ignore)]
+#[cfg_attr(not(feature = "nightly"), allow(unused_must_use))]
 fn return_default() {
     let mut mock = MockExternalStruct::<NonDefault>::new();
     mock.expect_foo();

mockall/tests/mock_return_mutable_reference.rs

@@ -12,6 +12,7 @@ mock! {
 #[test]
 #[cfg_attr(not(feature = "nightly"),
            should_panic(expected = "Returning default values requires"))]
+#[cfg_attr(not(feature = "nightly"), allow(unused_must_use))]
 fn return_default() {
     let mut mock = MockFoo::new();
     mock.expect_foo();

mockall/tests/mock_return_reference.rs

@@ -43,6 +43,7 @@ fn return_const() {
 #[test]
 #[cfg_attr(not(feature = "nightly"),
            should_panic(expected = "Returning default values requires"))]
+#[cfg_attr(not(feature = "nightly"), allow(unused_must_use))]
 fn return_default() {
     let mut mock = MockFoo::new();
     mock.expect_foo();

mockall/tests/mock_struct.rs

@@ -188,6 +188,7 @@ fn return_const() {
 
 #[cfg_attr(not(feature = "nightly"),
            should_panic(expected = "Returning default values requires"))]
+#[cfg_attr(not(feature = "nightly"), allow(unused_must_use))]
 #[test]
 fn return_default() {
     let mut mock = MockFoo::new();

mockall/tests/mock_struct_with_static_method.rs

@@ -59,6 +59,7 @@ fn ctx_hygiene() {
 }
 
 #[cfg_attr(not(feature = "nightly"), ignore)]
+#[cfg_attr(not(feature = "nightly"), allow(unused_must_use))]
 #[test]
 fn return_default() {
     let _m = BAR_MTX.lock();

mockall_derive/src/expectation.rs

@@ -949,6 +949,7 @@ impl<'a> StaticExpectation<'a> {
         };
 
         let context_ts = quote!(
+            #[must_use = "Context only serves to create expectations" ]
             #v struct Context #s_ig #s_wc {
                 // Prevent "unused type parameter" errors
                 // Surprisingly, PhantomData<Fn(generics)> is Send even if
@@ -970,6 +971,9 @@ impl<'a> StaticExpectation<'a> {
                         .collect::<Vec<_>>();
                 }
 
+                #[cfg_attr(not(feature = "nightly"), must_use =
+                    "Must set return value when not using the \"nightly\" feature")
+                ]
                 #v fn expect #meth_ig ( &self,) -> ExpectationGuard #e_tg
                     #meth_wc
                 {

mockall_derive/src/mock.rs

@@ -305,12 +305,17 @@ fn gen_mock_method(mod_ident: Option<&syn::Ident>,
         #[cfg(any(test, not(feature = "extra-docs")))]
         let docstr: Option<syn::Attribute> = None;
         let expect_ident = format_ident!("expect_{}", ident);
-        quote!(#attrs #docstr #expect_vis fn #expect_ident #ig(&mut self)
+        quote!(
+            #[cfg_attr(not(feature = "nightly"), must_use =
+                "Must set return value when not using the \"nightly\" feature")
+            ]
+            #attrs #docstr #expect_vis fn #expect_ident #ig(&mut self)
                -> &mut #mod_ident::#expectation
                #wc
-        {
-            #expect_obj_name.expect#call_turbofish()
-        })
+            {
+                #expect_obj_name.expect#call_turbofish()
+            }
+        )
     }.to_tokens(&mut expect_output);
 
     // Finally this method's contribution to the checkpoint method