Fix hygiene violations in some warnings

Pull request #37 added some must_use warnings conditionalized on the
"nightly" feature.  However, because proc macros are unhygienic, the
warnings were actually conditionalized on the instantiating crate's
nightly feature, not on mockall_derive's nightly feature.  I didn't
notice at the time because Mockall _also_ has a nightly feature, and so
does the only crate of mine that uses Mockall.

Fix the hygiene errors, and rename mockall_derive's feature to
"nightly_derive", which will help to catch similar errors in the future.

CHANGELOG.md

@@ -8,6 +8,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 ### Fixed
 
+- Fixed hygiene violations in some of mockall_derive's warnings.
+  ([#63](https://github.com/asomers/mockall/pull/63))
+
 - Fixed using super:: in the signature of a bare function
   ([#54](https://github.com/asomers/mockall/pull/54))
 

mockall/Cargo.toml

@@ -18,7 +18,7 @@ features = ["nightly"]
 
 [features]
 # Extra features for the nightly compiler only
-nightly = ["mockall_derive/nightly"]
+nightly = ["mockall_derive/nightly_derive"]
 
 [dependencies]
 cfg-if = "0.1.6"

mockall_derive/Cargo.toml

@@ -20,7 +20,9 @@ proc-macro = true
 
 [features]
 # Extra features for the nightly compiler only
-nightly = ["proc-macro2/nightly"]
+# Must have a different name than the corresponding feature in mockall in order
+# to catch hygiene violations.
+nightly_derive = ["proc-macro2/nightly"]
 # For building documentation only; no functional change to the library.
 extra-docs = []
 

mockall_derive/src/expectation.rs

@@ -1051,6 +1051,13 @@ impl<'a> StaticExpectation<'a> {
             )
         };
 
+        #[cfg(not(feature = "nightly_derive"))]
+        let must_use = quote!(#[must_use =
+                "Must set return value when not using the \"nightly\" feature"
+            ]);
+        #[cfg(feature = "nightly_derive")]
+        let must_use = quote!();
+
         let context_ts = quote!(
             /// Manages the context for expectations of static methods.
             ///
@@ -1083,9 +1090,7 @@ impl<'a> StaticExpectation<'a> {
                 }
 
                 /// Create a new expectation for this method.
-                #[cfg_attr(not(feature = "nightly"), must_use =
-                    "Must set return value when not using the \"nightly\" feature")
-                ]
+                #must_use
                 #v fn expect #meth_ig ( &self,) -> ExpectationGuard #e_tg
                     #meth_wc
                 {
@@ -1588,6 +1593,14 @@ impl<'a> RefExpectation<'a> {
         let (ig, tg, wc) = self.common.egenerics.split_for_impl();
         let lg = &self.common.elifetimes;
         let output = &self.common.output;
+
+        #[cfg(not(feature = "nightly_derive"))]
+        let default_err_msg =
+            "Returning default values requires the \"nightly\" feature";
+        #[cfg(feature = "nightly_derive")]
+        let default_err_msg =
+            "Can only return default values for types that impl std::Default";
+
         quote!(
             enum Rfunc #ig #wc {
                 Default(Option<#output>),
@@ -1604,13 +1617,8 @@ impl<'a> RefExpectation<'a> {
                         Rfunc::Default(Some(ref __mockall_o)) => {
                             Ok(__mockall_o)
                         },
-                        #[cfg(feature = "nightly")]
-                        Rfunc::Default(None) => {
-                            Err("Can only return default values for types that impl std::Default")
-                        },
-                        #[cfg(not(feature = "nightly"))]
                         Rfunc::Default(None) => {
-                            Err("Returning default values requires the \"nightly\" feature")
+                            Err(#default_err_msg)
                         },
                         Rfunc::Const(ref __mockall_o) => {
                             Ok(__mockall_o)
@@ -1809,6 +1817,14 @@ impl<'a> RefMutExpectation<'a> {
         let (ig, tg, wc) = self.common.egenerics.split_for_impl();
         let lg = &self.common.elifetimes;
         let output = &self.common.output;
+
+        #[cfg(not(feature = "nightly_derive"))]
+        let default_err_msg =
+            "Returning default values requires the \"nightly\" feature";
+        #[cfg(feature = "nightly_derive")]
+        let default_err_msg =
+            "Can only return default values for types that impl std::Default";
+
         quote!(
             enum Rfunc #ig #wc {
                 Default(Option<#output>),
@@ -1834,13 +1850,8 @@ impl<'a> RefMutExpectation<'a> {
                         Rfunc::Default(Some(ref mut __mockall_o)) => {
                             Ok(__mockall_o)
                         },
-                        #[cfg(feature = "nightly")]
-                        Rfunc::Default(None) => {
-                            Err("Can only return default values for types that impl std::Default")
-                        },
-                        #[cfg(not(feature = "nightly"))]
                         Rfunc::Default(None) => {
-                            Err("Returning default values requires the \"nightly\" feature")
+                            Err(#default_err_msg)
                         },
                         Rfunc::Mut(ref mut __mockall_f, ref mut __mockall_o) =>
                         {

mockall_derive/src/lib.rs

@@ -5,7 +5,7 @@
 //! its reexports via the [`mockall`](https://docs.rs/mockall/latest/mockall)
 //! crate.
 
-#![cfg_attr(feature = "nightly", feature(proc_macro_diagnostic))]
+#![cfg_attr(feature = "nightly_derive", feature(proc_macro_diagnostic))]
 extern crate proc_macro;
 
 use cfg_if::cfg_if;
@@ -62,7 +62,7 @@ cfg_if! {
     // proc-macro2's Span::unstable method requires the nightly feature, and it
     // doesn't work in test mode.
     // https://github.com/alexcrichton/proc-macro2/issues/159
-    if #[cfg(all(feature = "nightly", not(test)))] {
+    if #[cfg(all(feature = "nightly_derive", not(test)))] {
         fn compile_error(span: Span, msg: &'static str) {
             span.unstable()
                 .error(msg)

mockall_derive/src/mock.rs

@@ -314,10 +314,16 @@ fn gen_mock_method(mock_struct_name: &syn::Ident,
         #[cfg(any(test, not(feature = "extra-docs")))]
         let docstr: Option<syn::Attribute> = None;
         let expect_ident = format_ident!("expect_{}", ident);
+
+        #[cfg(not(feature = "nightly_derive"))]
+        let must_use = quote!(#[must_use =
+                "Must set return value when not using the \"nightly\" feature"
+            ]);
+        #[cfg(feature = "nightly_derive")]
+        let must_use = quote!();
+
         quote!(
-            #[cfg_attr(not(feature = "nightly"), must_use =
-                "Must set return value when not using the \"nightly\" feature")
-            ]
+            #must_use
             #attrs #docstr #expect_vis fn #expect_ident #ig(&mut self)
                -> &mut #mod_ident::#expectation
                #wc