Automatically generate Debug impls for mock structs

Fixes #287

CHANGELOG.md

@@ -7,6 +7,11 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
+- automock will now automatically generate Debug implementations for traits and
+  structs.  mock! will to, if you put `#[derive(Debug)]` above the struct's
+  name.
+  ([#289](https://github.com/asomers/mockall/pull/289))
+
 - Added support for specific impls.  A specific impl is an implementation of a
   trait on a generic struct with specified generic parameters.  For example,
   `impl Foo for Bar<i32>` as opposed to `impl<T> Foo for Bar<T>`.  Mockall does

mockall/src/lib.rs

@@ -45,6 +45,7 @@
 //! * [`Static methods`](#static-methods)
 //! * [`Modules`](#modules)
 //! * [`Foreign functions`](#foreign-functions)
+//! * [`Debug`](#debug)
 //! * [`Async Traits`](#async-traits)
 //! * [`Crate features`](#crate-features)
 //! * [`Examples`](#examples)
@@ -1032,6 +1033,22 @@
 //! # fn main() {}
 //! ```
 //!
+//! ## Debug
+//!
+//! `#[automock]` will automatically generate `Debug` impls when mocking traits
+//! and struct impls.  `mock!` will too, if you add a `#[derive(Debug)]`, like
+//! this:
+//! ```no_run
+//! # use mockall::*;
+//! mock! {
+//!     #[derive(Debug)]
+//!     pub Foo {}
+//! }
+//! # fn main() {
+//! #     format!("{:?}", &MockFoo::default());
+//! # }
+//! ```
+//!
 //! ## Async Traits
 //!
 //! Async traits aren't yet (as of 1.47.0) a part of the Rust language.  But

mockall/tests/automock_debug.rs

@@ -0,0 +1,35 @@
+// vim: tw=80
+//! A mocked struct should implement Debug
+#![deny(warnings)]
+
+use mockall::*;
+
+#[automock]
+pub trait Foo {}
+
+pub trait Bar {}
+pub struct Baz {}
+#[automock]
+impl Bar for Baz{}
+
+pub struct Bean {}
+#[automock]
+impl Bean{}
+
+#[test]
+fn automock_trait() {
+    let foo = MockFoo::new();
+    assert_eq!("MockFoo", format!("{:?}", foo));
+}
+
+#[test]
+fn automock_struct_impl() {
+    let bean = MockBean::new();
+    assert_eq!("MockBean", format!("{:?}", bean));
+}
+
+#[test]
+fn automock_trait_impl() {
+    let baz = MockBaz::new();
+    assert_eq!("MockBaz", format!("{:?}", baz));
+}

mockall/tests/mock_debug.rs

@@ -0,0 +1,44 @@
+// vim: tw=80
+//! A mocked struct should implement Debug
+#![deny(warnings)]
+
+use mockall::*;
+use std::fmt::{self, Debug, Formatter};
+
+// using derive(Debug) tells mockall to generate the Debug impl automatically
+mock!{
+    #[derive(Debug)]
+    pub Bar {
+        fn foo(&self) -> u32;
+    }
+    impl Clone for Bar {
+        fn clone(&self) -> Self;
+    }
+}
+
+// With no derive(Debug), mockall won't genetate the debug impl automatically
+mock!{
+    pub Baz {
+        fn foo(&self) -> u32;
+    }
+    impl Clone for Baz {
+        fn clone(&self) -> Self;
+    }
+}
+impl Debug for MockBaz {
+    fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), fmt::Error> {
+        f.debug_struct("XXX").finish()
+    }
+}
+
+#[test]
+fn automatic() {
+    let bar = MockBar::new();
+    assert_eq!("MockBar", format!("{:?}", bar));
+}
+
+#[test]
+fn manual() {
+    let baz = MockBaz::new();
+    assert_eq!("XXX", format!("{:?}", baz));
+}

mockall_derive/src/lib.rs

@@ -572,6 +572,9 @@ impl<'a> AttrFormatter<'a> {
                 let i = attr.path.get_ident();
                 if i.is_none() {
                     false
+                } else if *i.as_ref().unwrap() == "derive" {
+                    // We can't usefully derive any traits.  Ignore them
+                    false
                 } else if *i.as_ref().unwrap() == "doc" {
                     self.doc
                 } else if *i.as_ref().unwrap() == "async_trait" {

mockall_derive/src/mock_item_struct.rs

@@ -116,6 +116,8 @@ pub(crate) struct MockItemStruct {
     attrs: Vec<Attribute>,
     consts: Vec<ImplItemConst>,
     generics: Generics,
+    /// Should Mockall generate a Debug implementation?
+    auto_debug: bool,
     /// Does the original struct have a `new` method?
     has_new: bool,
     /// Inherent methods of the mock struct
@@ -129,6 +131,25 @@ pub(crate) struct MockItemStruct {
 }
 
 impl MockItemStruct {
+    fn debug_impl(&self) -> impl ToTokens {
+        if self.auto_debug {
+            let (ig, tg, wc) = self.generics.split_for_impl();
+            let struct_name = &self.name;
+            let struct_name_str = format!("{}", self.name);
+            quote!(
+                impl #ig ::std::fmt::Debug for #struct_name #tg #wc {
+                    fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>)
+                        -> ::std::result::Result<(), std::fmt::Error>
+                    {
+                        f.debug_struct(#struct_name_str).finish()
+                    }
+                }
+            )
+        } else {
+            quote!()
+        }
+    }
+
     fn new_method(&self) -> impl ToTokens {
         if self.has_new {
             TokenStream::new()
@@ -159,6 +180,7 @@ impl MockItemStruct {
 
 impl From<MockableStruct> for MockItemStruct {
     fn from(mockable: MockableStruct) -> MockItemStruct {
+        let auto_debug = mockable.derives_debug();
         let modname = gen_mod_ident(&mockable.name, None);
         let generics = mockable.generics.clone();
         let struct_name = &mockable.name;
@@ -192,6 +214,7 @@ impl From<MockableStruct> for MockItemStruct {
 
         MockItemStruct {
             attrs: mockable.attrs,
+            auto_debug,
             consts: mockable.consts,
             generics,
             has_new,
@@ -210,6 +233,7 @@ impl ToTokens for MockItemStruct {
             .async_trait(false)
             .format();
         let consts = &self.consts;
+        let debug_impl = self.debug_impl();
         let struct_name = &self.name;
         let (ig, tg, wc) = self.generics.split_for_impl();
         let modname = &self.modname;
@@ -283,6 +307,7 @@ impl ToTokens for MockItemStruct {
             {
                 #(#field_definitions),*
             }
+            #debug_impl
             impl #ig ::std::default::Default for #struct_name #tg #wc {
                 #[allow(clippy::default_trait_access)]
                 fn default() -> Self {

mockall_derive/src/mockable_struct.rs

@@ -92,6 +92,17 @@ fn add_lifetime_parameters(sig: &mut Signature) {
     }
 }
 
+/// Generate a #[derive(Debug)] Attribute
+fn derive_debug() -> Attribute {
+    Attribute {
+        pound_token: <Token![#]>::default(),
+        style: AttrStyle::Outer,
+        bracket_token: token::Bracket::default(),
+        path: Path::from(format_ident!("derive")),
+        tokens: quote!((Debug))
+    }
+}
+
 /// Add "Mock" to the front of the named type
 fn mock_ident_in_type(ty: &mut Type) {
     match ty {
@@ -291,10 +302,38 @@ pub(crate) struct MockableStruct {
     pub impls: Vec<ItemImpl>
 }
 
+impl MockableStruct {
+    /// Does this struct derive Debug?
+    pub fn derives_debug(&self) -> bool {
+        self.attrs.iter()
+        .any(|attr| {
+            if let Ok(Meta::List(ml)) = attr.parse_meta() {
+                let i = ml.path.get_ident();
+                if i.map_or(false, |i| *i == "derive") {
+                    ml.nested.iter()
+                    .any(|nm| {
+                        if let NestedMeta::Meta(m) = nm {
+                            let i = m.path().get_ident();
+                            i.map_or(false, |i| *i == "Debug")
+                        } else {
+                            false
+                        }
+                    })
+                } else {
+                    false
+                }
+            } else {
+                false
+            }
+        })
+    }
+}
+
 impl From<(Attrs, ItemTrait)> for MockableStruct {
     fn from((attrs, item_trait): (Attrs, ItemTrait)) -> MockableStruct {
         let trait_ = attrs.substitute_trait(&item_trait);
-        let attrs = trait_.attrs.clone();
+        let mut attrs = trait_.attrs.clone();
+        attrs.push(derive_debug());
         let vis = trait_.vis.clone();
         let name = gen_mock_ident(&trait_.ident);
         let generics = trait_.generics.clone();
@@ -324,7 +363,8 @@ impl From<ItemImpl> for MockableStruct {
                 Ident::new("", Span::call_site())
             }
         };
-        let attrs = item_impl.attrs.clone();
+        let mut attrs = item_impl.attrs.clone();
+        attrs.push(derive_debug());
         let mut consts = Vec::new();
         let generics = item_impl.generics.clone();
         let mut methods = Vec::new();