Add #[tracing::instrument] compatibility for #[automock]

The mock method won't be instrumented, but at least it will compile.

Fixes #253

CHANGELOG.md

@@ -22,6 +22,10 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Fixed Clippy warnings in generated code with Rustc 1.52.0.
   ([#255](https://github.com/asomers/mockall/pull/255))
 
+- Fixed using `#[automock]` with `#[tracing::instrument]`.  The mock function
+  won't be instrumented, but at least it will compile.
+  ([#256](https://github.com/asomers/mockall/pull/256))
+
 ### Removed
 
 ## [0.9.0] - 2020-12-21

mockall/Cargo.toml

@@ -49,6 +49,7 @@ mockall_double = { version = "^0.2.0", path = "../mockall_double" }
 serde = "1.0"
 serde_derive = "1.0"
 serde_json = "1.0"
+tracing = "0.1.23"
 
 [[example]]
 name = "serde"

mockall/tests/automock_instrument.rs

@@ -0,0 +1,22 @@
+// vim: tw=80
+//! A trait that uses tracing::instrument should be automockable.  The mock
+//! method won't be instrumented, though.
+#![deny(warnings)]
+
+use mockall::*;
+use tracing::instrument;
+
+#[derive(Debug)]
+pub struct Foo {}
+
+#[automock]
+impl Foo {
+    #[instrument]
+    fn foo(&self) {}
+    #[instrument]
+    fn bar() {}
+    #[tracing::instrument]
+    fn fooz(&self) {}
+    #[tracing::instrument]
+    fn barz() {}
+}

mockall_derive/src/lib.rs

@@ -549,20 +549,27 @@ impl<'a> AttrFormatter<'a> {
 
     // XXX This logic requires that attributes are imported with their
     // standard names.
+    #[allow(clippy::needless_bool)]
     fn format(&mut self) -> Vec<Attribute> {
         self.attrs.iter()
             .cloned()
-            .filter(|attr|
-                ( self.doc ||
-                    attr.path.get_ident()
-                    .map(|i| i != "doc")
-                    .unwrap_or(false)
-                ) && (self.async_trait ||
-                    attr.path.get_ident()
-                    .map(|i| i != "async_trait")
-                    .unwrap_or(false)
-                )
-            ).collect()
+            .filter(|attr| {
+                let i = attr.path.get_ident();
+                if i.is_none() {
+                    false
+                } else if *i.as_ref().unwrap() == "doc" {
+                    self.doc
+                } else if *i.as_ref().unwrap() == "async_trait" {
+                    self.async_trait
+                } else if *i.as_ref().unwrap() == "instrument" {
+                    // We can't usefully instrument the mock method, so just
+                    // ignore this attribute.
+                    // https://docs.rs/tracing/0.1.23/tracing/attr.instrument.html
+                    false
+                } else {
+                    true
+                }
+            }).collect()
     }
 }