Automatically use StrComparison for comparing strings

pretty_assertions/src/lib.rs

@@ -242,13 +242,14 @@ macro_rules! assert_eq {
         match (&($left), &($right)) {
             (left_val, right_val) => {
                 if !(*left_val == *right_val) {
+                    use $crate::private::CreateComparison;
                     ::core::panic!("assertion failed: `(left == right)`{}{}\
                        \n\
                        \n{}\
                        \n",
                        $maybe_colon,
                        format_args!($($arg)*),
-                       $crate::Comparison::new(left_val, right_val)
+                       (left_val, right_val).create_comparison()
                     )
                 }
             }
@@ -430,3 +431,38 @@ macro_rules! assert_matches {
         }
     });
 }
+
+// Not public API. Used by the expansion of this crate's assert macros.
+#[doc(hidden)]
+pub mod private {
+    #[cfg(feature = "alloc")]
+    use alloc::string::String;
+
+    pub trait CompareAsStrByDefault: AsRef<str> {}
+    impl CompareAsStrByDefault for str {}
+    impl CompareAsStrByDefault for String {}
+    impl<T: CompareAsStrByDefault + ?Sized> CompareAsStrByDefault for &T {}
+
+    pub trait CreateComparison {
+        type Comparison;
+        fn create_comparison(self) -> Self::Comparison;
+    }
+
+    impl<'a, T, U> CreateComparison for &'a (T, U) {
+        type Comparison = crate::Comparison<'a, T, U>;
+        fn create_comparison(self) -> Self::Comparison {
+            crate::Comparison::new(&self.0, &self.1)
+        }
+    }
+
+    impl<'a, T, U> CreateComparison for (&'a T, &'a U)
+    where
+        T: CompareAsStrByDefault + ?Sized,
+        U: CompareAsStrByDefault + ?Sized,
+    {
+        type Comparison = crate::StrComparison<'a, T, U>;
+        fn create_comparison(self) -> Self::Comparison {
+            crate::StrComparison::new(self.0, self.1)
+        }
+    }
+}

pretty_assertions/tests/macros.rs

@@ -32,23 +32,23 @@ mod assert_str_eq {
         ::pretty_assertions::assert_str_eq!(s0, s1);
     }
 
-    #[test]
-    fn passes_as_ref_types() {
-        #[derive(PartialEq)]
-        struct MyString(String);
+    #[derive(PartialEq)]
+    struct MyString(String);
 
-        impl AsRef<str> for MyString {
-            fn as_ref(&self) -> &str {
-                &self.0
-            }
+    impl AsRef<str> for MyString {
+        fn as_ref(&self) -> &str {
+            &self.0
         }
+    }
 
-        impl PartialEq<String> for MyString {
-            fn eq(&self, other: &String) -> bool {
-                &self.0 == other
-            }
+    impl PartialEq<String> for MyString {
+        fn eq(&self, other: &String) -> bool {
+            &self.0 == other
         }
+    }
 
+    #[test]
+    fn passes_as_ref_types() {
         let s0 = MyString("foo".to_string());
         let s1 = "foo".to_string();
         ::pretty_assertions::assert_str_eq!(s0, s1);
@@ -62,6 +62,21 @@ mod assert_str_eq {
 <bar
 >baz
 
+"#)]
+    fn fails_as_ref_types() {
+        let s0 = MyString("foo\nbar".to_string());
+        let s1 = "foo\nbaz".to_string();
+        ::pretty_assertions::assert_str_eq!(s0, s1);
+    }
+
+    #[test]
+    #[should_panic(expected = r#"assertion failed: `(left == right)`
+
+Diff < left / right > :
+ foo
+<bar
+>baz
+
 "#)]
     fn fails_foo() {
         ::pretty_assertions::assert_str_eq!("foo\nbar", "foo\nbaz");
@@ -161,6 +176,32 @@ mod assert_eq {
     fn fails_custom_trailing_comma() {
         ::pretty_assertions::assert_eq!(666, 999, "custom panic message",);
     }
+
+    #[test]
+    #[should_panic(expected = r#"assertion failed: `(left == right)`
+
+Diff < left / right > :
+ foo
+<bar
+>baz
+
+"#)]
+    fn fails_str() {
+        ::pretty_assertions::assert_eq!("foo\nbar", "foo\nbaz");
+    }
+
+    #[test]
+    #[should_panic(expected = r#"assertion failed: `(left == right)`
+
+Diff < left / right > :
+ foo
+<bar
+>baz
+
+"#)]
+    fn fails_string() {
+        ::pretty_assertions::assert_eq!("foo\nbar".to_string(), "foo\nbaz".to_string());
+    }
 }
 
 mod assert_ne {