Display which tuple elements did not match when explaining a mismatch in the tuple! macro.

Previously, the matcher explanation would only show what the elements were expected to be. No information was given on which tuple elements did not match and why.

This implements Matcher::explain_match to enhance the output to show which tuple elements did not match and give explanations for each one.

PiperOrigin-RevId: 503913594

Author: hovinenb

googletest/src/matchers/tuple_matcher.rs

@@ -259,8 +259,8 @@ macro_rules! tuple {
 pub mod internal {
     #[cfg(not(google3))]
     use crate as googletest;
-    use googletest::matcher::{Describe, Matcher, MatcherResult};
-    use std::fmt::Debug;
+    use googletest::matcher::{Describe, MatchExplanation, Matcher, MatcherResult};
+    use std::fmt::{Debug, Write};
 
     /// Replaces the first expression with the second at compile time.
     ///
@@ -297,6 +297,22 @@ pub mod internal {
                     })*
                     MatcherResult::Matches
                 }
+
+                fn explain_match(&self, actual: &($($field_type,)*)) -> MatchExplanation {
+                    let mut explanation = format!("which {}", self.describe(self.matches(actual)));
+                    $(match self.$field_number.matches(&actual.$field_number) {
+                        MatcherResult::Matches => {},
+                        MatcherResult::DoesNotMatch => {
+                            writeln!(
+                                &mut explanation,
+                                concat!("Element #", $field_number, " is {:?}, {}"),
+                                actual.$field_number,
+                                self.$field_number.explain_match(&actual.$field_number)
+                            ).unwrap();
+                        }
+                    })*
+                    MatchExplanation::create(explanation)
+                }
             }
 
             impl<$($matcher_type: Describe),*> Describe for $name<$($matcher_type),*> {
@@ -443,10 +459,10 @@ mod tests {
     use googletest::matchers;
     use googletest::{
         google_test,
-        matcher::{Describe, MatcherResult},
+        matcher::{Describe, Matcher, MatcherResult},
         verify_that, Result,
     };
-    use matchers::{eq, not};
+    use matchers::{displays_as, eq, not};
 
     #[google_test]
     fn empty_matcher_matches_empty_tuple() -> Result<()> {
@@ -687,4 +703,31 @@ is a tuple whose values do not respectively match:
 ")
         )
     }
+
+    #[google_test]
+    fn describe_match_shows_which_tuple_element_did_not_match() -> Result<()> {
+        verify_that!(
+            tuple!(eq(1), eq(2)).explain_match(&(1, 3)),
+            displays_as(eq("\
+which is a tuple whose values do not respectively match:
+  is equal to 1,
+  is equal to 2,
+Element #1 is 3, which isn't equal to 2
+"))
+        )
+    }
+
+    #[google_test]
+    fn describe_match_shows_which_two_tuple_elements_did_not_match() -> Result<()> {
+        verify_that!(
+            tuple!(eq(1), eq(2)).explain_match(&(2, 3)),
+            displays_as(eq("\
+which is a tuple whose values do not respectively match:
+  is equal to 1,
+  is equal to 2,
+Element #0 is 2, which isn't equal to 1
+Element #1 is 3, which isn't equal to 2
+"))
+        )
+    }
 }