Fix the parsing logic of matches_pattern! to support _ at the top level in top-level structs.

In the current parsing logic, the `_` field in pattern `Some(_)` is parsed as `None`, and as a result no FieldMatcher is generated, and the internal `is()` matcher only evaluates the innerMatcher(the field_matcher).

We add `pattern_only()` matcher for the case when field_matcher is empty and skip the `is()` wrapping.

Toward #626

PiperOrigin-RevId: 748656817

Author: Googler

googletest/src/matchers/matches_pattern.rs

@@ -246,7 +246,8 @@
 /// #    .unwrap();
 /// ```
 ///
-/// One can also match enum values:
+/// The macro also allows matching on specific enum values and supports wildcard
+/// patterns like `MyEnum::Case(_)`.
 ///
 /// ```
 /// # use googletest::prelude::*;
@@ -260,11 +261,16 @@
 /// verify_that!(MyEnum::A(123), matches_pattern!(&MyEnum::A(eq(123))))?; // Passes
 /// #     Ok(())
 /// # }
+/// # fn should_pass_with_wildcard() -> Result<()> {
+/// verify_that!(MyEnum::A(123), matches_pattern!(MyEnum::A(_)))?; // Passes
+/// #     Ok(())
+/// # }
 /// # fn should_fail() -> Result<()> {
 /// verify_that!(MyEnum::B, matches_pattern!(&MyEnum::A(eq(123))))?; // Fails - wrong enum variant
 /// #     Ok(())
 /// # }
 /// # should_pass().unwrap();
+/// # should_pass_with_wildcard().unwrap();
 /// # should_fail().unwrap_err();
 /// ```
 ///

googletest/tests/matches_pattern_test.rs

@@ -639,6 +639,112 @@ fn generates_correct_failure_output_when_enum_variant_without_field_is_matched()
     const EXPECTED: &str = "is & AnEnum :: A";
     verify_that!(result, err(displays_as(contains_substring(EXPECTED))))
 }
+
+#[test]
+fn has_failure_when_wrong_enum_variant_is_matched_non_exhaustively() -> Result<()> {
+    #[allow(dead_code)]
+    #[derive(Debug)]
+    enum AnEnum {
+        Variant1(i8),
+        Variant2,
+    }
+    let actual: AnEnum = AnEnum::Variant2;
+
+    let result = verify_that!(actual, matches_pattern!(&AnEnum::Variant1(..)));
+
+    const EXPECTED: &str = indoc!(
+        "
+        Expected: is & AnEnum :: Variant1(..)
+        Actual: Variant2,
+          which is not & AnEnum :: Variant1(..)
+        "
+    );
+    verify_that!(result, err(displays_as(contains_substring(EXPECTED))))
+}
+
+#[test]
+fn has_failure_when_wrong_enum_variant_is_matched_with_underscore() -> Result<()> {
+    #[allow(dead_code)]
+    #[derive(Debug)]
+    enum AnEnum {
+        Variant1(i8),
+        Variant2,
+    }
+    let actual: AnEnum = AnEnum::Variant2;
+
+    let result = verify_that!(actual, matches_pattern!(&AnEnum::Variant1(_)));
+
+    const EXPECTED: &str = indoc!(
+        "
+        Expected: is & AnEnum :: Variant1(_)
+        Actual: Variant2,
+          which is not & AnEnum :: Variant1(_)
+        "
+    );
+    verify_that!(result, err(displays_as(contains_substring(EXPECTED))))
+}
+
+#[test]
+fn has_failure_when_wrong_enum_variant_is_matched_with_value() -> Result<()> {
+    #[allow(dead_code)]
+    #[derive(Debug)]
+    enum AnEnum {
+        Variant1(i8),
+        Variant2,
+    }
+    let actual: AnEnum = AnEnum::Variant2;
+
+    let result = verify_that!(actual, matches_pattern!(&AnEnum::Variant1(123)));
+
+    const EXPECTED: &str = indoc!(
+        "
+        Expected: is & AnEnum :: Variant1 which has field `0`, which is equal to 123
+        Actual: Variant2,
+          which has the wrong enum variant `Variant2`
+        "
+    );
+    verify_that!(result, err(displays_as(contains_substring(EXPECTED))))
+}
+
+#[test]
+fn matches_enum_struct_field_with_mutliple_variants() -> Result<()> {
+    #[allow(dead_code)]
+    #[derive(Debug)]
+    enum AnEnum {
+        Variant1(i8),
+        Variant2,
+    }
+    let actual: AnEnum = AnEnum::Variant2;
+
+    verify_that!(actual, matches_pattern!(&AnEnum::Variant2))
+}
+
+#[test]
+fn matches_enum_struct_field_with_multiple_variants_non_exhaustive() -> Result<()> {
+    #[allow(dead_code)]
+    #[derive(Debug)]
+    enum AnEnum {
+        Variant1(i8),
+        Variant2,
+    }
+    let actual: AnEnum = AnEnum::Variant1(123);
+
+    verify_that!(actual, matches_pattern!(&AnEnum::Variant1(..)))
+}
+
+#[test]
+fn matches_enum_struct_field_with_multiple_variants_with_wildcard() -> Result<()> {
+    #[allow(dead_code)]
+    #[derive(Debug)]
+    enum AnEnum {
+        Variant1(i8),
+        Variant2,
+    }
+    let actual: AnEnum = AnEnum::Variant1(123);
+
+    verify_that!(actual, matches_pattern!(&AnEnum::Variant1(_)))
+}
+
 #[test]
 fn matches_enum_with_field() -> Result<()> {
     #[derive(Debug)]

googletest_macro/src/matches_pattern.rs

@@ -167,43 +167,70 @@ fn parse_tuple_pattern_args(
     let (patterns, dot_dot) =
         parse_list_terminated_pattern::<MaybeTupleFieldPattern>.parse2(group_content)?;
     let field_count = patterns.len();
-    let field_patterns = patterns
+    let field_patterns: Vec<_> = patterns
         .into_iter()
         .enumerate()
         .filter_map(|(index, maybe_pattern)| maybe_pattern.0.map(|pattern| (index, pattern)))
         .map(|(index, TupleFieldPattern { ref_token, matcher })| {
             let index = syn::Index::from(index);
             quote! { googletest::matchers::field!(#struct_name.#index, #ref_token #matcher) }
-        });
+        })
+        .collect();
 
-    let matcher = quote! {
-        googletest::matchers::__internal_unstable_do_not_depend_on_these::is(
-            stringify!(#struct_name),
-            all!( #(#field_patterns),* )
-        )
-    };
+    if field_patterns.is_empty() {
+        // It is possible that the logic above didn't generate any field matchers
+        // (e.g., for patterns like `Some(_)`).
+        // In this case we verify that the enum has the correct case, but don't
+        // verify the payload.
+        #[allow(clippy::manual_repeat_n)]
+        // `repeat_n` is not available on the Rust MSRV that we support in OSS
+        let ignored_fields = std::iter::repeat(quote! { _ })
+            .take(field_count)
+            .chain(dot_dot.map(ToTokens::into_token_stream));
+        let full_pattern = quote! { #struct_name ( #(#ignored_fields),* ) };
 
-    // Do a match to ensure:
-    // - Fields are exhaustively listed unless the pattern ended with `..`.
-    // - `UNDEFINED_SYMBOL(..)` fails to compile.
-    let empty_fields = std::iter::repeat(quote! { _ })
-        .take(field_count)
-        .chain(dot_dot.map(ToTokens::into_token_stream));
-    Ok(quote! {
-        googletest::matchers::__internal_unstable_do_not_depend_on_these::compile_assert_and_match(
-            |actual| {
-                // Exhaustively check that all field names are specified.
-                match actual {
-                    #struct_name ( #(#empty_fields),* ) => (),
-                    // The pattern below is unreachable if the type is a struct (as opposed to
-                    // an enum). Since the macro can't know which it is, we always include it
-                    // and just tell the compiler not to complain.
-                    #[allow(unreachable_patterns)]
-                    _ => {},
-                }
-            },
-            #matcher)
-    })
+        Ok(quote! {
+            googletest::matchers::__internal_unstable_do_not_depend_on_these::pattern_only(
+                |actual| { matches!(actual, #full_pattern) },
+                concat!("is ", stringify!(#full_pattern)),
+                concat!("is not ", stringify!(#full_pattern))
+            )
+        })
+    } else {
+        // We have created at least one field matcher. Each field matcher will verify
+        // not only its part of the payload, but also that the enum has the
+        // correct case.
+        let matcher = quote! {
+            googletest::matchers::__internal_unstable_do_not_depend_on_these::is(
+                stringify!(#struct_name),
+                all!( #(#field_patterns),* )
+            )
+        };
+
+        // Do a match to ensure:
+        // - Fields are exhaustively listed unless the pattern ended with `..`.
+        // - `UNDEFINED_SYMBOL(..)` fails to compile.
+        #[allow(clippy::manual_repeat_n)]
+        // `repeat_n` is not available on the Rust MSRV that we support in OSS
+        let empty_fields = std::iter::repeat(quote! { _ })
+            .take(field_count)
+            .chain(dot_dot.map(ToTokens::into_token_stream));
+        Ok(quote! {
+            googletest::matchers::__internal_unstable_do_not_depend_on_these::compile_assert_and_match(
+                |actual| {
+                    // Exhaustively check that all field names are specified.
+                    match actual {
+                        #struct_name ( #(#empty_fields),* ) => (),
+                        // The pattern below is unreachable if the type is a struct (as opposed to
+                        // an enum). Since the macro can't know which it is, we always include it
+                        // and just tell the compiler not to complain.
+                        #[allow(unreachable_patterns)]
+                        _ => {},
+                    }
+                },
+                #matcher)
+        })
+    }
 }
 
 ////////////////////////////////////////////////////////////////////////////////