Make matches_pattern support _ at the top level in braced structs.

This change is not backward-compatible since:
* Some things that previously fell back to `match` pattern matching now use `match_pattern!`'s specialized matching, which requires the matched object to implement `Debug`.

Toward #447

PiperOrigin-RevId: 703619892

Author: marcianx

googletest/src/matchers/matches_pattern.rs

@@ -372,6 +372,18 @@ pub mod internal {
 }
 
 mod compile_fail_tests {
+    /// ```compile_fail
+    /// use ::googletest::prelude::*;
+    /// #[derive(Debug)]
+    /// struct Foo { a: u32 }
+    /// impl Foo {
+    ///   fn b() {}
+    /// }
+    /// let actual = Foo { a: 1 };
+    /// verify_that!(actual, matches_pattern!(Foo { a: eq(&1), b(): _ }));
+    /// ```
+    fn _underscore_unsupported_for_methods() {}
+
     /// ```compile_fail
     /// use ::googletest::prelude::*;
     /// #[derive(Debug)]

googletest/tests/matches_pattern_test.rs

@@ -150,6 +150,23 @@ fn matches_struct_containing_non_copy_field_binding_mode() -> Result<()> {
     verify_that!(actual, matches_pattern!(AStruct { a_string: eq("123") }))
 }
 
+#[test]
+fn matches_struct_with_interleaved_underscore() -> Result<()> {
+    #[derive(Debug)]
+    struct NonCopy;
+    #[allow(dead_code)]
+    #[derive(Debug)]
+    struct AStruct {
+        a: u32,
+        b: NonCopy,
+        c: u32,
+    }
+    let actual = AStruct { a: 1, b: NonCopy, c: 3 };
+
+    verify_that!(actual, matches_pattern!(&AStruct { a: eq(1), b: _, c: eq(3) }))?;
+    verify_that!(actual, matches_pattern!(AStruct { a: eq(&1), b: _, c: eq(&3) }))
+}
+
 #[test]
 fn has_correct_assertion_failure_message_for_single_field() -> Result<()> {
     #[derive(Debug)]

googletest_macro/src/matches_pattern.rs

@@ -204,21 +204,32 @@ impl Parse for FieldOrMethod {
 }
 
 /// Either field or method call matcher. E.g.:
-/// * `field: starts_with("something")`
+/// * `field: starts_with("something")` or `field: _`
 /// * `property(arg1, arg2): starts_with("something")
 struct FieldOrMethodPattern {
     ref_token: Option<Token![ref]>,
     field_or_method: FieldOrMethod,
-    matcher: Expr,
+    /// When `None`, it represents `_` which matches anything, meaning we should
+    /// ignore it.
+    matcher: Option<Expr>,
 }
 
 impl Parse for FieldOrMethodPattern {
     fn parse(input: ParseStream) -> syn::Result<Self> {
-        Ok(FieldOrMethodPattern {
-            field_or_method: input.parse()?,
-            ref_token: input.parse()?,
-            matcher: input.parse()?,
-        })
+        let field_or_method: FieldOrMethod = input.parse()?;
+        let underscore = input.parse::<Option<Token![_]>>()?;
+        match underscore {
+            Some(underscore) if matches!(field_or_method, FieldOrMethod::Method(_)) => compile_err(
+                underscore.spans[0],
+                "Don't match a method call against `_`. Just omit it instead.",
+            ),
+            Some(_) => Ok(FieldOrMethodPattern { field_or_method, ref_token: None, matcher: None }),
+            None => Ok(FieldOrMethodPattern {
+                field_or_method,
+                ref_token: input.parse()?,
+                matcher: Some(input.parse()?),
+            }),
+        }
     }
 }
 
@@ -231,13 +242,17 @@ fn parse_braced_pattern_args(
     let mut field_names = vec![];
     let field_patterns: Vec<TokenStream> = patterns
         .into_iter()
-        .map(|FieldOrMethodPattern { ref_token, field_or_method, matcher }| match field_or_method {
-            FieldOrMethod::Field(ident) => {
-                field_names.push(ident.clone());
-                quote! { field!(#struct_name . #ident, #ref_token #matcher) }
-            }
-            FieldOrMethod::Method(call) => {
-                quote! { property!(#struct_name . #call, #ref_token #matcher) }
+        .filter_map(|FieldOrMethodPattern { ref_token, field_or_method, matcher }| {
+            match field_or_method {
+                FieldOrMethod::Field(ident) => {
+                    field_names.push(ident.clone());
+                    matcher.map(|matcher| {
+                        quote! { field!(#struct_name . #ident, #ref_token #matcher) }
+                    })
+                }
+                FieldOrMethod::Method(call) => {
+                    Some(quote! { property!(#struct_name . #call, #ref_token #matcher) })
+                }
             }
         })
         .collect();