Option to represent all C++ operators.

In its default behavior, bindgen does not emit information for any
C++ operatorXYZ function (unless operatorXYZ is a valid identifier,
which it isn't for C++ overloaded operators).

This PR introduces a new command line option to represent all operators.
This is not useful for those who directly consume the output of bindgen,
but is useful for post-processors. Specifically, consumers will need to
implement the callback to rename these items to something more useful.

Part of google/autocxx#124

bindgen-tests/tests/headers/operator_equals.hpp

@@ -0,0 +1,9 @@
+// bindgen-flags: --represent-cxx-operators --generate-inline-functions -- -x c++
+// bindgen-parse-callbacks: operator-rename
+
+class SomeClass {
+public:
+    bool operator=(const SomeClass& another) {
+        return false;
+    }
+};

bindgen-tests/tests/parse_callbacks/mod.rs

@@ -146,6 +146,19 @@ impl ParseCallbacks for WrapAsVariadicFn {
     }
 }
 
+#[derive(Debug)]
+pub(super) struct OperatorRename;
+
+impl ParseCallbacks for OperatorRename {
+    fn generated_name_override(&self, info: ItemInfo) -> Option<String> {
+        if info.name == "operator=" {
+            Some("operatorequals".to_string())
+        } else {
+            None
+        }
+    }
+}
+
 pub fn lookup(cb: &str) -> Box<dyn ParseCallbacks> {
     match cb {
         "enum-variant-rename" => Box::new(EnumVariantRename),
@@ -154,6 +167,7 @@ pub fn lookup(cb: &str) -> Box<dyn ParseCallbacks> {
         }
         "wrap-as-variadic-fn" => Box::new(WrapAsVariadicFn),
         "type-visibility" => Box::new(TypeVisibility),
+        "operator-rename" => Box::new(OperatorRename),
         call_back => {
             if let Some(prefix) =
                 call_back.strip_prefix("remove-function-prefix-")

bindgen/ir/function.rs

@@ -433,7 +433,7 @@ impl FunctionSig {
             spelling.starts_with("operator") &&
                 !clang::is_valid_identifier(spelling)
         };
-        if is_operator(&spelling) {
+        if is_operator(&spelling) && !ctx.options().represent_cxx_operators {
             return Err(ParseError::Continue);
         }
 

bindgen/options/cli.rs

@@ -444,6 +444,9 @@ struct BindgenCommand {
     /// Use distinct char16_t
     #[arg(long)]
     use_distinct_char16_t: bool,
+    /// Output C++ overloaded operators
+    #[arg(long)]
+    represent_cxx_operators: bool,
     /// Enables generation of vtable functions.
     #[arg(long)]
     vtable_generation: bool,
@@ -633,6 +636,7 @@ where
         c_naming,
         explicit_padding,
         use_distinct_char16_t,
+        represent_cxx_operators,
         vtable_generation,
         sort_semantically,
         merge_extern_blocks,
@@ -931,6 +935,7 @@ where
             c_naming,
             explicit_padding,
             use_distinct_char16_t,
+            represent_cxx_operators,
             vtable_generation,
             sort_semantically,
             merge_extern_blocks,

bindgen/options/mod.rs

@@ -177,6 +177,24 @@ options! {
         },
         as_args: "--use-distinct-char16-t",
     },
+    /// Whether we should output C++ overloaded operators. By itself,
+    /// this option is not sufficient to produce valid output, because
+    /// such operators will have names that are not acceptable Rust
+    /// names (for example `operator=`). If you use this option, you'll also
+    /// have to rename the resulting functions - for example by using
+    /// [`ParseCallbacks::generated_name_override`].
+    represent_cxx_operators: bool {
+        methods: {
+            /// If this is true, output existence of C++ overloaded operators.
+            /// At present, only operator= is noted.
+            /// Disabled by default.
+            pub fn represent_cxx_operators(mut self, doit: bool) -> Builder {
+                self.options.represent_cxx_operators = doit;
+                self
+            }
+        },
+        as_args: "--represent-cxx-operators",
+    },
 
     /// Types that have been blocklisted and should not appear anywhere in the generated code.
     blocklisted_types: RegexSet {