Factor out the Fail lambda from all trycatch calls

gen/src/builtin.rs

@@ -26,7 +26,6 @@ pub struct Builtins<'a> {
     pub rust_str_repr: bool,
     pub rust_slice_new: bool,
     pub rust_slice_repr: bool,
-    pub exception: bool,
     pub relocatable: bool,
     pub relocatable_or_array: bool,
     pub friend_impl: bool,
@@ -138,6 +137,10 @@ pub(super) fn write(out: &mut OutFile) {
         builtin.unsafe_bitcopy_t = true;
     }
 
+    if builtin.trycatch {
+        builtin.ptr_len = true;
+    }
+
     out.begin_block(Block::Namespace("rust"));
     out.begin_block(Block::InlineNamespace("cxxbridge1"));
 
@@ -251,6 +254,19 @@ pub(super) fn write(out: &mut OutFile) {
         writeln!(out, "}};");
     }
 
+    if builtin.trycatch {
+        out.next_section();
+        writeln!(out, "class Fail final {{");
+        writeln!(out, "  ::rust::repr::PtrLen &throw$;");
+        writeln!(out, "public:");
+        writeln!(
+            out,
+            "  Fail(::rust::repr::PtrLen &throw$) : throw$(throw$) {{}}"
+        );
+        writeln!(out, "  void operator()(const char *) noexcept;");
+        writeln!(out, "}};");
+    }
+
     out.end_block(Block::Namespace("detail"));
 
     if builtin.manually_drop {
@@ -401,14 +417,4 @@ pub(super) fn write(out: &mut OutFile) {
     }
 
     out.end_block(Block::Namespace("rust"));
-
-    if builtin.exception {
-        include.cstddef = true;
-        out.begin_block(Block::ExternC);
-        writeln!(
-            out,
-            "const char *cxxbridge1$exception(const char *, ::std::size_t) noexcept;",
-        );
-        out.end_block(Block::ExternC);
-    }
 }

gen/src/write.rs

@@ -847,17 +847,9 @@ fn write_cxx_function_shim<'a>(out: &mut OutFile<'a>, efn: &'a ExternFn) {
     }
     writeln!(out, ";");
     if efn.throws {
-        out.include.cstring = true;
-        out.builtin.exception = true;
         writeln!(out, "        throw$.ptr = nullptr;");
         writeln!(out, "      }},");
-        writeln!(out, "      [&](const char *catch$) noexcept {{");
-        writeln!(out, "        throw$.len = ::std::strlen(catch$);");
-        writeln!(
-            out,
-            "        throw$.ptr = const_cast<char *>(::cxxbridge1$exception(catch$, throw$.len));",
-        );
-        writeln!(out, "      }});");
+        writeln!(out, "      ::rust::detail::Fail(throw$));");
         writeln!(out, "  return throw$;");
     }
     writeln!(out, "}}");

src/cxx.cc

@@ -68,6 +68,9 @@ void cxxbridge1$slice$new(void *self, const void *ptr,
                           std::size_t len) noexcept;
 void *cxxbridge1$slice$ptr(const void *self) noexcept;
 std::size_t cxxbridge1$slice$len(const void *self) noexcept;
+
+// try/catch
+const char *cxxbridge1$exception(const char *, std::size_t len) noexcept;
 } // extern "C"
 
 namespace rust {
@@ -506,6 +509,13 @@ union MaybeUninit {
 };
 } // namespace
 
+namespace repr {
+struct PtrLen final {
+  void *ptr;
+  std::size_t len;
+};
+} // namespace repr
+
 namespace detail {
 // On some platforms size_t is the same C++ type as one of the sized integer
 // types; on others it is a distinct type. Only in the latter case do we need to
@@ -519,6 +529,19 @@ using isize_if_unique =
     typename std::conditional<std::is_same<rust::isize, int64_t>::value ||
                                   std::is_same<rust::isize, int32_t>::value,
                               struct isize_ignore, rust::isize>::type;
+
+class Fail final {
+  repr::PtrLen &throw$;
+
+public:
+  Fail(repr::PtrLen &throw$) : throw$(throw$) {}
+  void operator()(const char *) noexcept;
+};
+
+void Fail::operator()(const char *catch$) noexcept {
+  throw$.len = std::strlen(catch$);
+  throw$.ptr = const_cast<char *>(cxxbridge1$exception(catch$, throw$.len));
+}
 } // namespace detail
 
 } // namespace cxxbridge1