Add `disable_nested_struct_naming` option (#1610)

The following structs have different names for C and C++. In case of C
they are visible as `foo` and `bar`. In case of C++ they are visible as
`foo` and `foo::bar`. By default bindgen follows C++ naming to avoid
generating duplicate names.

With this option the following structs will be named as `foo`
and `bar` instead of `foo` and `foo_bar`.

```
struct foo {
    struct bar {
    } b;
};
```

In case of an unnamed definition we build the canonical name from
the inner most named definition. For example the following will
generate `baz__bindgen_ty_1`:

```
struct foo {
    struct bar {
        struct baz {
            struct {
            } u;
        } z;
    } b;
};
```

This option should be used only for C headers. It is needed in some
rare situations where user used another code generator that already
mangled nested definitions.

A real life example is [asn1c] with `-fcompound-names` option.

[asn1c]: https://github.com/vlm/asn1c

1 files changed, 24 insertions, 0 deletions

diff --git a/tests/headers/disable-nested-struct-naming.h b/tests/headers/disable-nested-struct-naming.h
new file mode 100644
index 00000000..0e4fccb6
--- /dev/null
+++ b/tests/headers/disable-nested-struct-naming.h
@@ -0,0 +1,24 @@
+// bindgen-flags: --disable-nested-struct-naming
+
+struct foo {
+    struct bar1 {
+        int x1;
+        struct {
+            int x2;
+            struct {
+                int x3;
+                struct bar4 {
+                    int x4;
+                } b4;
+            } b3;
+        } b2;
+    } b1;
+};
+
+struct {
+    struct {
+        struct baz {
+            int x;
+        } b;
+    } anon2;
+} anon1;