Fix handling of anonymous names in Clang 16.

In trunk, Clang started emitting names like `"(unnamed enum at foo.cpp:4:2)"`
for unnamed enums, structs, and unions, while previous versions emitted the
empty string. This caused panics.

This commit simply rewrites such names back to the empty string so that we stay
compatible with both old and new versions of Clang.

Closes rust-lang#2312.

Author: pcwalton

bindgen/ir/comp.rs

@@ -12,6 +12,7 @@ use super::ty::RUST_DERIVE_IN_ARRAY_LIMIT;
 use crate::clang;
 use crate::codegen::struct_layout::{align_to, bytes_from_bits_pow2};
 use crate::ir::derive::CanDeriveCopy;
+use crate::ir::item;
 use crate::parse::{ClangItemParser, ParseError};
 use crate::HashMap;
 use crate::NonCopyUnionStyle;
@@ -1422,7 +1423,9 @@ impl CompInfo {
 
                         // A declaration of an union or a struct without name
                         // could also be an unnamed field, unfortunately.
-                        if cur.spelling().is_empty() &&
+                        let mut spelling = cur.spelling();
+                        item::normalize_name_for_clang_16(&mut spelling);
+                        if spelling.is_empty() &&
                             cur.kind() != CXCursor_EnumDecl
                         {
                             let ty = cur.cur_type();

bindgen/ir/item.rs

@@ -2016,3 +2016,16 @@ impl<'a> NameOptions<'a> {
         self.item.real_canonical_name(self.ctx, self)
     }
 }
+
+/// Normalizes names so that we can handle them identically in Clang 16 and earlier versions.
+///
+/// In Clang 16, anonymous names have names like `(anonymous union at foo.c:16)`, whereas in earlier
+/// versions of Clang they were the empty string. This function normalizes all such names to the
+/// empty string so that we can handle them identically.
+pub fn normalize_name_for_clang_16(name: &mut String) {
+    // This may seem fragile, but ")" is not a valid character in C identifiers, so it should
+    // actually be a reasonably robust check.
+    if name.ends_with(")") {
+        name.truncate(0);
+    }
+}

bindgen/ir/ty.rs

@@ -14,6 +14,7 @@ use super::template::{
 };
 use super::traversal::{EdgeKind, Trace, Tracer};
 use crate::clang::{self, Cursor};
+use crate::ir::item;
 use crate::parse::{ClangItemParser, ParseError, ParseResult};
 use std::borrow::Cow;
 use std::io;
@@ -1112,6 +1113,8 @@ impl Type {
                         }
                     }
 
+                    item::normalize_name_for_clang_16(&mut name);
+
                     TypeKind::Enum(enum_)
                 }
                 CXType_Record => {
@@ -1132,6 +1135,8 @@ impl Type {
                         }
                     }
 
+                    item::normalize_name_for_clang_16(&mut name);
+
                     TypeKind::Comp(complex)
                 }
                 CXType_Vector => {