debugging zig c backend duplicate typedef; https://github.com/ziglang/zig/issues/11651

debug output

new f4a0c58216b9dad9       const_slice_u8 "typedef struct { uint8_t const * ptr; size_t len; } zig_L_u8;\n"
new fd5814f465beb2c5                tuple "typedef struct {\n uintptr_t field_0;\n uint8_t field_1;\n} zig_T_tuple_7busize_2c_20u1_7d;\n"
new 8d02975f3a25a947  array_u8_sentinel_0 "typedef uint8_t zig_A_u8_5[5];\n"
new d5d7770a0890948e             array_u8 "typedef uint8_t zig_A_u8_1[1];\n"
    f4a0c58216b9dad9       const_slice_u8 "typedef struct { uint8_t const * ptr; size_t len; } zig_L_u8;\n"
new 4487d943b4f83aed  array_u8_sentinel_0 "typedef uint8_t zig_A_u8_1[1];\n"
    f4a0c58216b9dad9       const_slice_u8 "typedef struct { uint8_t const * ptr; size_t len; } zig_L_u8;\n"
    f4a0c58216b9dad9       const_slice_u8 "typedef struct { uint8_t const * ptr; size_t len; } zig_L_u8;\n"
new 25da5e8e385153e6 single_const_pointer "typedef uint16_t (*zig_F__2aconst_20fn_28_29_20anyerror_21void)(void);\n"
new  3b32fc1c5510a94             optional "typedef struct { uintptr_t payload; bool is_null; } zig_Q_usize;\n"
new d3026fb9de972f53               struct "typedef struct {\n zig_L_u8 name;\n zig_F__2aconst_20fn_28_29_20anyerror_21void func;\n zig_Q_usize async_frame_size;\n} zig_S_builtin_TestFn;\n"
    f4a0c58216b9dad9       const_slice_u8 "typedef struct { uint8_t const * ptr; size_t len; } zig_L_u8;\n"
    25da5e8e385153e6 single_const_pointer "typedef uint16_t (*zig_F__2aconst_20fn_28_29_20anyerror_21void)(void);\n"
     3b32fc1c5510a94             optional "typedef struct { uintptr_t payload; bool is_null; } zig_Q_usize;\n"
    d3026fb9de972f53               struct "typedef struct {\n zig_L_u8 name;\n zig_F__2aconst_20fn_28_29_20anyerror_21void func;\n zig_Q_usize async_frame_size;\n} zig_S_builtin_TestFn;\n"
new 6dc2604353536964          const_slice "typedef struct { zig_S_builtin_TestFn const * ptr; size_t len; } zig_L_builtin_TestFn;\n"
    f4a0c58216b9dad9       const_slice_u8 "typedef struct { uint8_t const * ptr; size_t len; } zig_L_u8;\n"
new cabb949c9d4755d6            mut_slice "typedef struct { uintptr_t * ptr; size_t len; } zig_M_usize;\n"
new 7d147ecdb904467f               struct "typedef struct {\n uintptr_t index;\n zig_M_usize instruction_addresses;\n} zig_S_builtin_StackTrace;\n"
    f4a0c58216b9dad9       const_slice_u8 "typedef struct { uint8_t const * ptr; size_t len; } zig_L_u8;\n"
    25da5e8e385153e6 single_const_pointer "typedef uint16_t (*zig_F__2aconst_20fn_28_29_20anyerror_21void)(void);\n"
     3b32fc1c5510a94             optional "typedef struct { uintptr_t payload; bool is_null; } zig_Q_usize;\n"
    d3026fb9de972f53               struct "typedef struct {\n zig_L_u8 name;\n zig_F__2aconst_20fn_28_29_20anyerror_21void func;\n zig_Q_usize async_frame_size;\n} zig_S_builtin_TestFn;\n"
new 4aa7cc831f5a8ee5            mut_slice "typedef struct { zig_S_builtin_TestFn * ptr; size_t len; } zig_M_builtin_TestFn;\n"
    fd5814f465beb2c5                tuple "typedef struct {\n uintptr_t field_0;\n uint8_t field_1;\n} zig_T_tuple_7busize_2c_20u1_7d;\n"
    f4a0c58216b9dad9       const_slice_u8 "typedef struct { uint8_t const * ptr; size_t len; } zig_L_u8;\n"

print-debug-table.patch

diff --git a/src/link/C.zig b/src/link/C.zig
index 4159a577d..b0349fc1b 100644
--- a/src/link/C.zig
+++ b/src/link/C.zig
@@ -384,8 +384,12 @@ fn flushDecl(self: *C, f: *Flush, decl_index: Module.Decl.Index) FlushDeclError!
                 .mod = module,
             });
             if (!gop.found_existing) {
+                std.debug.print("new ", .{});
                 try f.err_typedef_buf.appendSlice(gpa, new.value_ptr.rendered);
+            } else {
+                std.debug.print("    ", .{});
             }
+            std.debug.print("{x: >16} {s: >20} \"{}\"\n", .{ (Type.HashContext64{ .mod = module }).hash(new.key_ptr.*), @tagName(new.key_ptr.*.tag()), std.zig.fmtEscapes(new.value_ptr.rendered) });
         }
     }