% tree                                                                                              :(
.
└── D
    └── E
        ├── F.d
        └── I.d

2 directories, 2 files
% cat D/E/F.d
module H;
import D.E.I;

struct K
{
    L* M;
}

struct N
{
    K O;
    P Q;
}

% cat D/E/I.d
module D.E.I;
alias P = long;

% dmd D/E/I.d D/E/F.d 
D/E/F.d(6): Error: undefined identifier 'L'
core.exception.AssertError@declaration.d(2061): Assertion failure
----------------
4   dmd                                 0x00000001097b7854 _d_assert + 104
5   dmd                                 0x000000010958c86a void ddmd.declaration.__assert(int) + 38
6   dmd                                 0x00000001095c36e1 _ZN14VarDeclaration16isOverlappedWithEPS_ + 81
7   dmd                                 0x0000000109590c0c _ZN20AggregateDeclaration21checkOverlappedFieldsEv + 316
8   dmd                                 0x00000001095ec1ca _ZN17StructDeclaration12finalizeSizeEv + 330
9   dmd                                 0x0000000109590a0d _ZN20AggregateDeclaration13determineSizeE3Loc + 221
10  dmd                                 0x00000001095903e9 _ZN20AggregateDeclaration9semantic2EP5Scope + 89
11  dmd                                 0x00000001095e1ab1 _ZN6Module9semantic2EP5Scope + 113
12  dmd                                 0x0000000109665d2c int ddmd.mars.tryMain(ulong, const(char)**) + 13348
13  dmd                                 0x000000010958d8d2 _Dmain + 38
14  dmd                                 0x00000001097c838b D2rt6dmain211_d_run_mainUiPPaPUAAaZiZ6runAllMFZ9__lambda1MFZv + 39
15  dmd                                 0x00000001097c82bf void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).tryExec(scope void delegate()) + 35
16  dmd                                 0x00000001097c8330 void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).runAll() + 44
17  dmd                                 0x00000001097c82bf void rt.dmain2._d_run_main(int, char**, extern (C) int function(char[][])*).tryExec(scope void delegate()) + 35
18  dmd                                 0x00000001097c8225 _d_run_main + 497
19  dmd                                 0x000000010958d96b main + 15
20  dmd                                 0x000000010958bf13 start + 51
21  ???                                 0x0000000000000002 0x0 + 2