Chrome Version: 71.0.3569.0
OS: all

Encountered this compilation error recently:

In file included from gen/chrome/browser/extensions/api/generated_api_registration.cc:50:
In file included from ../../chrome/browser/extensions/api/identity/identity_api.h:24:
In file included from ../../chrome/browser/extensions/api/identity/identity_get_accounts_function.h:10:
gen/services/identity/public/mojom/identity_manager.mojom.h:28:10: fatal error: 'services/identity/public/mojom/identity_manager.mojom-shared.h' file not found
#include "services/identity/public/mojom/identity_manager.mojom-shared.h"
         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.


There is a dependency from //chrome/browser/extensions target (which lists identity_api.h in its sources) to //services/identity/public/mojom but apparently //chrome/browser/extensions/api:api_registration also uses identity_api.h implicitly and is missing the dependency to generate the mojo include.


This seems like a more general error:

targetA builds header.h which includes mojom.h, but it's fine as long as targetA also depends on targetM which generates mojom.h. targetA's dependencies will be built before header.h. 
But if targetA depends on targetB, which also happens to build header.h, it's a problem. targetB may be build before other targetA's deps, potentially before targetM.

There are dozens of api headers referenced in generated_api_resources.cc and potentially lots of issues like this.