[Clang] Improve error message for violations of -fmodules-decluse.

[jyknight]

Summary

Now it reports the name of the indirectly-used module which is
missing.

[ChuanqiXu]

LGTM. Thanks.

clang/include/clang/Basic/DiagnosticLexKinds.td

def warn_mmap_umbrella_dir_not_found : Warning<
   InGroup<IncompleteUmbrella>;
 def err_expected_id_building_module : Error<
   "expected a module name in '__building_module' expression">;
 def warn_use_of_private_header_outside_module : Warning<
   "use of private header from outside its module: '%0'">,
   InGroup<DiagGroup<"private-header">>, DefaultError;
 def err_undeclared_use_of_module : Error<
   "module %0 does not depend on a module exporting '%1'">;
+def err_undeclared_use_of_module_indirect : Error<
+  "module %0 does not directly depend on a module exporting '%1', which is part of indirectly-used module %2">;
 def warn_non_modular_include_in_framework_module : Warning<
   "include of non-modular header inside framework module '%0': '%1'">,
   InGroup<NonModularIncludeInFrameworkModule>, DefaultIgnore;
 def warn_non_modular_include_in_module : Warning<
   "include of non-modular header inside module '%0': '%1'">,
   InGroup<NonModularIncludeInModule>, DefaultIgnore;
 def warn_module_conflict : Warning<
   "module '%0' conflicts with already-imported module '%1': %2">,

clang/lib/Lex/ModuleMap.cpp

void ModuleMap::diagnoseHeaderInclusion(Module *RequestingModule,
   if (Private) {
     Diags.Report(FilenameLoc, diag::warn_use_of_private_header_outside_module)
         << Filename;
     return;
   }
 
   // We have found a module, but we don't use it.
   if (NotUsed) {
-    Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module)
-        << RequestingModule->getTopLevelModule()->Name << Filename;
+    Diags.Report(FilenameLoc, diag::err_undeclared_use_of_module_indirect)
+        << RequestingModule->getTopLevelModule()->Name << Filename
+        << NotUsed->Name;
     return;
   }
 
   if (Excluded || isHeaderInUmbrellaDirs(File))
     return;
 
   // At this point, only non-modular includes remain.
 

clang/test/Modules/Inputs/declare-use/h.h

 #ifndef H_H
 #define H_H
 #include "c.h"
-#include "d.h" // expected-error {{module XH does not depend on a module exporting}}
+#include "d.h" // expected-error {{module XH does not directly depend on a module exporting 'd.h', which is part of indirectly-used module XD}}
 #include "h1.h"
 const int h1 = aux_h*c*7*d;
 #endif

clang/test/Modules/declare-use-textual.cpp

 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-decluse -fmodule-name=Textual -I %S/Inputs/declare-use %s -verify
 // RUN: %clang_cc1 -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-decluse -fmodule-name=Textual -I %S/Inputs/declare-use %s -fno-modules-validate-textual-header-includes
 
-// expected-error@textual.h:* {{module Textual does not depend on a module exporting 'a.h'}}
+// expected-error@textual.h:* {{module Textual does not directly depend on a module exporting 'a.h', which is part of indirectly-used module XA}}
 #include "textual.h"

clang/test/Modules/declare-use1.cpp

 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fimplicit-module-maps -fmodules-decluse -fmodule-name=XG -I %S/Inputs/declare-use %s -verify
 //
 // Check these flags get properly passed through the driver even when -fmodules is disabled.
 // RUN: %clang -fimplicit-module-maps -fmodules-decluse -fmodule-name=XG -I %S/Inputs/declare-use -fsyntax-only -Xclang -verify %s
 
 #include "g.h"
 #include "e.h"
-#include "f.h" // expected-error {{module XG does not depend on a module exporting 'f.h'}}
+#include "f.h" // expected-error {{module XG does not directly depend on a module exporting 'f.h', which is part of indirectly-used module XF}}
 #include "i.h"
 #include "sub.h"
 const int g2 = g1 + e + f + aux_i + sub;

clang/test/Modules/declare-use2.cpp

 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-decluse -fmodule-name=XH -I %S/Inputs/declare-use %s -verify
 
 #include "h.h"
 #include "e.h"
-#include "f.h" // expected-error {{module XH does not depend on a module exporting 'f.h'}}
+#include "f.h" // expected-error {{module XH does not directly depend on a module exporting 'f.h', which is part of indirectly-used module XF}}
 const int h2 = h1+e+f;

clang/test/Modules/declare-use3.cpp

 // RUN: rm -rf %t
 // RUN: %clang_cc1 -include "g.h" -include "e.h" -include "f.h" -include "i.h" -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-decluse -fmodule-name=XG -I %S/Inputs/declare-use %s -verify
-// expected-error {{module XG does not depend on a module exporting 'f.h'}}
+// expected-error {{module XG does not directly depend on a module exporting 'f.h', which is part of indirectly-used module XF}}
 const int g2 = g1 + e + f + aux_i;

clang/test/Modules/strict-decluse.cpp

 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-strict-decluse -fmodule-name=XG -I %S/Inputs/declare-use %s -verify
 
 #include "g.h"
 #include "e.h"
-#include "f.h" // expected-error {{module XG does not depend on a module exporting 'f.h'}}
+#include "f.h" // expected-error {{module XG does not directly depend on a module exporting 'f.h', which is part of indirectly-used module XF}}
 #include "i.h" // expected-error {{module XG does not depend on a module exporting 'i.h'}}
 
 const int g2 = g1 + e + f + aux_i;

clang/test/Modules/string_names.cpp

 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -fmodules-decluse -I %S/Inputs/string_names %s -fmodule-name="my/module-a" -verify
 
 // Check that we can preprocess with string module names.
 // RUN: %clang_cc1 -fmodules-cache-path=%t -fmodules -fimplicit-module-maps -I %S/Inputs/string_names %s -fmodule-name="my/module-a" -E -frewrite-imports -o %t/test.ii
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-decluse -I %S/Inputs/string_names %t/test.ii -fmodule-name="my/module-a"
 
 #include "a.h"
-#include "b.h" // expected-error {{does not depend on a module exporting}}
+#include "b.h" // expected-error {{module my/module-a does not directly depend on a module exporting 'b.h', which is part of indirectly-used module my/module-b}}
 #include "c.h"

clang/test/Modules/textual-headers.cpp

 // RUN: rm -rf %t
 // RUN: %clang_cc1 -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-strict-decluse -fmodule-name=XG -I %S/Inputs/declare-use %s -verify
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -fmodules-strict-decluse -fmodule-name=XG -I %S/Inputs/declare-use %s -verify -fno-modules-error-recovery
 
 #define GIMME_A_K
 #include "k.h"
 
 #define GIMME_AN_L
-#include "l.h" // expected-error {{module XG does not depend on a module exporting 'l.h'}}
+#include "l.h" // expected-error {{module XG does not directly depend on a module exporting 'l.h', which is part of indirectly-used module XL}}
 
-#include "m2.h" // expected-error {{module XG does not depend on a module exporting 'm2.h'}}
+#include "m2.h" // expected-error {{module XG does not directly depend on a module exporting 'm2.h', which is part of indirectly-used module XM}}
 const int use_m = m; // expected-error {{undeclared identifier}}
 
 #define GIMME_AN_M
 #include "m.h" // expected-error {{use of private header from outside its module: 'm.h'}}
 const int use_m_2 = m;
 
 const int g = k + l;