diff --git a/src/third_party/llvm-project/clang/test/Modules/explicit-build.cpp b/src/third_party/llvm-project/clang/test/Modules/explicit-build.cpp
new file mode 100644
index 0000000..16eb604
--- /dev/null
+++ b/src/third_party/llvm-project/clang/test/Modules/explicit-build.cpp
@@ -0,0 +1,204 @@
+// RUN: rm -rf %t
+
+// -------------------------------
+// Build chained modules A, B, and C
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-name=a -emit-module %S/Inputs/explicit-build/module.modulemap -o %t/a.pcm \
+// RUN:            2>&1 | FileCheck --check-prefix=CHECK-NO-IMPLICIT-BUILD %s --allow-empty
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -fmodule-name=b -emit-module %S/Inputs/explicit-build/module.modulemap -o %t/b.pcm \
+// RUN:            2>&1 | FileCheck --check-prefix=CHECK-NO-IMPLICIT-BUILD %s --allow-empty
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/b.pcm \
+// RUN:            -fmodule-name=c -emit-module %S/Inputs/explicit-build/module.modulemap -o %t/c.pcm \
+// RUN:            2>&1 | FileCheck --check-prefix=CHECK-NO-IMPLICIT-BUILD %s --allow-empty
+//
+// CHECK-NO-IMPLICIT-BUILD-NOT: building module
+
+// -------------------------------
+// Build B with an implicit build of A
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-name=b -emit-module %S/Inputs/explicit-build/module.modulemap -o %t/b-not-a.pcm \
+// RUN:            2>&1 | FileCheck --check-prefix=CHECK-B-NO-A %s
+//
+// CHECK-B-NO-A: While building module 'b':
+// CHECK-B-NO-A: building module 'a' as
+
+// -------------------------------
+// Check that we can use the explicitly-built A, B, and C modules.
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -verify %s -DHAVE_A
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-map-file=%S/Inputs/explicit-build/module.modulemap \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -verify %s -DHAVE_A
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/b.pcm \
+// RUN:            -verify %s -DHAVE_A -DHAVE_B
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -fmodule-file=%t/b.pcm \
+// RUN:            -verify %s -DHAVE_A -DHAVE_B
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -fmodule-file=%t/b.pcm \
+// RUN:            -fmodule-file=%t/c.pcm \
+// RUN:            -verify %s -DHAVE_A -DHAVE_B -DHAVE_C
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -fmodule-file=%t/c.pcm \
+// RUN:            -verify %s -DHAVE_A -DHAVE_B -DHAVE_C
+
+// -------------------------------
+// Check that -fmodule-file= in a module build makes the file transitively
+// available even if it's not used.
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fno-implicit-modules -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/b.pcm \
+// RUN:            -fmodule-name=d -emit-module %S/Inputs/explicit-build/module.modulemap -o %t/d.pcm \
+// RUN:            2>&1 | FileCheck --check-prefix=CHECK-NO-IMPLICIT-BUILD %s --allow-empty
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fno-implicit-modules -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/d.pcm \
+// RUN:            -verify %s -DHAVE_A -DHAVE_B
+
+#if HAVE_A
+  #include "a.h"
+  static_assert(a == 1, "");
+#else
+  const int use_a = a; // expected-error {{undeclared identifier}}
+#endif
+
+#if HAVE_B
+  #include "b.h"
+  static_assert(b == 2, "");
+#else
+  const int use_b = b; // expected-error {{undeclared identifier}}
+#endif
+
+#if HAVE_C
+  #include "c.h"
+  static_assert(c == 3, "");
+#else
+  const int use_c = c; // expected-error {{undeclared identifier}}
+#endif
+
+#if HAVE_A && HAVE_B && HAVE_C
+// expected-no-diagnostics
+#endif
+
+// -------------------------------
+// Check that we can use a mixture of implicit and explicit modules.
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/b-not-a.pcm \
+// RUN:            -verify %s -DHAVE_A -DHAVE_B
+
+// -------------------------------
+// Try to use two different flavors of the 'a' module.
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -fmodule-file=%t/b-not-a.pcm \
+// RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-MULTIPLE-AS %s
+//
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -fmodule-file=%t/b-not-a.pcm \
+// RUN:            -fmodule-map-file=%S/Inputs/explicit-build/module.modulemap \
+// RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-MULTIPLE-AS %s
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-name=a -emit-module %S/Inputs/explicit-build/module.modulemap -o %t/a-alt.pcm \
+// RUN:            2>&1 | FileCheck --check-prefix=CHECK-NO-IMPLICIT-BUILD %s --allow-empty
+//
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -fmodule-file=%t/a-alt.pcm \
+// RUN:            -fmodule-map-file=%S/Inputs/explicit-build/module.modulemap \
+// RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-MULTIPLE-AS %s
+//
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/a-alt.pcm \
+// RUN:            -fmodule-file=%t/a.pcm \
+// RUN:            -fmodule-map-file=%S/Inputs/explicit-build/module.modulemap \
+// RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-MULTIPLE-AS %s
+//
+// CHECK-MULTIPLE-AS: error: module 'a' is defined in both '{{.*[/\\]}}a{{.*}}.pcm' and '{{.*[/\\]}}a{{.*}}.pcm'
+
+// -------------------------------
+// Try to import a PCH with -fmodule-file=
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-name=a -emit-pch %S/Inputs/explicit-build/a.h -o %t/a.pch -DBUILDING_A_PCH \
+// RUN:            2>&1 | FileCheck --check-prefix=CHECK-NO-IMPLICIT-BUILD %s --allow-empty
+//
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/a.pch \
+// RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-A-AS-PCH %s
+//
+// CHECK-A-AS-PCH: fatal error: AST file '{{.*}}a.pch' was not built as a module
+
+// -------------------------------
+// Try to import a non-AST file with -fmodule-file=
+//
+// RUN: touch %t/not.pcm
+//
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/not.pcm \
+// RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-BAD-FILE %s
+//
+// CHECK-BAD-FILE: fatal error: file '{{.*}}not.pcm' is not a valid precompiled module file
+
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -fmodule-file=%t/nonexistent.pcm \
+// RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-NO-FILE %s
+//
+// CHECK-NO-FILE: fatal error: module file '{{.*}}nonexistent.pcm' not found: module file not found
+
+// RUN: mv %t/a.pcm %t/a-tmp.pcm
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/c.pcm \
+// RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-NO-FILE-INDIRECT %s
+// RUN: mv %t/a-tmp.pcm %t/a.pcm
+//
+// CHECK-NO-FILE-INDIRECT:      error: module file '{{.*}}a.pcm' not found
+// CHECK-NO-FILE-INDIRECT-NEXT: note: imported by module 'b' in '{{.*}}b.pcm'
+// CHECK-NO-FILE-INDIRECT-NEXT: note: imported by module 'c' in '{{.*}}c.pcm'
+// CHECK-NO-FILE-INDIRECT-NOT:  note:
+
+// -------------------------------
+// Check that we don't get upset if B's timestamp is newer than C's.
+// RUN: touch %t/b.pcm
+//
+// RUN: %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/c.pcm \
+// RUN:            -verify %s -DHAVE_A -DHAVE_B -DHAVE_C
+//
+// ... but that we do get upset if our B is different from the B that C expects.
+//
+// RUN: cp %t/b-not-a.pcm %t/b.pcm
+//
+// RUN: not %clang_cc1 -x c++ -std=c++11 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -Rmodule-build -fno-modules-error-recovery \
+// RUN:            -I%S/Inputs/explicit-build \
+// RUN:            -fmodule-file=%t/c.pcm \
+// RUN:            %s -DHAVE_A -DHAVE_B -DHAVE_C 2>&1 | FileCheck --check-prefix=CHECK-MISMATCHED-B %s
+//
+// CHECK-MISMATCHED-B:      fatal error: module file '{{.*}}b.pcm' is out of date and needs to be rebuilt: module file out of date
+// CHECK-MISMATCHED-B-NEXT: note: imported by module 'c'
+// CHECK-MISMATCHED-B-NOT:  note: