3 files changed, 13 insertions, 0 deletions
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index fc6773d21c5..b5f20608c14 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -3925,6 +3925,12 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back("-fmodules-strict-decluse");
   }
 
+  // -fno-implicit-modules turns off implicitly compiling modules on demand.
+  if (!Args.hasFlag(options::OPT_fimplicit_modules,
+                    options::OPT_fno_implicit_modules)) {
+    CmdArgs.push_back("-fno-implicit-modules");
+  }
+
   // -fmodule-name specifies the module that is currently being built (or
   // used for header checking by -fmodule-maps).
   Args.AddLastArg(CmdArgs, options::OPT_fmodule_name);
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 5d554b717b3..832aee22063 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -1378,6 +1378,12 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
 
     auto Override = ModuleFileOverrides.find(ModuleName);
     bool Explicit = Override != ModuleFileOverrides.end();
+    if (!Explicit && !getLangOpts().ImplicitModules) {
+      getDiagnostics().Report(ModuleNameLoc, diag::err_module_build_disabled)
+          << ModuleName;
+      ModuleBuildFailed = true;
+      return ModuleLoadResult();
+    }
 
     std::string ModuleFileName =
         Explicit ? Override->second
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 4c1ac0a148a..7a53cedc93b 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1513,6 +1513,7 @@ static void ParseLangArgs(LangOptions &Opts, ArgList &Args, InputKind IK,
   Opts.ModulesErrorRecovery = !Args.hasArg(OPT_fno_modules_error_recovery);
   Opts.ModulesImplicitMaps = Args.hasFlag(OPT_fmodules_implicit_maps,
                                           OPT_fno_modules_implicit_maps, true);
+  Opts.ImplicitModules = !Args.hasArg(OPT_fno_implicit_modules);
   Opts.CharIsSigned = Opts.OpenCL || !Args.hasArg(OPT_fno_signed_char);
   Opts.WChar = Opts.CPlusPlus && !Args.hasArg(OPT_fno_wchar);
   Opts.ShortWChar = Args.hasFlag(OPT_fshort_wchar, OPT_fno_short_wchar, false);