[Driver] SR-3352: Warn on and ignore -embed-bitcode when not generating object files (#7962)

Commands like -emit-sil and -emit-module (on its own) do not produce object files.
When -embed-bitcode is also set, the driver runs a backend job to generate a module that fails.
This commit emits a warning instead and ignores the -embed-bitcode option.

https://bugs.swift.org/browse/SR-3352

Author: matthewcarroll

include/swift/AST/DiagnosticsDriver.def

@@ -125,6 +125,9 @@ ERROR(error_conflicting_options, none,
       "conflicting options '%0' and '%1'",
       (StringRef, StringRef))
 
+WARNING(warn_ignore_embed_bitcode, none,
+        "ignoring -embed-bitcode since no object file is being generated", ())
+
 #ifndef DIAG_NO_UNDEF
 # if defined(DIAG)
 #  undef DIAG

lib/Driver/Driver.cpp

@@ -448,6 +448,16 @@ static bool populateOutOfDateMap(InputInfoMap &map, StringRef argsHashStr,
   }
 }
 
+// warn if -embed-bitcode is set and the output type is not an object
+static void validateEmbedBitcode(DerivedArgList &Args, OutputInfo &OI,
+                                 DiagnosticEngine &Diags) {
+  if (Args.hasArg(options::OPT_embed_bitcode) &&
+      OI.CompilerOutputType != types::TY_Object) {
+    Diags.diagnose(SourceLoc(), diag::warn_ignore_embed_bitcode);
+    Args.eraseArg(options::OPT_embed_bitcode);
+  }
+}
+
 std::unique_ptr<Compilation> Driver::buildCompilation(
     ArrayRef<const char *> Args) {
   llvm::PrettyStackTraceString CrashInfo("Compilation construction");
@@ -535,6 +545,8 @@ std::unique_ptr<Compilation> Driver::buildCompilation(
 
   assert(OI.CompilerOutputType != types::ID::TY_INVALID &&
          "buildOutputInfo() must set a valid output type!");
+  
+  validateEmbedBitcode(*TranslatedArgList, OI, Diags);
 
   if (OI.CompilerMode == OutputInfo::Mode::REPL)
     // REPL mode expects no input files, so suppress the error.

test/Driver/embed-bitcode.swift

@@ -77,3 +77,15 @@
 // CHECK-LIB: -embed-bitcode
 // CHECK-LIB: -disable-llvm-optzns
 // CHECK-LIB-NOT: swift -frontend
+
+// RUN: %target-swiftc_driver -embed-bitcode -emit-module %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// RUN: %target-swiftc_driver -embed-bitcode -emit-module-path a.swiftmodule %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// RUN: %target-swiftc_driver -embed-bitcode -emit-sib %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// RUN: %target-swiftc_driver -embed-bitcode -emit-sibgen %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// RUN: %target-swiftc_driver -embed-bitcode -emit-sil %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// RUN: %target-swiftc_driver -embed-bitcode -emit-silgen %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// RUN: %target-swiftc_driver -embed-bitcode -emit-ir %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// RUN: %target-swiftc_driver -embed-bitcode -emit-bc %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// RUN: %target-swiftc_driver -embed-bitcode -emit-assembly %s 2>&1 -### | %FileCheck %s -check-prefix=WARN-EMBED-BITCODE
+// WARN-EMBED-BITCODE: warning: ignoring -embed-bitcode since no object file is being generated
+// WARN-EMBED-BITCODE-NOT: -embed-bitcode