[Driver] Infer simulator-ness for iOS/tvOS/watchOS.

Localize the hack to infer simulator-ness of the target in the driver
itself, when it first processes the target. Emit a warning about the
missing "-simulator" and correct the triple immediately.

This gives a longer grace period for tools that might still not pass
through the simulator environment, while narrowing the hack.

Author: DougGregor

include/swift/AST/DiagnosticsDriver.def

@@ -84,6 +84,9 @@ ERROR(error_unexpected_input_file,none,
 
 ERROR(error_unknown_target,none,
       "unknown target '%0'", (StringRef))
+WARNING(warning_inferred_simulator_target,none,
+      "inferring simulator environment for target '%0'; "
+      "use '-target %1' instead", (StringRef, StringRef))
 
 ERROR(error_framework_bridging_header,none,
       "using bridging headers with framework targets is unsupported", ())

lib/Driver/Driver.cpp

@@ -264,17 +264,35 @@ static void validateArgs(DiagnosticEngine &diags, const ArgList &args,
 std::unique_ptr<ToolChain>
 Driver::buildToolChain(const llvm::opt::InputArgList &ArgList) {
 
-  if (const Arg *A = ArgList.getLastArg(options::OPT_target))
+  if (const Arg *A = ArgList.getLastArg(options::OPT_target)) {
     DefaultTargetTriple = llvm::Triple::normalize(A->getValue());
+  }
 
-  const llvm::Triple target(DefaultTargetTriple);
+  llvm::Triple target(DefaultTargetTriple);
 
   switch (target.getOS()) {
-  case llvm::Triple::Darwin:
-  case llvm::Triple::MacOSX:
   case llvm::Triple::IOS:
   case llvm::Triple::TvOS:
-  case llvm::Triple::WatchOS: {
+  case llvm::Triple::WatchOS:
+    // Backward compatibility hack: infer "simulator" environment for x86
+    // iOS/tvOS/watchOS.
+    if (!target.isSimulatorEnvironment() &&
+        (target.getArch() == llvm::Triple::x86 ||
+         target.getArch() == llvm::Triple::x86_64) &&
+        !tripleIsMacCatalystEnvironment(target)) {
+      // Set the simulator environment.
+      target.setEnvironment(llvm::Triple::EnvironmentType::Simulator);
+
+      auto newTargetTriple = target.normalize();
+      Diags.diagnose(SourceLoc(), diag::warning_inferred_simulator_target,
+                     DefaultTargetTriple, newTargetTriple);
+
+      DefaultTargetTriple = newTargetTriple;
+    }
+    LLVM_FALLTHROUGH;
+
+  case llvm::Triple::Darwin:
+  case llvm::Triple::MacOSX: {
     Optional<llvm::Triple> targetVariant;
     if (const Arg *A = ArgList.getLastArg(options::OPT_target_variant))
       targetVariant = llvm::Triple(llvm::Triple::normalize(A->getValue()));

test/Driver/infer-simulator.swift

@@ -0,0 +1,13 @@
+// Test the inference of the "simulator" environment within the driver.
+
+// RUN: %swiftc_driver -driver-print-jobs -target x86_64-apple-ios11.0 %s > %t.simple.txt 2>&1
+// RUN: %FileCheck -check-prefix WARN_IOS_SIMULATOR %s < %t.simple.txt
+// WARN_IOS_SIMULATOR:  warning: inferring simulator environment for target 'x86_64-apple-ios11.0'; use '-target x86_64-apple-ios11.0-simulator' instead
+
+// RUN: %swiftc_driver -driver-print-jobs -target x86_64-apple-tvos10.0 %s > %t.simple.txt 2>&1
+// RUN: %FileCheck -check-prefix WARN_TVOS_SIMULATOR %s < %t.simple.txt
+// WARN_TVOS_SIMULATOR: inferring simulator environment for target 'x86_64-apple-tvos10.0'; use '-target x86_64-apple-tvos10.0-simulator' instead
+
+// RUN: %swiftc_driver -driver-print-jobs -target i386-apple-watchos4.0 %s > %t.simple.txt 2>&1
+// RUN: %FileCheck -check-prefix WARN_WATCHOS_SIMULATOR %s < %t.simple.txt
+// WARN_WATCHOS_SIMULATOR: warning: inferring simulator environment for target 'i386-apple-watchos4.0'; use '-target i386-apple-watchos4.0-simulator' instead