[Driver] Disallow -autolink-force-load with -incremental

6af333f changed the implementation of -autolink-force-load to only
generate one symbol, but the /placement/ of that one symbol depends on
the order of input files, and -incremental supports adding a file
without rebuilding all other files. We don't have any need for these
two to play nice together right now, so just disallow it.

Author: jrose-apple

include/swift/AST/DiagnosticsDriver.def

@@ -126,6 +126,9 @@ ERROR(error_input_changed_during_build,none,
 ERROR(error_conflicting_options, none,
       "conflicting options '%0' and '%1'",
       (StringRef, StringRef))
+ERROR(error_option_not_supported, none,
+      "'%0' is not supported with '%1'",
+      (StringRef, StringRef))
 
 WARNING(warn_ignore_embed_bitcode, none,
         "ignoring -embed-bitcode since no object file is being generated", ())

lib/Driver/Driver.cpp

@@ -119,6 +119,7 @@ ArrayRef<const char *> Driver::getArgsWithoutProgramNameAndDriverMode(
   return Args;
 }
 
+/// Perform miscellaneous early validation of arguments.
 static void validateArgs(DiagnosticEngine &diags, const ArgList &Args) {
   if (Args.hasArgNoClaim(options::OPT_import_underlying_module) &&
       Args.hasArgNoClaim(options::OPT_import_objc_header)) {
@@ -199,6 +200,18 @@ static void validateArgs(DiagnosticEngine &diags, const ArgList &Args) {
       diags.diagnose(SourceLoc(), diag::invalid_conditional_compilation_flag,
                      name);
   }
+
+  if (auto *forceLoadArg = Args.getLastArg(options::OPT_autolink_force_load)) {
+    if (auto *incrementalArg = Args.getLastArg(options::OPT_incremental)) {
+      // Note: -incremental can itself be overridden by other arguments later
+      // on, but since -autolink-force-load is a rare and not-really-recommended
+      // option it's not worth modeling that complexity here (or moving the
+      // check somewhere else).
+      diags.diagnose(SourceLoc(), diag::error_option_not_supported,
+                     forceLoadArg->getSpelling(),
+                     incrementalArg->getSpelling());
+    }
+  }
 }
 
 std::unique_ptr<ToolChain>

test/Driver/options.swift

@@ -129,3 +129,7 @@
 // RUN: %swiftc_driver -driver-print-jobs -assume-single-threaded %s | %FileCheck -check-prefix=ASSUME_SINGLE_THREADED %s
 // ASSUME_SINGLE_THREADED: swift
 // ASSUME_SINGLE_THREADED: -frontend {{.*}} -assume-single-threaded
+
+// RUN: not %swiftc_driver -incremental -autolink-force-load %s 2>&1 | %FileCheck -check-prefix=AUTOLINK_FORCE_LOAD %s
+// RUN: not %swiftc_driver -autolink-force-load -incremental %s 2>&1 | %FileCheck -check-prefix=AUTOLINK_FORCE_LOAD %s
+// AUTOLINK_FORCE_LOAD: error: '-autolink-force-load' is not supported with '-incremental'