[Sema] Enable require explicit availability by default for public modules

rdar://99929744

Author: xymus

lib/Frontend/CompilerInvocation.cpp

@@ -728,7 +728,8 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
                      diagLevel);
     }
   } else if (Args.getLastArg(OPT_require_explicit_availability,
-                             OPT_require_explicit_availability_target)) {
+                             OPT_require_explicit_availability_target) ||
+             Opts.LibraryLevel == LibraryLevel::API) {
     Opts.RequireExplicitAvailability = DiagnosticBehavior::Warning;
   }
 

test/attr/require_explicit_availability.swift

@@ -10,6 +10,17 @@
 // RUN:   -target %target-cpu-apple-macosx10.10 -require-explicit-availability=warn \
 // RUN:   -require-explicit-availability-target "macOS 10.10"
 
+/// Using -library-level api defaults to enabling warnings, without fixits.
+// RUN: sed -e "s/}} {{.*/}}/" < %s > %t/NoFixits.swift
+// RUN: %target-swift-frontend -typecheck -parse-as-library -verify %t/NoFixits.swift \
+// RUN:   -target %target-cpu-apple-macosx10.10 -library-level api
+
+/// Explicitly disable the diagnostic.
+// RUN: sed -e 's/xpected-warning/not-something-expected/' < %s > %t/None.swift
+// RUN: %target-swift-frontend -typecheck -parse-as-library -verify %t/None.swift \
+// RUN:   -target %target-cpu-apple-macosx10.10 -require-explicit-availability=ignore \
+// RUN:   -require-explicit-availability-target "macOS 10.10" -library-level api
+
 /// Upgrade the diagnostic to an error.
 // RUN: sed -e "s/xpected-warning/xpected-error/" < %s > %t/Errors.swift
 // RUN: %target-swift-frontend -typecheck -parse-as-library -verify %t/Errors.swift \