[ClangImporter] Don't import C function pointer typedefs as bridged

We don't get to bridge C functions usually, so the typedef is more
useful in its unbridged form. Undoes a change by John in 0e89efa.

Author: jrose-apple

lib/ClangImporter/ImporterImpl.h

@@ -191,10 +191,13 @@ enum class Bridgeability {
   Full
 };
 
+/// Controls whether a typedef for \p type should name the fully-bridged Swift
+/// type or the original Clang type.
+///
+/// In either case we end up losing sugar at some uses sites, so this is more
+/// about what the right default is.
 static inline Bridgeability getTypedefBridgeability(clang::QualType type) {
-  return (type->isBlockPointerType() || type->isFunctionType())
-            ? Bridgeability::Full
-            : Bridgeability::None;
+  return type->isBlockPointerType() ? Bridgeability::Full : Bridgeability::None;
 }
 
 /// \brief Describes the kind of the C type that can be mapped to a stdlib

test/ClangImporter/Inputs/custom-modules/ObjCParseExtras.h

@@ -209,3 +209,6 @@ typedef NSArray<NSString *> *NSStringArray;
 @interface BridgedTypedefs : NSObject
 @property (readonly,nonnull) NSArray<NSStringArray> *arrayOfArrayOfStrings;
 @end
+
+typedef NSString * _Nonnull (*FPTypedef)(NSString * _Nonnull);
+extern FPTypedef _Nonnull getFP(void);

test/ClangImporter/objc_parse.swift

@@ -643,3 +643,9 @@ func testTypeAndValue() {
 func testBridgedTypedef(bt: BridgedTypedefs) {
   let _: Int = bt.arrayOfArrayOfStrings // expected-error{{'[[String]]'}}
 }
+
+func testBridgeFunctionPointerTypedefs(fptrTypedef: FPTypedef) {
+  // See also print_clang_bool_bridging.swift.
+  let _: Int = fptrTypedef // expected-error{{'@convention(c) (String) -> String'}}
+  let _: Int = getFP() // expected-error{{'@convention(c) (String) -> String'}}
+}