[cxx-interop] Make borrowing specifiers more precise

We do not need to borrow from view objects passed by value but we need
to borrow from owners taken by const reference regardless of whether it
was annotated using lifetimebound or lifetime_capture_by.

Author: Gabor Horvath

lib/ClangImporter/ImportType.cpp

@@ -2687,14 +2687,18 @@ static ParamDecl *getParameterInfo(ClangImporter::Implementation *impl,
     }
   }
 
+  // Parameters of type const T& imported as T, make sure we borrow from them
+  // when they have lifetime annotations.
+  bool isBorrowing = (param->getAttr<clang::LifetimeBoundAttr>() ||
+                      param->getAttr<clang::LifetimeCaptureByAttr>()) &&
+                     param->getType()->isReferenceType();
   // Foreign references are already references so they don't need to be passed
   // as inout.
   paramInfo->setSpecifier(
       isConsuming ? ParamSpecifier::Consuming
                   : (isInOut ? ParamSpecifier::InOut
-                             : (param->getAttr<clang::LifetimeBoundAttr>()
-                                    ? ParamSpecifier::Borrowing
-                                    : ParamSpecifier::Default)));
+                             : (isBorrowing ? ParamSpecifier::Borrowing
+                                            : ParamSpecifier::Default)));
   paramInfo->setInterfaceType(swiftParamTy);
   impl->recordImplicitUnwrapForDecl(paramInfo, isParamTypeImplicitlyUnwrapped);
 

test/Interop/Cxx/class/nonescapable-lifetimebound.swift

@@ -111,9 +111,9 @@ CaptureView getCaptureView(const Owner& owner [[clang::lifetimebound]]) {
 // CHECK: sil [clang getViewFromEither] {{.*}} : $@convention(c) (@in_guaranteed Owner, @in_guaranteed Owner) -> @lifetime(borrow 0, borrow 1) @owned View
 // CHECK: sil [clang Owner.handOutView] {{.*}} : $@convention(cxx_method) (@in_guaranteed Owner) -> @lifetime(borrow 0) @owned View
 // CHECK: sil [clang Owner.handOutView2] {{.*}} : $@convention(cxx_method) (View, @in_guaranteed Owner) -> @lifetime(borrow 1) @owned View
-// CHECK: sil [clang getViewFromEither] {{.*}} : $@convention(c) (@guaranteed View, @guaranteed View) -> @lifetime(copy 0, copy 1) @owned View
+// CHECK: sil [clang getViewFromEither] {{.*}} : $@convention(c) (View, View) -> @lifetime(copy 0, copy 1) @owned View
 // CHECK: sil [clang View.init] {{.*}} : $@convention(c) () -> @lifetime(immortal) @out View
-// CHECK: sil [clang OtherView.init] {{.*}} : $@convention(c) (@guaranteed View) -> @lifetime(copy 0) @out OtherView
+// CHECK: sil [clang OtherView.init] {{.*}} : $@convention(c) (View) -> @lifetime(copy 0) @out OtherView
 // CHECK: sil [clang returnsImmortal] {{.*}} : $@convention(c) () -> @lifetime(immortal) @owned View
 // CHECK: sil [clang copyView] {{.*}} : $@convention(c) (View, @lifetime(copy 0) @inout View) -> ()
 // CHECK: sil [clang getCaptureView] {{.*}} : $@convention(c) (@in_guaranteed Owner) -> @lifetime(borrow 0) @owned CaptureView

test/Interop/Cxx/stdlib/Inputs/std-span.h

@@ -56,6 +56,13 @@ inline SpanOfInt initSpan(int arr[], size_t size) {
 
 inline struct SpanBox getStructSpanBox() { return {iarray, iarray, sarray, sarray}; }
 
+struct CaptureByReference {
+    void set(const std::vector<int>& x [[clang::lifetime_capture_by(this)]]) { 
+        this->x = ConstSpanOfInt(x.data(), x.size());
+    };
+    ConstSpanOfInt x;
+};
+
 inline void funcWithSafeWrapper(ConstSpanOfInt s [[clang::noescape]]) {}
 
 inline ConstSpanOfInt funcWithSafeWrapper2(ConstSpanOfInt s

test/Interop/Cxx/stdlib/std-span-interface.swift

@@ -14,11 +14,12 @@ import StdSpan
 #endif
 import CxxStdlib
 
+// CHECK:      mutating func set(_ x: borrowing std.{{.*}}vector<CInt, std.{{.*}}allocator<CInt>>)
 // CHECK:      func funcWithSafeWrapper(_ s: ConstSpanOfInt)
-// CHECK-NEXT: func funcWithSafeWrapper2(_ s: borrowing ConstSpanOfInt) -> ConstSpanOfInt
+// CHECK-NEXT: func funcWithSafeWrapper2(_ s: ConstSpanOfInt) -> ConstSpanOfInt
 // CHECK-NEXT: func funcWithSafeWrapper3(_ v: borrowing VecOfInt) -> ConstSpanOfInt
 // CHECK-NEXT: @_alwaysEmitIntoClient public func funcWithSafeWrapper(_ s: Span<CInt>)
 // CHECK-NEXT: @lifetime(s)
-// CHECK-NEXT: @_alwaysEmitIntoClient public func funcWithSafeWrapper2(_ s: borrowing Span<CInt>) -> Span<CInt>
+// CHECK-NEXT: @_alwaysEmitIntoClient public func funcWithSafeWrapper2(_ s: Span<CInt>) -> Span<CInt>
 // CHECK-NEXT: @lifetime(borrow v)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func funcWithSafeWrapper3(_ v: borrowing VecOfInt) -> Span<CInt>