Add test cases for Span-providing properties.

test/SILOptimizer/lifetime_dependence/stdlib_span.swift

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+// RUN: %target-swift-frontend %s -emit-sil \
+// RUN:   -o /dev/null \
+// RUN:   -verify \
+// RUN:   -sil-verify-all \
+// RUN:   -module-name test \
+// RUN:   -disable-access-control \
+// RUN:   -enable-experimental-feature LifetimeDependence \
+// RUN:   -enable-experimental-feature Span
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: swift_feature_LifetimeDependence
+// REQUIRES: swift_feature_Span
+
+// Test dependencies on the standard library Span APIs.
+
+// =============================================================================
+// Span-providing properties
+// =============================================================================
+
+extension UnsafeRawBufferPointer {
+  @available(SwiftStdlib 6.1, *)
+  public var storage: RawSpan {
+    @lifetime(borrow self)
+    get {
+      let span = RawSpan(_unsafeBytes: self)
+      return _overrideLifetime(span, borrowing: self)
+    }
+  }
+}
+
+@available(SwiftStdlib 6.1, *)
+func read(_ span: RawSpan) {}
+
+@available(SwiftStdlib 6.1, *)
+func testUBPStorage(ubp: UnsafeRawBufferPointer) {
+  // 'span' is valid within the lexical scope of variable 'ubp', which is the entire function.
+  let span = ubp.storage
+  read(span)
+}
+
+@available(SwiftStdlib 6.1, *)
+@lifetime(borrow ubp)
+func testUBPStorageReturn(ubp: UnsafeRawBufferPointer) -> RawSpan {
+  // 'storage' can be returned since the function's return value also has a dependence on 'ubp'.
+  return ubp.storage
+}
+
+@available(SwiftStdlib 6.1, *)
+@lifetime(borrow ubp)
+func testUBPStorageCopy(ubp: UnsafeRawBufferPointer) -> RawSpan {
+  let localBuffer = ubp
+  return localBuffer.storage // expected-error {{lifetime-dependent value escapes its scope}}
+                             // expected-note  @-2{{it depends on the lifetime of variable 'localBuffer'}}
+                             // expected-note  @-2{{this use causes the lifetime-dependent value to escape}}
+}
+
+@available(SwiftStdlib 6.1, *)
+func testUBPStorageEscape(array: [Int64]) {
+  var span = RawSpan()
+  array.withUnsafeBytes {
+    span = $0.storage // expected-error {{lifetime-dependent value escapes its scope}}
+                      // expected-note  @-2{{it depends on the lifetime of argument '$0'}}
+                      // expected-note  @-2{{this use causes the lifetime-dependent value to escape}}
+  }
+  read(span)
+}