Put warnings about unsafe constructs into a new diagnostic group Unsafe

include/swift/AST/DiagnosticGroups.def

@@ -23,6 +23,7 @@
 GROUP(no_group, "")
 
 GROUP(DeprecatedDeclaration, "DeprecatedDeclaration.md")
+GROUP(Unsafe, "Unsafe.md")
 GROUP(UnknownWarningGroup, "UnknownWarningGroup.md")
 
 #define UNDEFINE_DIAGNOSTIC_GROUPS_MACROS

include/swift/AST/DiagnosticsSema.def

@@ -8053,24 +8053,24 @@ NOTE(sending_function_result_with_sending_param_note, none,
 //------------------------------------------------------------------------------
 ERROR(unsafe_attr_disabled,none,
       "attribute requires '-enable-experimental-feature AllowUnsafeAttribute'", ())
-WARNING(override_safe_withunsafe,none,
+GROUPED_WARNING(override_safe_withunsafe,Unsafe,none,
       "override of safe %0 with unsafe %0", (DescriptiveDeclKind))
-WARNING(witness_unsafe,none,
+GROUPED_WARNING(witness_unsafe,Unsafe,none,
      "unsafe %0 %1 cannot satisfy safe requirement",
       (DescriptiveDeclKind, DeclName))
-WARNING(type_witness_unsafe,none,
+GROUPED_WARNING(type_witness_unsafe,Unsafe,none,
       "unsafe type %0 cannot satisfy safe associated type %1",
       (Type, DeclName))
-WARNING(unchecked_conformance_is_unsafe,none,
+GROUPED_WARNING(unchecked_conformance_is_unsafe,Unsafe,none,
       "@unchecked conformance involves unsafe code", ())
-WARNING(unowned_unsafe_is_unsafe,none,
+GROUPED_WARNING(unowned_unsafe_is_unsafe,Unsafe,none,
       "unowned(unsafe) involves unsafe code", ())
-WARNING(nonisolated_unsafe_is_unsafe,none,
+GROUPED_WARNING(nonisolated_unsafe_is_unsafe,Unsafe,none,
       "nonisolated(unsafe) involves unsafe code", ())
-WARNING(reference_to_unsafe_decl,none,
+GROUPED_WARNING(reference_to_unsafe_decl,Unsafe,none,
       "%select{reference|call}0 to unsafe %kindbase1",
       (bool, const ValueDecl *))
-WARNING(reference_to_unsafe_typed_decl,none,
+GROUPED_WARNING(reference_to_unsafe_typed_decl,Unsafe,none,
       "%select{reference|call}0 to %kindbase1 involves unsafe type %2",
       (bool, const ValueDecl *, Type))
 NOTE(unsafe_decl_here,none,

test/Unsafe/unsafe.swift

@@ -1,7 +1,7 @@
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend -emit-module-path %t/unsafe_swift_decls.swiftmodule %S/Inputs/unsafe_swift_decls.swift -enable-experimental-feature AllowUnsafeAttribute
 
-// RUN: %target-typecheck-verify-swift -enable-experimental-feature AllowUnsafeAttribute -enable-experimental-feature WarnUnsafe -I %t
+// RUN: %target-typecheck-verify-swift -enable-experimental-feature AllowUnsafeAttribute -enable-experimental-feature WarnUnsafe -I %t -print-diagnostic-groups
 
 // Make sure everything compiles without error when unsafe code is allowed.
 // RUN: %target-swift-frontend -typecheck -enable-experimental-feature AllowUnsafeAttribute %s -I %t
@@ -20,7 +20,7 @@ protocol P {
 }
 
 struct XP: P {
-  @unsafe func f() { } // expected-warning{{unsafe instance method 'f()' cannot satisfy safe requirement}}
+  @unsafe func f() { } // expected-warning{{unsafe instance method 'f()' cannot satisfy safe requirement [Unsafe]}}
   @unsafe func g() { }
 }
 

userdocs/diagnostic_groups/Unsafe.md

@@ -0,0 +1,25 @@
+# Unsafe code wanings (`Unsafe`)
+
+
+This diagnostic group includes warnings that identify the use of unsafe language constructs and library APIs. Example warnings include:
+
+- Use of an unsafe language feature:
+  ```swift
+  // warning: unowned(unsafe) involves unsafe code
+  unowned(unsafe) var parentNode: TreeNode<T>
+  ```
+- Use of a function or type annotated with `@unsafe`:
+  ```swift
+  // warning: reference to unsafe generic struct 'UnsafeMutablePointer'
+  func getPointee<T>(_ pointer: UnsafeMutablePointer<Int>, as type: T.Type) -> T {
+    // warning: call to unsafe global function 'unsafeBitCast'
+    return unsafeBitCast(pointer.pointee, to: type)
+  }
+  ```
+- Use of a function involving an `@unsafe` type:
+  ```swift
+  func evilMalloc(size: Int) -> Int {
+    // warning: call to global function 'malloc' involves unsafe type 'UnsafeMutableRawPointer'
+    return Int(bitPattern: malloc(size))
+  }
+  ```