Fix Bugzilla 24631 - Pointer cast allows changing @System field in @safe

 code

compiler/src/dmd/safe.d

@@ -231,15 +231,6 @@ bool isSafeCast(Expression e, Type tfrom, Type tto, ref string msg)
  return false;
  }
 
- // For bool, only 0 and 1 are safe values
- // Runtime array cast reinterprets data
- if (ttobn.ty == Tbool && tfromn.ty != Tbool && e.op != EXP.arrayLiteral)
- msg = "Source element may have bytes which are not 0 or 1";
- // Can't alias a bool pointer with a non-bool pointer
- if (ttobn.ty != Tbool && tfromn.ty == Tbool && ttobn.isMutable() &&
- e.op != EXP.arrayLiteral)
- msg = "Target element could be assigned a byte which is not 0 or 1";
-
  // If the struct is opaque we don't know about the struct members then the cast becomes unsafe
  if (ttobn.ty == Tstruct && !(cast(TypeStruct)ttobn).sym.members)
  {
@@ -252,6 +243,22 @@ bool isSafeCast(Expression e, Type tfrom, Type tto, ref string msg)
  return false;
  }
 
+ if (e.op != EXP.arrayLiteral)
+ {
+ // For bool, only 0 and 1 are safe values
+ // Runtime array cast reinterprets data
+ if (ttobn.ty == Tbool && tfromn.ty != Tbool)
+ msg = "Source element may have bytes which are not 0 or 1";
+ else if (ttobn.hasUnsafeBitpatterns())
+ msg = "Target element type has unsafe bit patterns";
+
+ // Can't alias a bool pointer with a non-bool pointer
+ if (ttobn.ty != Tbool && tfromn.ty == Tbool && ttobn.isMutable())
+ msg = "Target element could be assigned a byte which is not 0 or 1";
+ else if (tfromn.hasUnsafeBitpatterns() && ttobn.isMutable())
+ msg = "Source element type has unsafe bit patterns and target element type is mutable";
+ }
+
  const frompointers = tfromn.hasPointers();
  const topointers = ttobn.hasPointers();
 

compiler/test/fail_compilation/system_ptr_cast.d

@@ -0,0 +1,25 @@
+/*
+REQUIRED_ARGS: -preview=dip1000 -de
+TEST_OUTPUT:
+---
+fail_compilation/system_ptr_cast.d(20): Deprecation: cast from `S*` to `int*` not allowed in safe code
+fail_compilation/system_ptr_cast.d(20): Source element type has unsafe bit patterns and target element type is mutable
+fail_compilation/system_ptr_cast.d(24): Deprecation: cast from `int*` to `S*` not allowed in safe code
+fail_compilation/system_ptr_cast.d(24): Target element type has unsafe bit patterns
+---
+*/
+
+struct S
+{
+ @system int i;
+}
+
+void main() @safe
+{
+ S s;
+ auto p = cast(int*) &s;
+ *p = 8;
+
+ int i = 8;
+ auto ps = cast(S*) &i;
+}