Fix Issue 12118 - Modify immutable data using throw (#14706)

* Fix Issue 12118 - Modify immutable data using throw

* Change immutable test to const

* Deprecate throwing any qualified type

* Allow throw shared as std.concurrency does that

* Use static this instead of static const for test

* Only allow single shared qualifier or none

* Add changelog

* Disallow throwing shared objects too

* Update changelog/dmd.throw-qualifier.dd

Co-authored-by: Razvan Nitu <razvan.nitu1305@gmail.com>

---------

Co-authored-by: Razvan Nitu <razvan.nitu1305@gmail.com>

changelog/dmd.throw-qualifier.dd

@@ -0,0 +1,11 @@
+Throwing qualified objects is now deprecated
+
+Previously, an `immutable`, `const`, `inout` or `shared` exception could be
+thrown and then caught in an unqualified `catch (Exception e)` clause.
+That breaks type safety.
+Throwing a qualified object is now deprecated. This helps to prevent
+possible mutation of an immutable object in a `catch` clause.
+
+The runtime also modifies a thrown object (e.g. to contain a stack
+trace) which can violate `const` or `immutable` objects. Throwing
+qualified objects has been deprecated for this reason also.

compiler/src/dmd/statementsem.d

@@ -3796,7 +3796,13 @@ package (dmd) extern (C++) final class StatementSemanticVisitor : Visitor
         exp = checkGC(sc, exp);
         if (exp.op == EXP.error)
             return false;
-
+        if (!exp.type.isNaked())
+        {
+            // @@@DEPRECATED_2.112@@@
+            // Deprecated in 2.102, change into an error & return false in 2.112
+            exp.loc.deprecation("cannot throw object of qualified type `%s`", exp.type.toChars());
+            //return false;
+        }
         checkThrowEscape(sc, exp, false);
 
         ClassDeclaration cd = exp.type.toBasetype().isClassHandle();

compiler/test/fail_compilation/ice10651.d

@@ -1,7 +1,9 @@
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/ice10651.d(11): Error: can only throw class objects derived from `Throwable`, not type `int*`
+fail_compilation/ice10651.d(13): Error: can only throw class objects derived from `Throwable`, not type `int*`
+fail_compilation/ice10651.d(19): Deprecation: cannot throw object of qualified type `immutable(Exception)`
+fail_compilation/ice10651.d(20): Deprecation: cannot throw object of qualified type `const(Dummy)`
 ---
 */
 
@@ -10,3 +12,20 @@ void main()
     alias T = int;
     throw new T();  // ICE
 }
+
+void f()
+{
+    immutable c = new Exception("");
+    if (c) throw c;
+    throw new const Dummy([]);
+}
+
+class Dummy: Exception
+{
+    int[] data;
+    @safe pure nothrow this(immutable int[] data) immutable
+    {
+        super("Dummy");
+        this.data = data;
+    }
+}

compiler/test/runnable/class_destructors.d

@@ -154,7 +154,13 @@ void testDeleteWithoutCpp()
 
 class ThrowingChildD : ChildD
 {
-	static immutable ex = new Exception("STOP");
+	static Exception ex;
+
+	static this()
+	{
+		ex = new Exception("STOP");
+	}
+
 	~this()
 	{
 		throw ex;

compiler/test/runnable/eh2.d

@@ -24,7 +24,7 @@ class Abc : Throwable
     {
         printf("foo 1\n");
         x |= 4;
-        throw this;
+        throw cast() this;
         printf("foo 2\n");
         x |= 8;
     }