fix Issue 15862 - allocating storage in pure functions should not res…

src/mtype.d

@@ -6456,6 +6456,7 @@ extern (C++) final class TypeFunction : TypeNext
     }
 
     /********************************************
+     * Set 'purity' field of 'this'.
      * Do this lazily, as the parameter types might be forward referenced.
      */
     void purityLevel()
@@ -6464,73 +6465,94 @@ extern (C++) final class TypeFunction : TypeNext
         if (tf.purity != PUREfwdref)
             return;
 
-        /* Evaluate what kind of purity based on the modifiers for the parameters
+        /* Determine purity level based on mutability of t
+         * and whether it is a 'ref' type or not.
          */
-        tf.purity = PUREstrong; // assume strong until something weakens it
-
-        size_t dim = Parameter.dim(tf.parameters);
-        if (!dim)
-            return;
-        for (size_t i = 0; i < dim; i++)
+        static PURE purityOfType(bool isref, Type t)
         {
-            Parameter fparam = Parameter.getNth(tf.parameters, i);
-            Type t = fparam.type;
-            if (!t)
-                continue;
-
-            if (fparam.storageClass & (STClazy | STCout))
-            {
-                tf.purity = PUREweak;
-                break;
-            }
-            if (fparam.storageClass & STCref)
+            if (isref)
             {
                 if (t.mod & MODimmutable)
-                    continue;
+                    return PUREstrong;
                 if (t.mod & (MODconst | MODwild))
-                {
-                    tf.purity = PUREconst;
-                    continue;
-                }
-                tf.purity = PUREweak;
-                break;
+                    return PUREconst;
+                return PUREweak;
             }
 
             t = t.baseElemOf();
-            if (!t.hasPointers())
-                continue;
-            if (t.mod & MODimmutable)
-                continue;
+
+            if (!t.hasPointers() || t.mod & MODimmutable)
+                return PUREstrong;
 
             /* Accept immutable(T)[] and immutable(T)* as being strongly pure
              */
             if (t.ty == Tarray || t.ty == Tpointer)
             {
                 Type tn = t.nextOf().toBasetype();
                 if (tn.mod & MODimmutable)
-                    continue;
+                    return PUREstrong;
                 if (tn.mod & (MODconst | MODwild))
-                {
-                    tf.purity = PUREconst;
-                    continue;
-                }
+                    return PUREconst;
             }
 
             /* The rest of this is too strict; fix later.
              * For example, the only pointer members of a struct may be immutable,
              * which would maintain strong purity.
+             * (Just like for dynamic arrays and pointers above.)
              */
             if (t.mod & (MODconst | MODwild))
-            {
-                tf.purity = PUREconst;
+                return PUREconst;
+
+            /* Should catch delegates and function pointers, and fold in their purity
+             */
+            return PUREweak;
+        }
+
+        purity = PUREstrong; // assume strong until something weakens it
+
+        /* Evaluate what kind of purity based on the modifiers for the parameters
+         */
+        const dim = Parameter.dim(tf.parameters);
+    Lloop: foreach (i; 0 .. dim)
+        {
+            Parameter fparam = Parameter.getNth(tf.parameters, i);
+            Type t = fparam.type;
+            if (!t)
                 continue;
+
+            if (fparam.storageClass & (STClazy | STCout))
+            {
+                purity = PUREweak;
+                break;
             }
+            switch (purityOfType((fparam.storageClass & STCref) != 0, t))
+            {
+                case PUREweak:
+                    purity = PUREweak;
+                    break Lloop; // since PUREweak, no need to check further
 
-            /* Should catch delegates and function pointers, and fold in their purity
+                case PUREconst:
+                    purity = PUREconst;
+                    continue;
+
+                case PUREstrong:
+                    continue;
+
+                default:
+                    assert(0);
+            }
+        }
+
+        if (purity > PUREweak && tf.nextOf())
+        {
+            /* Adjust purity based on mutability of return type.
+             * https://issues.dlang.org/show_bug.cgi?id=15862
              */
-            tf.purity = PUREweak; // err on the side of too strict
-            break;
+            const purity2 = purityOfType(tf.isref, tf.nextOf());
+            if (purity2 < purity)
+                purity = purity2;
         }
+        tf.purity = purity;
     }
 
     /********************************************

test/runnable/test15862.d

@@ -0,0 +1,66 @@
+// https://issues.dlang.org/show_bug.cgi?id=15862
+
+/*
+PERMUTE_ARGS:
+REQUIRED_ARGS: -O -release
+*/
+
+
+int* p() pure nothrow {return new int;}
+int[] a() pure nothrow {return [0];}
+Object o() pure nothrow {return new Object;}
+
+immutable(int)* pn() pure nothrow {return new int;}
+immutable(int)[] an() pure nothrow {return [0];}
+immutable(Object) on() pure nothrow {return new Object;}
+
+auto pa() pure nothrow {return new int;}
+auto pb() pure nothrow {return cast(immutable(int)*)(new int);}
+
+void main()
+{
+    {
+        int* p1 = p();
+        int* p2 = p();
+
+        if (p1 is p2) assert(0);
+
+        int[] a1 = a();
+        int[] a2 = a();
+
+        if (a1 is a2) assert(0);
+
+        Object o1 = o();
+        Object o2 = o();
+
+        if (o1 is o2) assert(0);
+    }
+    {
+        auto p1 = pn();
+        auto p2 = pn();
+
+        if (p1 !is p2) assert(0);
+
+        auto a1 = an();
+        auto a2 = an();
+
+        if (a1 !is a2) assert(0);
+
+        auto o1 = on();
+        auto o2 = on();
+
+        if (o1 !is o2) assert(0);
+    }
+    {
+        auto p1 = pa();
+        auto p2 = pa();
+
+        if (p1 is p2) assert(0);
+    }
+    {
+        auto p1 = pb();
+        auto p2 = pb();
+
+        if (p1 !is p2) assert(0);
+    }
+}