Fixes Issue 8777

Add test-cases for const/immutable diagnostics.
Use MODtoBuffer for output.

src/expression.c

@@ -1842,12 +1842,9 @@ void Expression::checkModifiable(Scope *sc)
             }
             else
             {
-                const char *p =
-                    type->isImmutable() ? "immutable" :
-                    type->isConst() ? "const" :
-                    type->isWild() ? "wild" : NULL;
-                assert(p);
-                error("cannot modify %s expression %s", p, toChars());
+                OutBuffer buf;
+                MODtoBuffer(&buf, type->mod);
+                error("cannot modify %s expression %s", buf.toChars(), toChars());
             }
         }
     }
@@ -7580,14 +7577,9 @@ Expression *CallExp::resolveUFCS(Scope *sc)
                 return new ErrorExp();
             }
             if (!e->type->isMutable())
-            {   const char *p = NULL;
-                if (e->type->isConst())
-                    p = "const";
-                else if (e->type->isImmutable())
-                    p = "immutable";
-                else
-                    p = "inout";
-                error("cannot remove key from %s associative array %s", p, e->toChars());
+            {   OutBuffer buf;
+                MODtoBuffer(&buf, e->type->mod);
+                error("cannot remove key from %s associative array %s", buf.toChars(), e->toChars());
                 return new ErrorExp();
             }
             Expression *key = (*arguments)[0];

src/func.c

@@ -1234,7 +1234,11 @@ void FuncDeclaration::semantic3(Scope *sc)
                              *    as delegating calls to other constructors
                              */
                             if (v->isCtorinit() && !v->type->isMutable() && cd)
-                                error("missing initializer for final field %s", v->toChars());
+                            {
+                                OutBuffer buf;
+                                MODtoBuffer(&buf, v->type->mod);
+                                error("missing initializer for %s field %s", buf.toChars(), v->toChars());
+                            }
                             else if (v->storage_class & STCnodefaultctor)
                                 error("field %s must be initialized in constructor", v->toChars());
                         }

test/fail_compilation/diag8777a.d

@@ -0,0 +1,12 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag8777a.d(3): Error: constructor diag8777a.Foo.this missing initializer for immutable field bar
+---
+*/
+
+#line 1
+class Foo {
+    immutable int[5] bar;
+    this() {}
+}

test/fail_compilation/diag8777b.d

@@ -0,0 +1,12 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag8777b.d(3): Error: constructor diag8777b.Foo.this missing initializer for const field bar
+---
+*/
+
+#line 1
+class Foo {
+    const int[5] bar;
+    this() {}
+}

test/fail_compilation/diag8777c.d

@@ -0,0 +1,13 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag8777c.d(4): Error: cannot modify const expression x
+---
+*/
+
+#line 1
+void test()
+{
+    const int x;
+    x = 1;
+}

test/fail_compilation/diag8777d.d

@@ -0,0 +1,13 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag8777d.d(4): Error: cannot modify immutable expression x
+---
+*/
+
+#line 1
+void test()
+{
+    immutable int x;
+    x = 1;
+}

test/fail_compilation/diag8777e.d

@@ -0,0 +1,14 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag8777e.d(5): Error: cannot remove key from immutable associative array hash
+---
+*/
+
+#line 1
+immutable(int[int]) hash;
+
+void main()
+{
+    hash.remove(1);
+}

test/fail_compilation/diag8777f.d

@@ -0,0 +1,14 @@
+/*
+TEST_OUTPUT:
+---
+fail_compilation/diag8777f.d(5): Error: cannot remove key from const associative array hash
+---
+*/
+
+#line 1
+const(int[int]) hash;
+
+void main()
+{
+    hash.remove(1);
+}