fix Issue 2091 - D2 final cannot be applied to variable

D2 has `const` ro represent readonly data, therefore the error and suggestion
"perhaps you meant const?" is normally legitimate.
But, if the `final` attribute comes from a label or block style syntax, it's too
restrict against class member layout.

To lift the limitation, display the error only when `final` is *directly* applied on a variable.
Use same method to `synchrionized`, `abstract`, and `override`.

src/declaration.c

@@ -26,6 +26,7 @@
 #include "statement.h"
 #include "ctfe.h"
 #include "target.h"
+#include "hdrgen.h"
 
 /************************************
  * Check to see the aggregate type is nested and its context pointer is
@@ -800,9 +801,10 @@ void VarDeclaration::semantic(Scope *sc)
         scope = NULL;
     }
 
-    /* Pick up storage classes from context, but skip synchronized
+    /* Pick up storage classes from context, but except synchronized,
+     * override, abstract, and final.
      */
-    storage_class |= (sc->stc & ~STCsynchronized);
+    storage_class |= (sc->stc & ~(STCsynchronized | STCoverride | STCabstract | STCfinal));
     if (storage_class & STCextern && init)
         error("extern symbols cannot have initializers");
 
@@ -1107,24 +1109,17 @@ void VarDeclaration::semantic(Scope *sc)
     else if (type->isWild())
         storage_class |= STCwild;
 
-    if (storage_class & (STCmanifest | STCstatic | STCgshared))
+    if (StorageClass stc = storage_class & (STCsynchronized | STCoverride | STCabstract | STCfinal))
     {
-    }
-    else if (isSynchronized())
-    {
-        error("variable %s cannot be synchronized", toChars());
-    }
-    else if (isOverride())
-    {
-        error("override cannot be applied to variable");
-    }
-    else if (isAbstract())
-    {
-        error("abstract cannot be applied to variable");
-    }
-    else if (storage_class & STCfinal)
-    {
-        error("final cannot be applied to variable, perhaps you meant const?");
+        if (stc == STCfinal)
+            error("cannot be final, perhaps you meant const?");
+        else
+        {
+            OutBuffer buf;
+            stcToBuffer(&buf, stc);
+            error("cannot be %s", buf.peekString());
+        }
+        storage_class &= ~stc;  // strip off
     }
 
     if (storage_class & (STCstatic | STCextern | STCmanifest | STCtemplateparameter | STCtls | STCgshared | STCctfe))

test/fail_compilation/fail170.d

@@ -1,7 +1,7 @@
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/fail170.d(8): Error: variable fail170.foo.x final cannot be applied to variable, perhaps you meant const?
+fail_compilation/fail170.d(8): Error: variable fail170.foo.x cannot be final, perhaps you meant const?
 ---
 */
 

test/fail_compilation/fail179.d

@@ -1,7 +1,7 @@
 /*
 TEST_OUTPUT:
 ---
-fail_compilation/fail179.d(11): Error: variable fail179.main.px final cannot be applied to variable, perhaps you meant const?
+fail_compilation/fail179.d(11): Error: variable fail179.main.px cannot be final, perhaps you meant const?
 ---
 */
 

test/fail_compilation/fail180.d

@@ -5,8 +5,8 @@ fail_compilation/fail180.d(23): Error: cannot modify const expression this.x
 fail_compilation/fail180.d(24): Error: cannot modify const expression this.x
 fail_compilation/fail180.d(38): Error: cannot modify const expression this.x
 fail_compilation/fail180.d(39): Error: cannot modify const expression this.x
-fail_compilation/fail180.d(50): Error: variable fail180.main.t final cannot be applied to variable, perhaps you meant const?
-fail_compilation/fail180.d(62): Error: variable fail180.test.d final cannot be applied to variable, perhaps you meant const?
+fail_compilation/fail180.d(50): Error: variable fail180.main.t cannot be final, perhaps you meant const?
+fail_compilation/fail180.d(62): Error: variable fail180.test.d cannot be final, perhaps you meant const?
 ---
 */
 

test/fail_compilation/failattr.d

@@ -0,0 +1,34 @@
+// REQUIRED_ARGS: -o-
+
+/*
+TEST_OUTPUT:
+---
+fail_compilation/failattr.d(16): Error: variable failattr.C2901.v1 cannot be synchronized
+fail_compilation/failattr.d(17): Error: variable failattr.C2901.v2 cannot be override
+fail_compilation/failattr.d(18): Error: variable failattr.C2901.v3 cannot be abstract
+fail_compilation/failattr.d(19): Error: variable failattr.C2901.v4 cannot be final, perhaps you meant const?
+fail_compilation/failattr.d(31): Error: variable failattr.C2901.v13 cannot be final abstract synchronized override
+fail_compilation/failattr.d(33): Error: variable failattr.C2901.v14 cannot be final, perhaps you meant const?
+---
+*/
+class C2901
+{
+    synchronized    int v1;         // error
+    override        int v2;         // error
+    abstract        int v3;         // error
+    final           int v4;         // error
+
+    synchronized    { int v5; }     // no error
+    override        { int v6; }     // no error
+    abstract        { int v7; }     // no error
+    final           { int v8; }     // no error
+
+    synchronized:   int v9;         // no error
+    override:       int v10;        // no error
+    abstract:       int v11;        // no error
+    final:          int v12;        // no error
+
+    synchronized override abstract final int v13;   // one line error
+
+    static final int v14;           // error, even if static is applied at the same time
+}