Put a space in contract expressions

Fixes #448.

src/dfmt/formatter.d

@@ -1135,7 +1135,7 @@ private:
             else if (peekBackIsKeyword)
                 write(" ");
             writeToken();
-            if (!currentIs(tok!"(") && !currentIs(tok!"{") && !currentIs(tok!"comment"))
+            if (!currentIs(tok!"{") && !currentIs(tok!"comment"))
                 write(" ");
             break;
         case tok!"try":
@@ -1169,7 +1169,7 @@ private:
                     current.index);
             if (isFunctionLit && config.dfmt_brace_style == BraceStyle.allman)
                 newline();
-            else if (!isContract)
+            else if (!isContract || currentIs(tok!"("))
                 write(" ");
             break;
         case tok!"is":
@@ -1218,6 +1218,11 @@ private:
                 }
             }
             goto default;
+        case tok!"invariant":
+            writeToken();
+            if (currentIs(tok!"("))
+                write(" ");
+            break;
         default:
             if (peekBackIs(tok!"identifier"))
                 write(" ");

tests/allman/issue0448.d.ref

@@ -0,0 +1,4 @@
+struct S
+{
+    invariant (true);
+}

tests/issue0448.d

@@ -0,0 +1,4 @@
+struct S
+{
+    invariant(true);
+}

tests/otbs/issue0448.d.ref

@@ -0,0 +1,3 @@
+struct S {
+    invariant (true);
+}