BUG: fractionExpr "0" ignored (fixes #1855)

- incorrect branching logic caused the "0" case to be ignored

src/finiteVolume/expressions/fields/base/patchExprFieldBase.C

@@ -5,8 +5,8 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Original code Copyright (C) 2011-2018 Bernhard Gschaider
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2011-2018 Bernhard Gschaider
+    Copyright (C) 2019-2020 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -31,6 +31,7 @@ License
 #include "fvMesh.H"
 #include "fvPatch.H"
 #include "pointMesh.H"
+#include "stringOps.H"
 
 // * * * * * * * * * * * * * Static Member Functions * * * * * * * * * * * * //
 
@@ -118,7 +119,6 @@ Foam::expressions::patchExprFieldBase::patchExprFieldBase
         else
         {
             // No gradient expression - same as Zero
-
             if (debug_)
             {
                 Info<< "No gradientExpr" << nl;
@@ -127,7 +127,14 @@ Foam::expressions::patchExprFieldBase::patchExprFieldBase
 
         if (dict.readIfPresent("fractionExpr", expr))
         {
-            if (!expr.empty() && expr != "0")
+            stringOps::inplaceTrim(expr);
+
+            if (expr == "0" || expr == "1")
+            {
+                // Special cases, handled with more efficiency
+                fracExpr_ = expr;
+            }
+            else if (!expr.empty())
             {
                 if (isPointVal)
                 {
@@ -137,12 +144,10 @@ Foam::expressions::patchExprFieldBase::patchExprFieldBase
                 fracExpr_ = expressions::exprString(expr, dict);
             }
         }
-        else
-        {
-            // No fraction expression - same as 1 (one)
+
+        // No fraction expression? - defer treatment to inherited BC
         // Mixed BC may elect to simply ignore gradient expression
     }
-    }
 }