Avoid concatenating lists of one string

src/libexpr/eval.cc

@@ -965,7 +965,7 @@ void ExprConcatStrings::eval(EvalState & state, Env & env, Value & v)
             isPath = vStr.type == tPath;
             first = false;
         }
-            
+
         s << state.coerceToString(vStr, context, false, !isPath);
     }
         

src/libexpr/parser.y

@@ -203,7 +203,7 @@ static Expr * stripIndentation(SymbolTable & symbols, vector<Expr *> & es)
         es2->push_back(new ExprString(symbols.create(s2)));
     }
 
-    return new ExprConcatStrings(es2);
+    return es2->size() == 1 ? (*es2)[0] : new ExprConcatStrings(es2);
 }