Avoid multiple potential full-AOT failures with LINQ Enumerable. Fix bug #3285

diff --git a/mcs/class/System.Core/System.Linq/Enumerable.cs b/mcs/class/System.Core/System.Linq/Enumerable.cs
index 0dcdb6d8191a9d474e40e30fa5f066376027f933..397b3301ed12996f1b9badf902d2b6c9ef755296 100644 (file)
--- a/mcs/class/System.Core/System.Linq/Enumerable.cs
+++ b/mcs/class/System.Core/System.Linq/Enumerable.cs
@@ -854,7 +854,11 @@ namespace System.Linq
 #if !FULL_AOT_RUNTIME
                        return source.First (PredicateOf<TSource>.Always, Fallback.Default);
 #else
-                       return source.First (delegate { return true; }, Fallback.Default);
+                       // inline the code to reduce dependency o generic causing AOT errors on device (e.g. bug #3285)
+                       foreach (var element in source)
+                               return element;
+
+                       return default (TSource);
 #endif
                }
 
@@ -1217,7 +1221,18 @@ namespace System.Linq
 #if !FULL_AOT_RUNTIME
                        return source.Last (PredicateOf<TSource>.Always, Fallback.Throw);
 #else
-                       return source.Last (delegate { return true; }, Fallback.Throw);
+                       var empty = true;
+                       var item = default (TSource);
+
+                       foreach (var element in source) {
+                               item = element;
+                               empty = false;
+                       }
+
+                       if (!empty)
+                               return item;
+
+                       throw new InvalidOperationException ();
 #endif
                }
 
@@ -1243,7 +1258,18 @@ namespace System.Linq
 #if !FULL_AOT_RUNTIME
                        return source.Last (PredicateOf<TSource>.Always, Fallback.Default);
 #else
-                       return source.Last (delegate { return true; }, Fallback.Default);
+                       var empty = true;
+                       var item = default (TSource);
+
+                       foreach (var element in source) {
+                               item = element;
+                               empty = false;
+                       }
+
+                       if (!empty)
+                               return item;
+
+                       return item;
 #endif
                }
 
@@ -2360,7 +2386,21 @@ namespace System.Linq
 #if !FULL_AOT_RUNTIME
                        return source.Single (PredicateOf<TSource>.Always, Fallback.Throw);
 #else
-                       return source.Single (delegate { return true; }, Fallback.Throw);
+                       var found = false;
+                       var item = default (TSource);
+
+                       foreach (var element in source) {
+                               if (found)
+                                       throw new InvalidOperationException ();
+
+                               found = true;
+                               item = element;
+                       }
+
+                       if (!found)
+                               throw new InvalidOperationException ();
+
+                       return item;
 #endif
                }
 
@@ -2382,7 +2422,18 @@ namespace System.Linq
 #if !FULL_AOT_RUNTIME
                        return source.Single (PredicateOf<TSource>.Always, Fallback.Default);
 #else
-                       return source.Single (delegate { return true; }, Fallback.Default);
+                       var found = false;
+                       var item = default (TSource);
+
+                       foreach (var element in source) {
+                               if (found)
+                                       throw new InvalidOperationException ();
+
+                               found = true;
+                               item = element;
+                       }
+
+                       return item;
 #endif
                }