Merge pull request #4701 from mbaulch/fix4675

pickBestCandidate: pre-calculate candidates when symbol table modified

tests/overload/importA.nim

@@ -0,0 +1,5 @@
+type
+  Field* = object
+    elemSize*: int
+
+template `+`*(x: untyped, y: Field): untyped = x

tests/overload/importB.nim

@@ -0,0 +1,15 @@
+type
+  Foo*[T] = object
+    v*: T
+
+template `+`*(x: Foo, y: Foo): untyped = x
+
+template newvar*(r: untyped): untyped {.dirty.} =
+  var r: float
+
+template t1*(x: Foo): untyped =
+  newvar(y1)
+  x
+template t2*(x: Foo): untyped =
+  newvar(y2)
+  x

tests/overload/timport.nim

@@ -0,0 +1,7 @@
+# issue 4675
+import importA  # comment this out to make it work
+import importB
+
+var x: Foo[float]
+var y: Foo[float]
+let r = t1(x) + t2(y)