improvements for idetools; system.compiles improved

compiler/semdata.nim

@@ -78,11 +78,41 @@ type
 var
   gGenericsCache: PGenericsCache # save for modularity
 
-proc newGenericsCache: PGenericsCache =
+proc newGenericsCache*(): PGenericsCache =
   new(result)
   initIdTable(result.InstTypes)
   result.generics = @[]
 
+proc tempContext*(c: PContext): PContext =
+  ## generates a temporary context so that side-effects can be rolled-back;
+  ## necessary for ``system.compiles``.
+  new(result)
+  result.module = c.module
+  result.p = c.p
+  # don't use the old cache:
+  result.generics = newGenericsCache()
+  result.friendModule = c.friendModule
+  result.InstCounter = c.InstCounter
+  result.threadEntries = @[]
+  # hrm, 'tab' is expensive to copy ... so we don't. We open a new scope
+  # instead to be able to undo scope changes. Not entirely correct for
+  # explicit 'global' vars though:
+  #shallowCopy(result.tab, c.tab)
+  assign(result.AmbiguousSymbols, c.AmbiguousSymbols)
+  result.InGenericContext = c.InGenericContext
+  result.InUnrolledContext = c.InUnrolledContext
+  result.InCompilesContext = c.InCompilesContext
+  result.converters = c.converters
+  result.semConstExpr = c.semConstExpr
+  result.semExpr = c.semExpr
+  result.semConstBoolExpr = c.semConstBoolExpr
+  assign(result.includedFiles, c.includedFiles) 
+  result.filename = c.filename
+  #shallowCopy(result.userPragmas, c.userPragmas) 
+  # XXX mark it as read-only:
+  result.evalContext = c.evalContext
+  
+
 proc newContext*(module: PSym, nimfile: string): PContext
 
 proc lastOptionEntry*(c: PContext): POptionEntry