Commits on May 5, 2016

1. helper/schema: Normalize bools to "true"/"false" in diffs …

   For a long time now, the diff logic has relied on the behavior of
   `mapstructure.WeakDecode` to determine how various primitives are
   converted into strings.  The `schema.DiffString` function is used for
   all primitive field types: TypeBool, TypeInt, TypeFloat, and TypeString.
   
   The `mapstructure` library's string representation of booleans is "0"
   and "1", which differs from `strconv.FormatBool`'s "false" and "true"
   (which is used in writing out boolean fields to the state).
   
   Because of this difference, diffs have long had the potential for
   cosmetically odd but semantically neutral output like:
   
       "true" => "1"
       "false" => "0"
   
   So long as `mapstructure.Decode` or `strconv.ParseBool` are used to
   interpret these strings, there's no functional problem.
   
   We had our first clear functional problem with #6005 and friends, where
   users noticed diffs like the above showing up unexpectedly and causing
   troubles when `ignore_changes` was in play.
   
   This particular bug occurs down in Terraform core's EvalIgnoreChanges.
   There, the diff is modified to account for ignored attributes, and
   special logic attempts to handle properly the situation where the
   ignored attribute was going to trigger a resource replacement. That
   logic relies on the string representations of the Old and New fields in
   the diff to be the same so that it filters properly.
   
   So therefore, we now get a bug when a diff includes `Old: "0", New:
   "false"` since the strings do not match, and `ignore_changes` is not
   properly handled.
   
   Here, we introduce `TypeBool`-specific normalizing into `finalizeDiff`.
   I spiked out a full `diffBool` function, but figuring out which pieces
   of `diffString` to duplicate there got hairy. This seemed like a simpler
   and more direct solution.
   
   Fixes #6005 (and potentially others!)

   

   phinze committed May 5, 2016
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