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convert: Fix converting to nested dynamic map #47

Merged
merged 3 commits into from
Mar 3, 2020
Merged

convert: Fix converting to nested dynamic map #47

merged 3 commits into from
Mar 3, 2020

Commits on Mar 3, 2020

  1. convert: Fix converting to nested dynamic map 

    When converting an object tree to a nested dynamic map (for example,
`cty.Map(cty.Map(cty.DynamicPseudoType))` or deeper), it is necessary to
unify the types of the child elements of the map.

Previously, we would only apply this process to the innermost leaf
object's attributes, which could result in local unification but
globally incompatible types. This caused a panic when converting the
single top-level object into a map with concrete type, as the types of
the sub-trees were incompatible.

This commit addresses this class of bugs in two ways: adding type
unification for multi-level map and object structures, and fallback
error handling to prevent panics for this class of failure.

The additional type unification process has several steps:

- First, we add a second unify & convert step at the end of the process,
  immediately before constructing the final map. This second unification
  ensures that not only sibling elements but also cousins are of the
  same type.

- We also ensure that generated type information is preserved for empty
  collections, by returning an empty map of the detected type, instead
  of the dynamic type. This prevents a multi-step unification bouncing
  back and forth between concrete and dynamic element types.

- Finally, we add a specific unification procedure for map-to-map
  conversions. This inspects and unifies the element types for the maps
  which are being converted. For example, a populated map(string) and an
  empty map(any) will be unified to a map(string) type.

Tests are extended to cover reduced configurations from the three source
Terraform bugs which prompted this work.
    @alisdair
    alisdair committed Mar 3, 2020
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  2. Update cty/convert/public_test.go 

    Co-Authored-By: Kristin Laemmert <[email protected]>
    @alisdair @mildwonkey
    alisdair and mildwonkey authored Mar 3, 2020
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  3. Fix potential panic in unreachable code

    @alisdair
    alisdair committed Mar 3, 2020
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