[Breaking] Remove UnknownValue from shim.Schema

[iwahbe]

It looks like nothing uses this code, so we don't need to keep it around. While this is technically a breaking change, I don't expect that anyone would use this method.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.67%. Comparing base (98847bf) to head (ba4194d).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1974      +/-   ##
==========================================
+ Coverage   60.55%   60.67%   +0.11%     
==========================================
  Files         331      331              
  Lines       44726    44648      -78     
==========================================
+ Hits        27084    27090       +6     
+ Misses      16120    16036      -84     
  Partials     1522     1522              

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[t0yv0]

No concerns of this change breaking anyone, but there is some knowledge encoded here that's worth calling out, at the very least in #1904

Similar code to this one has moved (or been copied) to MakeTerraformInputs and is causing problems.

Fundamentally my theory of what this is about is that list/set-nested blocks in TF can never accept null or unknown value but in Pulumi the projection of these blocks does indeed have to handle receiving nulls and unknowns. It appears that it has attempted doing so by replacing them with plausible empty values.

Is this common knowledge or should I take time to document/track a bit more? If this is understood I'm LGTM on merging the simplification.

[iwahbe]

I think that as long as the code is present in MakeTerraformInputs (where it is actually used), then I'm happy with it as is.

Fundamentally my theory of what this is about is that list/set-nested blocks in TF can never accept null or unknown value but in Pulumi the projection of these blocks does indeed have to handle receiving nulls and unknowns. It appears that it has attempted doing so by replacing them with plausible empty values.

This is definitely what the code is supposed to do. The code is just never invoked.

Is this common knowledge or should I take time to document/track a bit more? If this is understood I'm LGTM on merging the simplification.

I don't think it's common knowledge but it is present in the part of the code base where it is needed: MakeTerraformInputs.