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terraform: Stabilize the variable_validation_crossref experiment #34955

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terraform: Stabilize the variable_validation_crossref experiment #34955

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Commits on Apr 5, 2024

  1. terraform: lang.Data fake for use in unit tests 

    Our real implementation of the lang.Data interface depends on just about
everything else in the modules runtime to implement its behavior, and so
it's not really appropriate to use in unit tests.

This new implementation is considerably simpler, just returning values
predefined in a set of fixed tables. This is appropriate for unit tests of
features that perform expression evaluation as a side-effect of their work
but that don't contribute their own values to the real evaluation data
implementation.
    @apparentlymart
    apparentlymart committed Apr 5, 2024
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  2. terraform: Stabilize the variable_validation_crossref experiment 

    Previously we introduced a language experiment that would permit variable
validation rules to refer to other objects declared in the same module
as the variable.

Now that experiment is concluded and its behavior is available for all
modules.

This final version deviates slightly from the experiment: we learned from
the experimental implementation that we accidentally made the "validate"
command able to validate constant-valued input variables in child modules
despite the usual rule that input variables are unknown during validation,
because the previous compromise bypassed the main expression evaluator
and built its own evaluation context directly.

Even though that behavior was not intended, it's a useful behavior that is
protected by our compatibility promises and so this commit includes a
slightly hacky emulation of that behavior, in eval_variable.go, that
fetches the variable value in the same way the old implementation would
have and then modifies the hcl evaluation context to include that value,
while preserving anything else that our standard evaluation context
builder put in there. That narrowly preserves the old behavior for
expressions that compare the variable value directly to a constant, while
treating all other references (which were previously totally invalid) in
the standard way. This quirk was already covered by the existing test
TestContext2Validate_variableCustomValidationsFail, which fails if the
special workaround is removed.
    @apparentlymart
    apparentlymart committed Apr 5, 2024
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