`strip_string_quotes=True` returns `$${` and `%%{` unresolved, so the value differs from Terraform's

[livingstaccato]

Summary

HCL's two template escapes, $${ and %%{, mean a literal ${ and %{.
strip_string_quotes=True asks for a string's value rather than its source,
and resolves \n, \r, \t, \", \\ and the unicode escapes -- but not
these two. The value therefore keeps a doubled sigil that Terraform does not.

Reproduction

import hcl2
from hcl2.utils import SerializationOptions

value = SerializationOptions(preserve_heredocs=False, strip_string_quotes=True)

hcl2.loads('a = <<EOT\n$${esc}\nEOT\n', serialization_options=value)["a"]  # '$${esc}'
hcl2.loads('a = <<EOT\n%%{d}\nEOT\n',  serialization_options=value)["a"]  # '%%{d}'
hcl2.loads('a = "$${esc}"\n',          serialization_options=value)["a"]  # '$${esc}'

OpenTofu evaluates the same three to "${esc}\n", "%{d}\n" and "${esc}".

Both string forms are affected, so the fix is not heredoc-specific: the quoted
form goes through StringRule.serialize (hcl2/rules/strings.py:115 at
v8.1.3, resolving escapes via _serialize_part_as_value at :133), the
heredoc form through HeredocTemplateRule.serialize (:164). Neither
consults the two template escapes; hcl2/utils.py:50 _SIMPLE_ESCAPES lists
the five backslash forms it does resolve.

Suggested shape of the fix

Resolve the two sequences wherever the value form is produced. $$ not
followed by { is literal in both implementations, and so is %% -- the rule
is exactly $${ and %%{, not the doubled sigil on its own.

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This issue, and the investigation behind it, were produced by an AI assistant (Claude) working on behalf of the author. Please review with that provenance in mind.