hcldec: Handle or forbid cty.DynamicPseudoType attributes in nested blocks

Our BlockList, BlockSet, and BlockMap specs all produce cty collection
values, which require all elements to have a homogeneous type. If the
nested spec contained an attribute of type cty.DynamicPseudoType, that
would create the risk of each element having a different type, which would
previously have caused decoding to panic.

Now we either handle this during decode (BlockList, BlockSet) or forbid
it outright (BlockMap) to prevent that crash. BlockMap could _potentially_
also handle this during decode, but that would require a more significant
reorganization of its implementation than I want to take on right now,
and decoding dynamically-typed values inside collections is an edge case
anyway.

1 files changed, 9 insertions, 0 deletions

diff --git a/cmd/hcldec/spec.go b/cmd/hcldec/spec.go
index b62f05b..c8b90d3 100644
--- a/cmd/hcldec/spec.go
+++ b/cmd/hcldec/spec.go
@@ -394,6 +394,15 @@ func decodeBlockMapSpec(body hcl.Body, impliedName string) (hcldec.Spec, hcl.Dia
 		return errSpec, diags
 	}
 
+	if hcldec.ImpliedType(spec).HasDynamicTypes() {
+		diags = append(diags, &hcl.Diagnostic{
+			Severity: hcl.DiagError,
+			Summary:  "Invalid block_map spec",
+			Detail:   "A block_map spec may not contain attributes with type 'any'.",
+			Subject:  body.MissingItemRange().Ptr(),
+		})
+	}
+
 	return spec, diags
 }