unknown upgraded splat values may have no elems

When upgrading an unknown splat value, the resulting collection may have
0 elements if the value ends up being `null`. This means the type must
be dynamic.

hclsyntax/expression.go

@@ -1439,10 +1439,10 @@ func (e *SplatExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
  // upgrade to a different number of elements depending on whether
  // sourceVal becomes null or not.
  // We record this condition here so we can process any remaining
- // expression after the * to derive the correct type. For example, it
- // is valid to use a splat on a single object to retrieve a list of a
- // single attribute, which means the final expression type still needs
- // to be determined.
+ // expression after the * to verify the result of the traversal. For
+ // example, it is valid to use a splat on a single object to retrieve a
+ // list of a single attribute, but we still need to check if that
+ // attribute actually exists.
  upgradedUnknown = !sourceVal.IsKnown()
 
  sourceVal = cty.TupleVal([]cty.Value{sourceVal})
@@ -1512,7 +1512,11 @@ func (e *SplatExpr) Value(ctx *hcl.EvalContext) (cty.Value, hcl.Diagnostics) {
  }
  e.Item.clearValue(ctx) // clean up our temporary value
 
- if !isKnown || upgradedUnknown {
+ if upgradedUnknown {
+ return cty.DynamicVal, diags
+ }
+
+ if !isKnown {
  // We'll ingore the resultTy diagnostics in this case since they
  // will just be the same errors we saw while iterating above.
  ty, _ := resultTy()

hclsyntax/expression_test.go

@@ -1142,7 +1142,7 @@ upper(
  "unkstr": cty.UnknownVal(cty.String),
  },
  },
- cty.UnknownVal(cty.Tuple([]cty.Type{cty.String})),
+ cty.DynamicVal,
  0,
  },
  {
@@ -1152,7 +1152,7 @@ upper(
  "unkstr": cty.UnknownVal(cty.String),
  },
  },
- cty.UnknownVal(cty.Tuple([]cty.Type{cty.DynamicPseudoType})),
+ cty.DynamicVal,
  1, // a string has no attribute "name"
  },
  {
@@ -1174,7 +1174,19 @@ upper(
  })),
  },
  },
- cty.UnknownVal(cty.Tuple([]cty.Type{cty.String})),
+ cty.DynamicVal,
+ 0,
+ },
+ {
+ `unkobj.*.names`,
+ &hcl.EvalContext{
+ Variables: map[string]cty.Value{
+ "unkobj": cty.UnknownVal(cty.Object(map[string]cty.Type{
+ "names": cty.List(cty.String),
+ })),
+ },
+ },
+ cty.DynamicVal,
  0,
  },
  {