decode unknown dynamic blocks to ensure they are valid

ext/dynblock/expand_body.go

@@ -201,28 +201,14 @@ func (b *expandBody) expandBlocks(schema *hcl.BodySchema, rawBlocks hcl.Blocks,
 					}
 				}
 			} else {
-				// If our top-level iteration value isn't known then we're forced
-				// to compromise since HCL doesn't have any concept of an
-				// "unknown block". In this case then, we'll produce a single
-				// dynamic block with the iterator values set to DynamicVal,
-				// which at least makes the potential for a block visible
-				// in our result, even though it's not represented in a fully-accurate
-				// way.
+				// If our top-level iteration value isn't known then we
+				// substitute an unknownBody, which will cause the entire block
+				// to evaluate to an unknown value.
 				i := b.iteration.MakeChild(spec.iteratorName, cty.DynamicVal, cty.DynamicVal)
 				block, blockDiags := spec.newBlock(i, b.forEachCtx)
 				diags = append(diags, blockDiags...)
 				if block != nil {
-					block.Body = b.expandChild(block.Body, i)
-
-					// We additionally force all of the leaf attribute values
-					// in the result to be unknown so the calling application
-					// can, if necessary, use that as a heuristic to detect
-					// when a single nested block might be standing in for
-					// multiple blocks yet to be expanded. This retains the
-					// structure of the generated body but forces all of its
-					// leaf attribute values to be unknown.
-					block.Body = unknownBody{block.Body}
-
+					block.Body = unknownBody{b.expandChild(block.Body, i)}
 					blocks = append(blocks, block)
 				}
 			}

ext/dynblock/expand_body_test.go

@@ -1,6 +1,7 @@
 package dynblock
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/hashicorp/hcl/v2"
@@ -441,6 +442,28 @@ func TestExpandUnknownBodies(t *testing.T) {
 					},
 				}),
 			},
+			{
+				Type:        "dynamic",
+				Labels:      []string{"invalid_list"},
+				LabelRanges: []hcl.Range{hcl.Range{}},
+				Body: hcltest.MockBody(&hcl.BodyContent{
+					Attributes: hcltest.MockAttrs(map[string]hcl.Expression{
+						"for_each": hcltest.MockExprLiteral(cty.UnknownVal(cty.Map(cty.String))),
+					}),
+					Blocks: hcl.Blocks{
+						{
+							Type: "content",
+							Body: hcltest.MockBody(&hcl.BodyContent{
+								Attributes: hcltest.MockAttrs(map[string]hcl.Expression{
+									"val": hcltest.MockExprTraversalSrc("each.value"),
+									// unexpected attributes should still produce an error
+									"invalid": hcltest.MockExprLiteral(cty.StringVal("static")),
+								}),
+							}),
+						},
+					},
+				}),
+			},
 		},
 	}
 
@@ -574,4 +597,27 @@ func TestExpandUnknownBodies(t *testing.T) {
 		}
 	})
 
+	t.Run("DecodeInvalidList", func(t *testing.T) {
+		decSpec := &hcldec.BlockListSpec{
+			TypeName: "invalid_list",
+			Nested: &hcldec.ObjectSpec{
+				"val": &hcldec.AttrSpec{
+					Name: "val",
+					Type: cty.String,
+				},
+			},
+		}
+
+		_, _, diags := hcldec.PartialDecode(dynBody, decSpec, nil)
+		if len(diags) != 1 {
+			t.Error("expected 1 extraneous argument")
+		}
+
+		want := `Mock body has extraneous argument "invalid"`
+
+		if !strings.Contains(diags.Error(), want) {
+			t.Errorf("unexpected diagnostics: %v", diags)
+		}
+	})
+
 }

hcldec/spec.go

@@ -468,6 +468,9 @@ func (s *BlockListSpec) decode(content *hcl.BodyContent, blockLabels []blockLabe
 			continue
 		}
 
+		val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
+		diags = append(diags, childDiags...)
+
 		if u, ok := childBlock.Body.(UnknownBody); ok {
 			if u.Unknown() {
 				// If any block Body is unknown, then the entire block value
@@ -476,8 +479,6 @@ func (s *BlockListSpec) decode(content *hcl.BodyContent, blockLabels []blockLabe
 			}
 		}
 
-		val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
-		diags = append(diags, childDiags...)
 		elems = append(elems, val)
 		sourceRanges = append(sourceRanges, sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested))
 	}
@@ -629,6 +630,9 @@ func (s *BlockTupleSpec) decode(content *hcl.BodyContent, blockLabels []blockLab
 			continue
 		}
 
+		val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
+		diags = append(diags, childDiags...)
+
 		if u, ok := childBlock.Body.(UnknownBody); ok {
 			if u.Unknown() {
 				// If any block Body is unknown, then the entire block value
@@ -637,8 +641,6 @@ func (s *BlockTupleSpec) decode(content *hcl.BodyContent, blockLabels []blockLab
 			}
 		}
 
-		val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
-		diags = append(diags, childDiags...)
 		elems = append(elems, val)
 		sourceRanges = append(sourceRanges, sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested))
 	}
@@ -751,6 +753,9 @@ func (s *BlockSetSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel
 			continue
 		}
 
+		val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
+		diags = append(diags, childDiags...)
+
 		if u, ok := childBlock.Body.(UnknownBody); ok {
 			if u.Unknown() {
 				// If any block Body is unknown, then the entire block value
@@ -759,8 +764,6 @@ func (s *BlockSetSpec) decode(content *hcl.BodyContent, blockLabels []blockLabel
 			}
 		}
 
-		val, _, childDiags := decode(childBlock.Body, labelsForBlock(childBlock), ctx, s.Nested, false)
-		diags = append(diags, childDiags...)
 		elems = append(elems, val)
 		sourceRanges = append(sourceRanges, sourceRange(childBlock.Body, labelsForBlock(childBlock), s.Nested))
 	}