set length is unknown with partially known elems

If a set contains partially known values the length is unknown which
causes assertPlannedObjectValid to fail valid plans.

Revert to the old method if using LengthInt for the set lengths, which
returns the maximum number of possible elements, with a guard for
entirely unknown set values.

internal/plans/objchange/plan_valid.go

@@ -342,6 +342,11 @@ func assertPlannedObjectValid(schema *configschema.Object, prior, config, planne
 		errs = append(errs, path.NewErrorf("planned for existence but config wants absence"))
 		return errs
 	}
+	if !config.IsNull() && !planned.IsKnown() {
+		errs = append(errs, path.NewErrorf("planned unknown for configured value"))
+		return errs
+	}
+
 	if planned.IsNull() {
 		// No further checks possible if the planned value is null
 		return errs
@@ -442,16 +447,14 @@ func assertPlannedObjectValid(schema *configschema.Object, prior, config, planne
 		}
 
 	case configschema.NestingSet:
-		plannedL := planned.Length()
-		configL := config.Length()
-
-		// config wasn't known, then planned should be unknown too
-		if !plannedL.IsKnown() && !configL.IsKnown() {
+		if !planned.IsKnown() || !config.IsKnown() {
+			// if either is unknown we cannot check the lengths
 			return errs
 		}
 
-		lenEqual := plannedL.Equals(configL)
-		if !lenEqual.IsKnown() || lenEqual.False() {
+		plannedL := planned.LengthInt()
+		configL := config.LengthInt()
+		if plannedL != configL {
 			errs = append(errs, path.NewErrorf("count in plan (%#v) disagrees with count in config (%#v)", plannedL, configL))
 			return errs
 		}

internal/plans/objchange/plan_valid_test.go

@@ -1700,7 +1700,7 @@ func TestAssertPlanValid(t *testing.T) {
 			&configschema.Block{
 				Attributes: map[string]*configschema.Attribute{
 					"set": {
-						Computed: true,
+						//Computed: true,
 						Optional: true,
 						NestedType: &configschema.Object{
 							Nesting: configschema.NestingSet,
@@ -1796,9 +1796,9 @@ func TestAssertPlanValid(t *testing.T) {
 				)),
 			}),
 			[]string{
-				`.set: count in plan (cty.UnknownVal(cty.Number).Refine().NotNull().NumberLowerBound(cty.NumberIntVal(0), true).NumberUpperBound(cty.NumberIntVal(9.223372036854775807e+18), true).NewValue()) disagrees with count in config (cty.NumberIntVal(1))`,
-				`.list: count in plan (cty.UnknownVal(cty.Number).Refine().NotNull().NumberLowerBound(cty.NumberIntVal(0), true).NumberUpperBound(cty.NumberIntVal(9.223372036854775807e+18), true).NewValue()) disagrees with count in config (cty.NumberIntVal(1))`,
-				`.map: count in plan (cty.UnknownVal(cty.Number).Refine().NotNull().NumberLowerBound(cty.NumberIntVal(0), true).NumberUpperBound(cty.NumberIntVal(9.223372036854775807e+18), true).NewValue()) disagrees with count in config (cty.NumberIntVal(1))`,
+				`.set: planned unknown for configured value`,
+				`.list: planned unknown for configured value`,
+				`.map: planned unknown for configured value`,
 			},
 		},
 
@@ -1829,6 +1829,68 @@ func TestAssertPlanValid(t *testing.T) {
 			}),
 			nil,
 		},
+
+		"nested set values can contain computed unknown": {
+			&configschema.Block{
+				Attributes: map[string]*configschema.Attribute{
+					"set": {
+						Optional: true,
+						NestedType: &configschema.Object{
+							Nesting: configschema.NestingSet,
+							Attributes: map[string]*configschema.Attribute{
+								"input": {
+									Type:     cty.String,
+									Optional: true,
+								},
+								"computed": {
+									Type:     cty.String,
+									Computed: true,
+									Optional: true,
+								},
+							},
+						},
+					},
+				},
+			},
+			cty.ObjectVal(map[string]cty.Value{
+				"set": cty.SetVal([]cty.Value{
+					cty.ObjectVal(map[string]cty.Value{
+						"input":    cty.StringVal("a"),
+						"computed": cty.NullVal(cty.String),
+					}),
+					cty.ObjectVal(map[string]cty.Value{
+						"input":    cty.StringVal("b"),
+						"computed": cty.NullVal(cty.String),
+					}),
+				}),
+			}),
+			cty.ObjectVal(map[string]cty.Value{
+				"set": cty.SetVal([]cty.Value{
+					cty.ObjectVal(map[string]cty.Value{
+						"input":    cty.StringVal("a"),
+						"computed": cty.NullVal(cty.String),
+					}),
+					cty.ObjectVal(map[string]cty.Value{
+						"input":    cty.StringVal("b"),
+						"computed": cty.NullVal(cty.String),
+					}),
+				}),
+			}),
+			// Plan can mark the null computed values as unknown
+			cty.ObjectVal(map[string]cty.Value{
+				"set": cty.SetVal([]cty.Value{
+					cty.ObjectVal(map[string]cty.Value{
+						"input":    cty.StringVal("a"),
+						"computed": cty.UnknownVal(cty.String),
+					}),
+					cty.ObjectVal(map[string]cty.Value{
+						"input":    cty.StringVal("b"),
+						"computed": cty.UnknownVal(cty.String),
+					}),
+				}),
+			}),
+			[]string{},
+		},
 	}
 
 	for name, test := range tests {