command/format: Fix rendering of different types

command/format/diff.go

@@ -556,6 +556,7 @@ func (p *blockBodyDiffPrinter) writeValue(val cty.Value, action plans.Action, in
 
 func (p *blockBodyDiffPrinter) writeValueDiff(old, new cty.Value, indent int, path cty.Path) {
 	ty := old.Type()
+	typesEqual := ctyTypesEqual(ty, new.Type())
 
 	// We have some specialized diff implementations for certain complex
 	// values where it's useful to see a visualization of the diff of
@@ -563,7 +564,7 @@ func (p *blockBodyDiffPrinter) writeValueDiff(old, new cty.Value, indent int, pa
 	// new values verbatim.
 	// However, these specialized implementations can apply only if both
 	// values are known and non-null.
-	if old.IsKnown() && new.IsKnown() && !old.IsNull() && !new.IsNull() {
+	if old.IsKnown() && new.IsKnown() && !old.IsNull() && !new.IsNull() && typesEqual {
 		switch {
 		case ty == cty.String:
 			// We have special behavior for both multi-line strings in general
@@ -1060,6 +1061,19 @@ func ctyEqualWithUnknown(old, new cty.Value) bool {
 	return old.Equals(new).True()
 }
 
+// ctyTypesEqual checks equality of two types more loosely
+// by avoiding checks of object/tuple elements
+// as we render differences on element-by-element basis anyway
+func ctyTypesEqual(oldT, newT cty.Type) bool {
+	if oldT.IsObjectType() && newT.IsObjectType() {
+		return true
+	}
+	if oldT.IsTupleType() && newT.IsTupleType() {
+		return true
+	}
+	return oldT.Equals(newT)
+}
+
 func ctyEnsurePathCapacity(path cty.Path, minExtra int) cty.Path {
 	if cap(path)-len(path) >= minExtra {
 		return path

command/format/diff_test.go

@@ -286,7 +286,7 @@ func TestResourceChange_JSON(t *testing.T) {
     }
 `,
 		},
-		"in-place update": {
+		"in-place update of object": {
 			Action: plans.Update,
 			Mode:   addrs.ManagedResourceMode,
 			Before: cty.ObjectVal(map[string]cty.Value{
@@ -763,6 +763,45 @@ func TestResourceChange_JSON(t *testing.T) {
             }
         )
     }
+`,
+		},
+		"in-place update from object to tuple": {
+			Action: plans.Update,
+			Mode:   addrs.ManagedResourceMode,
+			Before: cty.ObjectVal(map[string]cty.Value{
+				"id":         cty.StringVal("i-02ae66f368e8518a9"),
+				"json_field": cty.StringVal(`{"aaa": [42, {"foo":"bar"}, "value"]}`),
+			}),
+			After: cty.ObjectVal(map[string]cty.Value{
+				"id":         cty.UnknownVal(cty.String),
+				"json_field": cty.StringVal(`["aaa", 42, "something"]`),
+			}),
+			Schema: &configschema.Block{
+				Attributes: map[string]*configschema.Attribute{
+					"id":         {Type: cty.String, Optional: true, Computed: true},
+					"json_field": {Type: cty.String, Optional: true},
+				},
+			},
+			RequiredReplace: cty.NewPathSet(),
+			ExpectedOutput: `  # test_instance.example will be updated in-place
+  ~ resource "test_instance" "example" {
+      ~ id         = "i-02ae66f368e8518a9" -> (known after apply)
+      ~ json_field = jsonencode(
+          ~ {
+              - aaa = [
+                  - 42,
+                  - {
+                      - foo = "bar"
+                    },
+                  - "value",
+                ]
+            } -> [
+              + "aaa",
+              + 42,
+              + "something",
+            ]
+        )
+    }
 `,
 		},
 	}