This PR supports N levels of nested embedded struct types and applies the sametfsdk tag restrictions/validations regardless of where the tag appears in the struct.

Example

typethingResourceModelstruct {Attr1 types.String`tfsdk:"attr_1"`Attr2 types.Bool`tfsdk:"attr_2"`CommonModel}typeCommonModelstruct {Attr3 types.Int64`tfsdk:"attr_3"`Attr4 types.List`tfsdk:"attr_4"`EvenMoreCommonModel}typeEvenMoreCommonModelstruct {Attr5 types.String`tfsdk:"attr_5"`Attr6 types.Map`tfsdk:"attr_6"`}func (r*thingResource)Schema(ctx context.Context,req resource.SchemaRequest,resp*resource.SchemaResponse) {resp.Schema= schema.Schema{Attributes:map[string]schema.Attribute{"attr_1": schema.StringAttribute{Required:true,            },"attr_2": schema.BoolAttribute{Computed:true,PlanModifiers: []planmodifier.Bool{boolplanmodifier.UseStateForUnknown(),                },            },"attr_3": schema.Int64Attribute{Required:true,            },"attr_4": schema.ListAttribute{ElementType:types.StringType,Computed:true,PlanModifiers: []planmodifier.List{listplanmodifier.UseStateForUnknown(),                },            },"attr_5": schema.StringAttribute{Required:true,            },"attr_6": schema.MapAttribute{ElementType:types.BoolType,Computed:true,PlanModifiers: []planmodifier.Map{mapplanmodifier.UseStateForUnknown(),                },            },        },    }}

The same example schema could also be represented by these model combinations:

typethingResourceModelstruct {Attr1 types.String`tfsdk:"attr_1"`Attr2 types.Bool`tfsdk:"attr_2"`CommonModelEvenMoreCommonModel}typeCommonModelstruct {Attr3 types.Int64`tfsdk:"attr_3"`Attr4 types.List`tfsdk:"attr_4"`}typeEvenMoreCommonModelstruct {Attr5 types.String`tfsdk:"attr_5"`Attr6 types.Map`tfsdk:"attr_6"`}

Notes

Additional test coverage:Add reflection tests for object models withtfsdk tags in framework providers terraform-provider-corner#263
To avoid having to refactor a good chunk of our reflection logic, we explicitly are not supporting struct embedding with pointers. That doesn't stop us from adding support in the future if it's deemed necessary (although supporting unexported struct embeds from pointers I don't think we can do)
- Theencoding/json library supports exported struct embedding via pointers, but it was also historically relying on a bug in Go that allowed setting unexported struct embedding with pointers to work. When that bug was fixed, they chose not to completely remove pointer struct embedding for compatibility reasons.
This PR could be considered a change in behavior, as it adds support for unexported embedded structs which promote exported fields
- These would be previously ignored, but now could potentially raise an error diagnostic iftfsdk ignore tags are not included

typethingResourceModelstruct {Attr1 types.String`tfsdk:"attr_1"`Attr2 types.Bool`tfsdk:"attr_2"`existingModel}typeexistingModelstruct {FieldNotRelatedstring// Needs a tfsdk tag now!}

You can ignore an entire embedded struct via the typical ignore tag

typethingResourceModelstruct {Attr1 types.String`tfsdk:"attr_1"`Attr2 types.Bool`tfsdk:"attr_2"`existingModel`tfsdk:"-"`// Ignored!}typeexistingModelstruct {FieldNotRelatedstring}