core: ResourceAddress.HasResourceSpec method

The resource address documentation defines a resource address as being in
two parts: the module path and the resource spec. The resource spec can
be omitted, which represents addressing _all_ resources in a module.

In some cases (such as import) it doesn't make sense to address an entire
module, so this helper makes it easy for validation code to check for
this to reject insufficiently-specific resource addresses.

terraform/resource_address.go

@@ -89,6 +89,15 @@ func (r *ResourceAddress) String() string {
 	return strings.Join(result, ".")
 }
 
+// HasResourceSpec returns true if the address has a resource spec, as
+// defined in the documentation:
+//    https://www.terraform.io/docs/internals/resource-addressing.html
+// In particular, this returns false if the address contains only
+// a module path, thus addressing the entire module.
+func (r *ResourceAddress) HasResourceSpec() bool {
+	return r.Type != "" && r.Name != ""
+}
+
 // stateId returns the ID that this resource should be entered with
 // in the state. This is also used for diffs. In the future, we'd like to
 // move away from this string field so I don't export this.

terraform/resource_address_test.go

@@ -628,3 +628,60 @@ func TestResourceAddressStateId(t *testing.T) {
 		})
 	}
 }
+
+func TestResourceAddressHasResourceSpec(t *testing.T) {
+	cases := []struct {
+		Input string
+		Want  bool
+	}{
+		{
+			"module.foo",
+			false,
+		},
+		{
+			"module.foo.module.bar",
+			false,
+		},
+		{
+			"null_resource.baz",
+			true,
+		},
+		{
+			"null_resource.baz[0]",
+			true,
+		},
+		{
+			"data.null_data_source.baz",
+			true,
+		},
+		{
+			"data.null_data_source.baz[0]",
+			true,
+		},
+		{
+			"module.foo.null_resource.baz",
+			true,
+		},
+		{
+			"module.foo.data.null_data_source.baz",
+			true,
+		},
+		{
+			"module.foo.module.bar.null_resource.baz",
+			true,
+		},
+	}
+
+	for _, test := range cases {
+		t.Run(test.Input, func(t *testing.T) {
+			addr, err := ParseResourceAddress(test.Input)
+			if err != nil {
+				t.Fatalf("error parsing address: %s", err)
+			}
+			got := addr.HasResourceSpec()
+			if got != test.Want {
+				t.Fatalf("%q: wrong result %#v; want %#v", test.Input, got, test.Want)
+			}
+		})
+	}
+}