Improve reporting of values with cycles (#217)

Previously, the reporter could handle formatting values with cycles
in that it did not crash with a stack overflow. However, the output
was not particularly understandable as it did not surface to the user
why a particular value was truncated, and if it was truncated due
to a cyclic reference, what was the referent.

This change annotates the reporter tree with pointer information
so that a later pass can inject reference information if it is needed
to produce more understandable output.

Consider the following example:
  	"Foo": &⟪ref#0⟫{
  		Name: "Foo",
  		Bravos: map[string]*cmp_test.CycleBravo{
  			"FooBravo": &{
- 				ID:     101,
+ 				ID:     0,
  				Name:   "FooBravo",
  				Mods:   100,
  				Alphas: {"Foo": &⟪ref#0⟫(...)},

This graph contains a cycle. To ensure that a graph can be formatted,
the cycle is truncated as indicated with: &⟪ref#0⟫(...).
The referent was identified earlier with: &⟪ref#0⟫{...}.
9 files changed
tree: dd32bd59eb58b50d44dee2efa06ac36f8daa92a1
  1. cmp/
  2. .travis.yml
  4. go.mod
  5. go.sum

Package for equality of Go values

GoDev Build Status

This package is intended to be a more powerful and safer alternative to reflect.DeepEqual for comparing whether two values are semantically equal.

The primary features of cmp are:

  • When the default behavior of equality does not suit the needs of the test, custom equality functions can override the equality operation. For example, an equality function may report floats as equal so long as they are within some tolerance of each other.

  • Types that have an Equal method may use that method to determine equality. This allows package authors to determine the equality operation for the types that they define.

  • If no custom equality functions are used and no Equal method is defined, equality is determined by recursively comparing the primitive kinds on both values, much like reflect.DeepEqual. Unlike reflect.DeepEqual, unexported fields are not compared by default; they result in panics unless suppressed by using an Ignore option (see cmpopts.IgnoreUnexported) or explicitly compared using the AllowUnexported option.

See the documentation for more information.

This is not an official Google product.


go get -u


BSD - See LICENSE file