go/doc: support examples on methods from embedded unexported types

In

  type T1 struct { t2 }
  type t2 int
  func (t2) M()

T1 has method M because it embeds t2, which has M. Classify
the example

  func ExampleT1_M

with T1 instead of ignoring it, as is done currently. There is no
other way to provide an example for such a method, since its original
type is unexported.

Continue to ignore examples on methods from embedded types that are
exported, unless in AllMethods mode. Examples for those methods could
be written on the original type.

The change involves removing a check in classifyExamples. The check
isn't necessary to get the above behavior because
reader.collectEmbeddedMethods and sortedFuncs already generate the
appropriate list of methods.

For #40172.

Change-Id: Ibe7d965ecba6426466184e6e6655fc05989e9caf
Reviewed-on: https://go-review.googlesource.com/c/go/+/249557
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: jba

src/go/doc/example.go

@@ -486,7 +486,7 @@ func classifyExamples(p *Package, examples []*Example) {
 			ids[f.Name] = &f.Examples
 		}
 		for _, m := range t.Methods {
-			if !token.IsExported(m.Name) || m.Level != 0 { // avoid forwarded methods from embedding
+			if !token.IsExported(m.Name) {
 				continue
 			}
 			ids[strings.TrimPrefix(m.Recv, "*")+"_"+m.Name] = &m.Examples

src/go/doc/example_test.go

@@ -563,6 +563,7 @@ type (
 	type2     int
 
 	Embed struct { Type1 }
+	Uembed struct { type2 }
 )
 
 func Func1()     {}
@@ -575,6 +576,8 @@ func (Type1) Func1_Foo() {}
 func (Type1) Func1_foo() {}
 func (Type1) func2() {}
 
+func (type2) Func1() {}
+
 type (
 	Conflict          int
 	Conflict_Conflict int
@@ -633,7 +636,9 @@ func ExampleType1_Func1_foo_suffix()    {}
 func ExampleType1_Func1_foo_Suffix()    {} // matches Type1.Func1, instead of Type1.Func1_foo
 func ExampleType1_func2()               {} // matches Type1, instead of Type1.func2
 
-func ExampleEmbed_Func1() {} // invalid - no support for forwarded methods from embedding
+func ExampleEmbed_Func1()         {} // invalid - no support for forwarded methods from embedding exported type
+func ExampleUembed_Func1()        {} // methods from embedding unexported types are OK
+func ExampleUembed_Func1_suffix() {}
 
 func ExampleConflict_Conflict()        {} // ambiguous with either Conflict or Conflict_Conflict type
 func ExampleConflict_conflict()        {} // ambiguous with either Conflict or Conflict_conflict type
@@ -683,6 +688,8 @@ func ExampleConflict_conflict_suffix() {} // ambiguous with either Conflict or C
 		"Type1.Func1_Foo": {"", "suffix"},
 		"Type1.Func1_foo": {"", "suffix"},
 
+		"Uembed.Func1": {"", "suffix"},
+
 		// These are implementation dependent due to the ambiguous parsing.
 		"Conflict_Conflict": {"", "suffix"},
 		"Conflict_conflict": {"", "suffix"},