cmd/doc, go/doc: add basic support for generic code

Update cmd/doc and go/doc for the generics, by adding handling for type
parameters and the new embedded interface elements.

Specifically:
 - Format type parameters when summarizing type and function nodes.
 - Find the origin type name for instantiation expressions, so that
   methods are associated with generic type declarations.
 - Generalize the handling of embedding 'error' in interfaces to
   arbitrary predeclared types.
 - Keep embedded type literals.
 - Update filtering to descend into embedded type literals.

Also add "any" to the list of predeclared types.

Updates #49210

Change-Id: I6ea82869f19c3cdbc3c842f01581c8fc7e1c2ee7
Reviewed-on: https://go-review.googlesource.com/c/go/+/359778
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

1 files changed, 17 insertions, 4 deletions

diff --git a/src/cmd/doc/pkg.go b/src/cmd/doc/pkg.go
index 822c9e16f8..2257c5c0eb 100644
--- a/src/cmd/doc/pkg.go
+++ b/src/cmd/doc/pkg.go
@@ -323,7 +323,8 @@ func (pkg *Package) oneLineNodeDepth(node ast.Node, depth int) string {
 		if n.Assign.IsValid() {
 			sep = " = "
 		}
-		return fmt.Sprintf("type %s%s%s", n.Name.Name, sep, pkg.oneLineNodeDepth(n.Type, depth))
+		tparams := pkg.formatTypeParams(n.TypeParams, depth)
+		return fmt.Sprintf("type %s%s%s%s", n.Name.Name, tparams, sep, pkg.oneLineNodeDepth(n.Type, depth))
 
 	case *ast.FuncType:
 		var params []string
@@ -342,15 +343,16 @@ func (pkg *Package) oneLineNodeDepth(node ast.Node, depth int) string {
 			}
 		}
 
+		tparam := pkg.formatTypeParams(n.TypeParams, depth)
 		param := joinStrings(params)
 		if len(results) == 0 {
-			return fmt.Sprintf("func(%s)", param)
+			return fmt.Sprintf("func%s(%s)", tparam, param)
 		}
 		result := joinStrings(results)
 		if !needParens {
-			return fmt.Sprintf("func(%s) %s", param, result)
+			return fmt.Sprintf("func%s(%s) %s", tparam, param, result)
 		}
-		return fmt.Sprintf("func(%s) (%s)", param, result)
+		return fmt.Sprintf("func%s(%s) (%s)", tparam, param, result)
 
 	case *ast.StructType:
 		if n.Fields == nil || len(n.Fields.List) == 0 {
@@ -419,6 +421,17 @@ func (pkg *Package) oneLineNodeDepth(node ast.Node, depth int) string {
 	}
 }
 
+func (pkg *Package) formatTypeParams(list *ast.FieldList, depth int) string {
+	if list.NumFields() == 0 {
+		return ""
+	}
+	var tparams []string
+	for _, field := range list.List {
+		tparams = append(tparams, pkg.oneLineField(field, depth))
+	}
+	return "[" + joinStrings(tparams) + "]"
+}
+
 // oneLineField returns a one-line summary of the field.
 func (pkg *Package) oneLineField(field *ast.Field, depth int) string {
 	var names []string