go/doc: classify function returning slice or array of T as constructor

Previously, go/doc would only consider functions and slices that
return types of T or any number of pointers to T: *T, **T, etc. This
change expands the definition of a constructor to include functions
that return arrays of a type (or pointer to that type) in its first
return.

With this change, the following return types also classify a function
as a constructor of type T:

[1]T
[1]*T
[1]**T
(and so on)

Fixes #22856.

Change-Id: I37957c5f2d6a7b2ceeb3fbaef359057f2039393d
Reviewed-on: https://go-review.googlesource.com/85355
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/go/doc/reader.go

@@ -399,9 +399,9 @@ func (r *reader) readFunc(fun *ast.FuncDecl) {
 			// with the first type in result signature (there may
 			// be more than one result)
 			factoryType := res.Type
-			if t, ok := factoryType.(*ast.ArrayType); ok && t.Len == nil {
-				// We consider functions that return slices of type T (or
-				// pointers to T) as factory functions of T.
+			if t, ok := factoryType.(*ast.ArrayType); ok {
+				// We consider functions that return slices or arrays of type
+				// T (or pointers to T) as factory functions of T.
 				factoryType = t.Elt
 			}
 			if n, imp := baseTypeName(factoryType); !imp && r.isVisible(n) {

src/go/doc/testdata/issue18063.0.golden → src/go/doc/testdata/issue22856.0.golden

 // 
-PACKAGE issue18063
+PACKAGE issue22856
 
 IMPORTPATH
-	testdata/issue18063
+	testdata/issue22856
 
 FILENAMES
-	testdata/issue18063.go
+	testdata/issue22856.go
 
 FUNCTIONS
-	// NewArray is not a factory function because arrays of type T are ...
-	func NewArray() [1]T
-
-	// NewPointerArray is not a factory function because arrays of ...
-	func NewPointerArray() [1]*T
-
 	// NewPointerSliceOfSlice is not a factory function because slices ...
 	func NewPointerSliceOfSlice() [][]*T
 
@@ -31,9 +25,15 @@ TYPES
 	// 
 	func New() T
 
+	// 
+	func NewArray() [1]T
+
 	// 
 	func NewPointer() *T
 
+	// 
+	func NewPointerArray() [1]*T
+
 	// 
 	func NewPointerOfPointer() **T
 

src/go/doc/testdata/issue18063.1.golden → src/go/doc/testdata/issue22856.1.golden

 // 
-PACKAGE issue18063
+PACKAGE issue22856
 
 IMPORTPATH
-	testdata/issue18063
+	testdata/issue22856
 
 FILENAMES
-	testdata/issue18063.go
+	testdata/issue22856.go
 
 FUNCTIONS
-	// NewArray is not a factory function because arrays of type T are ...
-	func NewArray() [1]T
-
-	// NewPointerArray is not a factory function because arrays of ...
-	func NewPointerArray() [1]*T
-
 	// NewPointerSliceOfSlice is not a factory function because slices ...
 	func NewPointerSliceOfSlice() [][]*T
 
@@ -31,9 +25,15 @@ TYPES
 	// 
 	func New() T
 
+	// 
+	func NewArray() [1]T
+
 	// 
 	func NewPointer() *T
 
+	// 
+	func NewPointerArray() [1]*T
+
 	// 
 	func NewPointerOfPointer() **T
 

src/go/doc/testdata/issue18063.2.golden → src/go/doc/testdata/issue22856.2.golden

 // 
-PACKAGE issue18063
+PACKAGE issue22856
 
 IMPORTPATH
-	testdata/issue18063
+	testdata/issue22856
 
 FILENAMES
-	testdata/issue18063.go
+	testdata/issue22856.go
 
 FUNCTIONS
-	// NewArray is not a factory function because arrays of type T are ...
-	func NewArray() [1]T
-
-	// NewPointerArray is not a factory function because arrays of ...
-	func NewPointerArray() [1]*T
-
 	// NewPointerSliceOfSlice is not a factory function because slices ...
 	func NewPointerSliceOfSlice() [][]*T
 
@@ -31,9 +25,15 @@ TYPES
 	// 
 	func New() T
 
+	// 
+	func NewArray() [1]T
+
 	// 
 	func NewPointer() *T
 
+	// 
+	func NewPointerArray() [1]*T
+
 	// 
 	func NewPointerOfPointer() **T
 

src/go/doc/testdata/issue18063.go → src/go/doc/testdata/issue22856.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package issue18063
+package issue22856
 
 type T struct{}
 
@@ -11,13 +11,7 @@ func NewPointer() *T           { return &T{} }
 func NewPointerSlice() []*T    { return []*T{&T{}} }
 func NewSlice() []T            { return []T{T{}} }
 func NewPointerOfPointer() **T { x := &T{}; return &x }
-
-// NewArray is not a factory function because arrays of type T are not
-// factory functions of type T.
 func NewArray() [1]T           { return [1]T{T{}} }
-
-// NewPointerArray is not a factory function because arrays of type *T are not
-// factory functions of type T.
 func NewPointerArray() [1]*T   { return [1]*T{&T{}} }
 
 // NewSliceOfSlice is not a factory function because slices of a slice of