From f1a9f1df5070f69685e269de940c6218f899d228 Mon Sep 17 00:00:00 2001
From: Yury Smolsky <yury@smolsky.by>
Date: Wed, 31 Oct 2018 00:19:35 +0200
Subject: [PATCH] go/doc: inspect function signature for building playground
 examples

This documentation example was broken:
https://golang.org/pkg/image/png/#example_Decode.
It did not have the "io" package imported,
The package was referenced in the result type of the function.

The "playExample" function did not inspect
the result types of declared functions.

This CL adds inspecting of parameters and result types of functions.

Fixes #28492
Updates #9679

Change-Id: I6d8b11bad2db8ea8ba69039cfaa914093bdd5132
Reviewed-on: https://go-review.googlesource.com/c/146118
Run-TryBot: Yury Smolsky <yury@smolsky.by>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
---
 src/go/doc/example.go      | 12 ++++++++
 src/go/doc/example_test.go | 62 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/src/go/doc/example.go b/src/go/doc/example.go
index d6d4ece3a8..cf3547810a 100644
--- a/src/go/doc/example.go
+++ b/src/go/doc/example.go
@@ -219,6 +219,18 @@ func playExample(file *ast.File, f *ast.FuncDecl) *ast.File {
 	for i := 0; i < len(depDecls); i++ {
 		switch d := depDecls[i].(type) {
 		case *ast.FuncDecl:
+			// Inspect types of parameters and results. See #28492.
+			if d.Type.Params != nil {
+				for _, p := range d.Type.Params.List {
+					ast.Inspect(p.Type, inspectFunc)
+				}
+			}
+			if d.Type.Results != nil {
+				for _, r := range d.Type.Results.List {
+					ast.Inspect(r.Type, inspectFunc)
+				}
+			}
+
 			ast.Inspect(d.Body, inspectFunc)
 		case *ast.GenDecl:
 			for _, spec := range d.Specs {
diff --git a/src/go/doc/example_test.go b/src/go/doc/example_test.go
index 552a51bf74..0d2bf72e31 100644
--- a/src/go/doc/example_test.go
+++ b/src/go/doc/example_test.go
@@ -351,6 +351,68 @@ func TestExamplesWholeFile(t *testing.T) {
 	}
 }
 
+const exampleInspectSignature = `package foo_test
+
+import (
+	"bytes"
+	"io"
+)
+
+func getReader() io.Reader { return nil }
+
+func do(b bytes.Reader) {}
+
+func Example() {
+	getReader()
+	do()
+	// Output:
+}
+
+func ExampleIgnored() {
+}
+`
+
+const exampleInspectSignatureOutput = `package main
+
+import (
+	"bytes"
+	"io"
+)
+
+func getReader() io.Reader { return nil }
+
+func do(b bytes.Reader) {}
+
+func main() {
+	getReader()
+	do()
+}
+`
+
+func TestExampleInspectSignature(t *testing.T) {
+	// Verify that "bytes" and "io" are imported. See issue #28492.
+	fset := token.NewFileSet()
+	file, err := parser.ParseFile(fset, "test.go", strings.NewReader(exampleInspectSignature), parser.ParseComments)
+	if err != nil {
+		t.Fatal(err)
+	}
+	es := doc.Examples(file)
+	if len(es) != 2 {
+		t.Fatalf("wrong number of examples; got %d want 2", len(es))
+	}
+	// We are interested in the first example only.
+	e := es[0]
+	if e.Name != "" {
+		t.Errorf("got Name == %q, want %q", e.Name, "")
+	}
+	if g, w := formatFile(t, fset, e.Play), exampleInspectSignatureOutput; g != w {
+		t.Errorf("got Play == %q, want %q", g, w)
+	}
+	if g, w := e.Output, ""; g != w {
+		t.Errorf("got Output == %q, want %q", g, w)
+	}
+}
+
 func formatFile(t *testing.T, fset *token.FileSet, n *ast.File) string {
 	if n == nil {
 		return "<nil>"
-- 
2.50.0