cmd/doc: add a -src flag to show original source

It's long-desired but was blocked by #26835. That is now fixed, so
it's easy. When -src is off, we behave as before. But with -src
set, initialize the go/doc package to preserve the original AST and
things flow very easily.

With -src, since you're seeing inside the package source anyway it
shows unexported fields and constants: you see the original source.
But you still need -u to ask about them.

Fixes #18807

Change-Id: I473e90323b4eff0735360274dc0d2d9dba16ff8b
Reviewed-on: https://go-review.googlesource.com/c/140959
Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/src/cmd/doc/testdata/pkg.go b/src/cmd/doc/testdata/pkg.go
index bc069939f8..50105b5fcc 100644
--- a/src/cmd/doc/testdata/pkg.go
+++ b/src/cmd/doc/testdata/pkg.go
@@ -5,6 +5,8 @@
 // Package comment.
 package pkg
 
+import "io"
+
 // Constants
 
 // Comment about exported constant.
@@ -52,7 +54,9 @@ var (
 )
 
 // Comment about exported function.
-func ExportedFunc(a int) bool
+func ExportedFunc(a int) bool {
+	return true != false
+}
 
 // Comment about internal function.
 func internalFunc(a int) bool
@@ -73,7 +77,7 @@ type ExportedType struct {
 
 // Comment about exported method.
 func (ExportedType) ExportedMethod(a int) bool {
-	return true
+	return true != true
 }
 
 // Comment about unexported method.