fmt: document that unexported struct fields don't get the String/Error treatment

Fixes #17409.

Change-Id: Ib49ff4a467431b5c1e6637e5144979cf0bfba489
Reviewed-on: https://go-review.googlesource.com/31817
Reviewed-by: Martin Möhrmann <martisch@uos.de>
Reviewed-by: Quentin Smith <quentin@golang.org>

diff --git a/src/fmt/doc.go b/src/fmt/doc.go
index f8ae4e72f9870ff7868d8d87135dd731c457e44b..a2faecb36e1e3f67a04629bfc8af4210d1d4acae 100644 (file)
--- a/src/fmt/doc.go
+++ b/src/fmt/doc.go
@@ -174,6 +174,9 @@
        that type has a String method. Such pathologies are rare, however,
        and the package does not protect against them.
 
+       When printing a struct, fmt cannot and therefore does not invoke
+       formatting methods such as Error or String on unexported fields.
+
        Explicit argument indexes:
 
        In Printf, Sprintf, and Fprintf, the default behavior is for each