fmt: document existing behavior of nil receivers

If a method called by fmt triggers a panic, the output usually says
so. However, there is heretofore undocumented special treatment for
a panic caused by formatting a nil value with an Error or String
method: the output is simply "<nil>". Document that behavior.

Change-Id: Id0f79dd0b3487f9d1c74a0856727bba5cc342be4
Reviewed-on: https://go-review.googlesource.com/6410
Reviewed-by: David Crawshaw <crawshaw@golang.org>

diff --git a/src/fmt/doc.go b/src/fmt/doc.go
index 9dc2a0d75d807364e7d74e810134befd6e2f21e4..9ba11f4a2ba41ee9317731ac31ff5fe8781afefc 100644 (file)
--- a/src/fmt/doc.go
+++ b/src/fmt/doc.go
@@ -225,7 +225,9 @@
                %!s(PANIC=bad)
 
        The %!s just shows the print verb in use when the failure
-       occurred.
+       occurred. If the panic is caused by a nil receiver to an Error
+       or String method, however, the output is the undecorated
+       string, "<nil>".
 
        Scanning