text/template, html/template: nil argument to function yields wrong number of args error #18716
Description
What version of Go are you using (go version)?
go version go1.7.4 darwin/amd64
What operating system and processor architecture are you using (go env)?
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/sethvargo/Development/go"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.7.4_2/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.7.4_2/libexec/pkg/tool/darwin_amd64"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/d0/g1brm3hj0431461p8cxqtjth0000gn/T/go-build267389745=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
What did you do?
https://play.golang.org/p/R3CMVl_nmx
What did you expect to see?
Passing a nested field in a struct that is nil should pass in the zero value for the accepting function. I either expected a different error, or I expected text/template to coerce the value into the signature of the receiving function (string in this case), and use the string zero value.
What did you see instead?
An error is returned indicating an incorrect number of arguments was provided. This is especially confusing because, even if the zero value is provided, the result of the function call should be nil. At worst you're passing nil to a function that accepts a string, but that's not "incorrect number of args", it's a TypeError.
Related Code
From my tracing, the code appears to be here.