x/tools/present: unexpected eof on slide header only

[tz70s]

What version of Go are you using (go version)?

$ go version
go version go1.14.4 darwin/amd64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/tz70s/Library/Caches/go-build"
GOENV="/Users/tz70s/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/tz70s/WorkSpace/golang/golang"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.14.4/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.14.4/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/f9/zc8k9cr145557jz3bqwmsz880000gn/T/go-build573678616=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

The present tool assume an implicit behavior that the header & the content (next slide page) should exist simultaneously.

E.g. if we have such slide file:

# Go present tool
Present tool reproducer
Tags: go, tool

Tzu-Chiao Yeh
5 Jul 2020
su3g4284zo6y7@gmail.com

instead of

# Go present tool
Present tool reproducer
Tags: go, tool

Tzu-Chiao Yeh
5 Jul 2020
su3g4284zo6y7@gmail.com

## Slide page

We'll get an 'unexpected eof' error.

What did you expect to see?

This error message can lead user confusing:

• Actually legacy syntax will have the same issue as well.
• Ideally the "header-only" behavior is acceptable due to usually we start to write the first slide.
• Document somewhere (sorry if I missed it) and provide better error message would be helpful if this behavior is not acceptable.

What did you see instead?

'unexpected eof' error

Actually this issue can be divided into two scenarios:

• Provided header but no author and no sections.
• Provided header and author but no sections.

I think a simple improvement is just skip sections when we reach eof on header or author?

[gopherbot]

Change https://golang.org/cl/240977 mentions this issue: present: allow header and author only format

[dmitshur]

/cc @rsc per owners.