text/template: whitespace removal messes up error line numbers

[natefinch]

Please answer these questions before submitting your issue. Thanks!

What did you do?

https://play.golang.org/p/Mx5m92IqPl

Note that the error is on line 4, but is reported on line 3. If you remove the - from the template, the correct error message is reported.

System details

go version go1.9 darwin/amd64
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/finchnat"
GORACE=""
GOROOT="/Users/finchnat/src/github.com/golang/go"
GOTOOLDIR="/Users/finchnat/src/github.com/golang/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/ch/4d1vgsv17jq0b3yfmnkl9thdk0jm7d/T/go-build584589423=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOROOT/bin/go version: go version go1.9 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.9
uname -v: Darwin Kernel Version 16.7.0: Thu Jun 15 17:36:27 PDT 2017; root:xnu-3789.70.16~2/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.12.6
BuildVersion:	16G29
lldb --version: lldb-370.0.42
  Swift-3.1

[mvdan]

I'll take a stab at this; thanks for the reproducer.

[mvdan]

CL sent; this is a regression introduced with whitespace trimming last year.

[gopherbot]

Change https://golang.org/cl/61870 mentions this issue: text/template: fix pos info when trimming newlines