gopls: return file error if file open fails

The bug manifests itself when a non-existent file is passed in as an
argument to gopls, causing a nil pointer dereference panic. This is due
to an attempt to reference the "mapper" attribute, which is not set if
the file is not found.

The resolution is to check for an informative error that is set on the
file instance after "getFile" is called and return it immediately to the
caller to allow the error to propagate up to the main() function and
print the error to stdout.

Testing:
--------

Non-existent file:
$ gopls -rpc.trace -v check gopls/doesnotexist.go
check: file:///Users/albertteoh/repo/tools/gopls/doesnotexist.go: open /Users/albertteoh/repo/tools/gopls/doesnotexist.go: no such file or directory

Existing go file:
$ gopls -rpc.trace -v check internal/lsp/definition.go
2019/08/03 13:33:00 Info:go/packages.Load
	packages = 2
2019/08/03 13:33:00 Info:go/packages.Load
	package = golang.org/x/tools/internal/lsp
...

Fixes golang/go#33445

Change-Id: Ib56d8a4b7f23f4882b75cf684c5d18a49d27b824
Reviewed-on: https://go-review.googlesource.com/c/tools/+/188857
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>
1 file changed
tree: 596317cfb0f609844177bba6ad47d9e0f2342f5c
  1. benchmark/
  2. blog/
  3. cmd/
  4. container/
  5. cover/
  6. go/
  7. godoc/
  8. gopls/
  9. imports/
  10. internal/
  11. playground/
  12. present/
  13. refactor/
  14. .gitattributes
  15. .gitignore
  16. AUTHORS
  17. codereview.cfg
  18. CONTRIBUTING.md
  19. CONTRIBUTORS
  20. go.mod
  21. go.sum
  22. LICENSE
  23. PATENTS
  24. README.md
README.md

Go Tools

This subrepository holds the source for various packages and tools that support the Go programming language.

Some of the tools, godoc and vet for example, are included in binary Go distributions.

Others, including the Go guru and the test coverage tool, can be fetched with go get.

Packages include a type-checker for Go and an implementation of the Static Single Assignment form (SSA) representation for Go programs.

Download/Install

The easiest way to install is to run go get -u golang.org/x/tools/.... You can also manually git clone the repository to $GOPATH/src/golang.org/x/tools.

Report Issues / Send Patches

This repository uses Gerrit for code changes. To learn how to submit changes to this repository, see https://golang.org/doc/contribute.html.

The main issue tracker for the tools repository is located at https://github.com/golang/go/issues. Prefix your issue with “x/tools/(your subdir):” in the subject line, so it is easy to find.