What I want to achieve

I want to write tests for analyzers that utilize packages.Module information.

x/tools/go/analysis/analysistest provides helper functions for testing go/analysis analyzers.

// It loads the packages from the specified GOPATH-style project
// directory using golang.org/x/tools/go/packages, ...
func Run(t Testing, dir string, a *analysis.Analyzer, patterns ...string) []*Result

// RunWithSuggestedFixes behaves like Run, ...
func RunWithSuggestedFixes(t Testing, dir string, a *analysis.Analyzer, patterns ...string) []*Result

• Run and RunWithSuggestedFixes internally call go/packages.Load but explicitly in GOPATH mode.
• The dir is supposed to be GOPATH, which doesn't apply in module mode.
• packages.Config is not accepted.

These limit the utility of the package when authoring module-aware analyzers.

What I propose

I propose to add module-friendly test helpers. Something like:

func TestAnalyzer(t Testing, a *analysis.Analyzer, pkgs *[]packages.Package) []*Result

or

func TestAnalyzer(t Testing, a *analysis.Analyzer, cfg *packages.Config, patterns ...string) []*Result

Alternatives to consider

GOPATH style project layout is easy and convenient. For the last half decade, nobody
complained about this issue, which indicates supporting module mode in this package is not
important. My analyzer is not a typical one.

So I considered -

1. Refactor and move the core of x/tools/go/analysis/analysistest to x/tools/internal/analysisinternal/.... Unfortunately, I see this will cause move of x/tools/go/analysis/internal/checker and analysisflags. I like containing analysis specific internal logic under x/tools/go/analysis/internal and am not sure about this big move.

2. Make part of analysistest.Run available through a var in x/tools/internal/analysisinternal/... that's set by analysistest init. See CL408375 This is a smaller change than 2, but documentation for the type aliased analysistest.Testing and checker.TestAnalyzerResult isn't great.

What about WriteFiles

It also supports only GOPATH mode. WriteFiles can be potentially replaced with go/packages/packagestest.

// WriteFiles is a helper function that creates a temporary directory
// and populates it with a GOPATH-style project using filemap...
func WriteFiles(filemap map[string]string) (dir string, cleanup func(), err error)

But for a simple analyzer test, this is more convenient than the helpers in go/packages/packagestest.

cc @golang/tools-team