x/tools/go/analysis/analysistest: facts are sometimes not inherited from dependent analyzers

[ericchiang]

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

% go version
go version go1.20.2 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/ericchiang/Library/Caches/go-build" GOENV="/Users/ericchiang/Library/Application Support/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="amd64" GOHOSTOS="darwin" GOINSECURE="" GOMODCACHE="/Users/ericchiang/go/pkg/mod" GONOPROXY="" GONOSUMDB="" GOOS="darwin" GOPATH="/Users/ericchiang/go" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/usr/local/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64" GOVCS="" GOVERSION="go1.20.2" GCCGO="gccgo" GOAMD64="v1" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="/dev/null" GOWORK="" CGO_CFLAGS="-O2 -g" CGO_CPPFLAGS="" CGO_CXXFLAGS="-O2 -g" CGO_FFLAGS="-O2 -g" CGO_LDFLAGS="-O2 -g" PKG_CONFIG="pkg-config" GOGCCFLAGS="-fPIC -arch x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/d1/wpvcpdrs2tlgn5xs3_xm88th0000gn/T/go-build2810425986=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Wrote an analyzer that depends on facts from another analyzer. In my case, this was a dead code analyzer that depended on facts omitted by a "usage" analyzer. Per the docs in the analysis package:

https://pkg.go.dev/golang.org/x/tools/go/analysis#hdr-Modular_analysis_with_Facts

I modeled this as an analyzer that read facts from another.

However, when I tried to test with analysistest, the analyzer wasn't seeing the facts:

package main

import (
        "testing"

        "golang.org/x/tools/go/analysis"
        "golang.org/x/tools/go/analysis/analysistest"
)

var file = `package a
func b() {} // want "test message"
`

type fact struct{ Message string }

func (f *fact) AFact() {}

var factAnalyzer = &analysis.Analyzer{
        Name:      "dependent",
        FactTypes: []analysis.Fact{&fact{}},
        Run: func(pass *analysis.Pass) (interface{}, error) {
                o := pass.Pkg.Scope().Lookup("b")
                pass.ExportObjectFact(o, &fact{Message: "test message"})
                return nil, nil
        },
}

var analyzer = &analysis.Analyzer{
        Name:      "analyzer",
        FactTypes: []analysis.Fact{&fact{}},
        Requires:  []*analysis.Analyzer{factAnalyzer},
        Run: func(pass *analysis.Pass) (interface{}, error) {
                o := pass.Pkg.Scope().Lookup("b")
                var f fact
                if !pass.ImportObjectFact(o, &f) {
                        return nil, nil
                }
                pass.Report(analysis.Diagnostic{Pos: o.Pos(), Message: f.Message})
                return nil, nil
        },
}

func TestAnalyze(t *testing.T) {
        files := map[string]string{"a/a.go": file}
        dir, cleanup, err := analysistest.WriteFiles(files)
        if err != nil {
                t.Fatalf("writing temp files")
        }
        defer cleanup()
        analysistest.Run(t, dir, analyzer, "a")
}

What did you expect to see?

Analyzer to see the facts exported by the "factAnalyzer".

What did you see instead?

It appears that when analyzing the same package, facts aren't inherited:

https://github.com/golang/tools/blob/fa556487c5c2be818dd2bab43e16f1afa06f8f89/go/analysis/internal/checker/checker.go#L721-L732

So the test fails:

% go test
--- FAIL: TestAnalyze (0.07s)
    analysistest.go:520: a/a.go:2: no diagnostic was reported matching `test message`
FAIL
exit status 1
FAIL	example.com/m	0.368s

[heschi]

cc @timothy-king @adonovan

[adonovan]

Wrote an analyzer that depends on facts from another analyzer.

If you turn your test into a standalone checker command (e.g. using singlechecker), you'll immediately notice that it fails an assertion at startup:

analyzer: fact type *fact registered by two analyzers: dependent, analyzer

Facts allow one analyzer to save (serialized) information computed during analysis of a lower package and retrieve it when that same analyzer inspects a higher package, even when the two units of analysis occur in different processes. Facts are a private implementation detail of an analyzer; an analyzer cannot retrieve facts written by a different analyzer. The Validate function called within singlechecker reports the mistake, but unfortunately the analyzertest package failed to call Validate. I'll fix that presently. Thanks for reporting the problem.

The way to accomplish your goal is not to try to share facts between analyzers, but to return a Result from the 'dependent' Analyzer and to Require it from the 'analyzer' Analyzer. A Result is an arbitrary data structure--it needn't be serializable--so it could be a set of types.Objects with any desired property. Each time you import a fact about object o, you could add it to the set, and each time you infer that some new object has the property, you could add it to the set (as well as exporting a fact). Facts are for "vertical" communication, results are for "horizontal" communication.

[gopherbot]

Change https://go.dev/cl/479737 mentions this issue: go/analysis/analysistest: Validate analyzers in Run

[ericchiang]

This is really helpful, thanks! I'll rejigger my analyzer and see if I can get it working with results.

Closing out, and glad the error message is clearer now.