typecheck: display compilation errors as report instead of error

[ldez]

This PR will improve the report when the analyzed code contains compilation errors.

It's a bit complex to explain but I will try to explain it.

typecheck is like the front-end of a Go compiler: parses and type-checks Go code, this "linter" can manage compilation errors, that's its role.

typecheck is not a real linter it's just a way to parse some errors produced by the types.Checker.
The code in pkg/golinters/typecheck.go is just a kind of placeholder.

golangci-lint/pkg/golinters/typecheck.go

Lines 14 to 16 in 8db518c

	Run: func(pass *analysis.Pass) (interface{}, error) {
	return nil, nil
	},

The real code is here:

golangci-lint/pkg/golinters/goanalysis/linter.go

Lines 180 to 216 in 8db518c

	func parseError(srcErr packages.Error) (*result.Issue, error) {
	pos, err := libpackages.ParseErrorPosition(srcErr.Pos)
	if err != nil {
	return nil, err
	}
	return &result.Issue{
	Pos: *pos,
	Text: srcErr.Msg,
	FromLinter: "typecheck",
	}, nil
	}
	func buildIssuesFromErrorsForTypecheckMode(errs []error, lintCtx *linter.Context) ([]result.Issue, error) {
	var issues []result.Issue
	uniqReportedIssues := map[string]bool{}
	for _, err := range errs {
	itErr, ok := errors.Cause(err).(*IllTypedError)
	if !ok {
	return nil, err
	}
	for _, err := range libpackages.ExtractErrors(itErr.Pkg) {
	i, perr := parseError(err)
	if perr != nil { // failed to parse
	if uniqReportedIssues[err.Msg] {
	continue
	}
	uniqReportedIssues[err.Msg] = true
	lintCtx.Log.Errorf("typechecking error: %s", err.Msg)
	} else {
	i.Pkg = itErr.Pkg // to save to cache later
	issues = append(issues, *i)
	}
	}
	}
	return issues, nil
	}

The core of the fix is to always handle errors as issues if the errors are IllTypedError.
And to be able to detect this kind of error, I dropped the FailedPrerequisitesError because it grouped errors as string instead of error.

This applies to all linters 🎉

I improved the number of issues reported by typecheck by removing the duplicate elements with a "stack crusher", so now the hardcoded limit can be removed safely.

I have split the pkg/golinters/goanalysis/runner.go file into multiple files because it's a pain to debug a 1500 lines file with recursive calls, multiple structures, and multiple embedded and anonymous functions.

Fixes #1820
Fixes #1826
Fixes #1168
Fixes #1043
Fixes #1002
Fixes #886

I think this also partially fixes #1792 (#1792 (comment))

Before my PR

$ golangci-lint run
WARN [runner] Can't run linter goanalysis_metalinter: bodyclose: failed prerequisites: [buildssa@github.com/golangci/golangci-lint/pkg/lint: analysis skipped: errors in package: [/home/ldez/sources/go/src/github.com/golangci/golangci-lint/pkg/lint/runner.go:18:2: could not import github.com/golangci/golangci-lint/pkg/lint/lintersdb (/home/ldez/sources/go/src/github.com/golangci/golangci-lint/pkg/lint/lintersdb/manager.go:13:2: could not import github.com/golangci/golangci-lint/pkg/golinters (/home/ldez/sources/go/src/github.com/golangci/golangci-lint/pkg/golinters/deadcode.go:21:9: undeclared name: linterName)) /home/ldez/sources/go/src/github.com/golangci/golangci-lint/pkg/lint/runner.go:22:2: could not import github.com/golangci/golangci-lint/pkg/result/processors (/home/ldez/sources/go/src/github.com/golangci/golangci-lint/pkg/result/processors/nolint.go:11:2: could not import github.com/golangci/golangci-lint/pkg/golinters (/home/ldez/sources/go/src/github.com/golangci/golangci-lint/pkg/golinters/deadcode.go:21:9: undeclared name: linterName))]] 
WARN [runner] Can't run linter unused: buildir: failed to load package golinters: could not load export data: no export data for "github.com/golangci/golangci-lint/pkg/golinters" 
ERRO Running error: buildir: failed to load package golinters: could not load export data: no export data for "github.com/golangci/golangci-lint/pkg/golinters" 

With my PR

$ ./golangci-lint run
pkg/golinters/deadcode.go:21:9: undeclared name: `linterName` (typecheck)
                Name: linterName,
                      ^
pkg/golinters/deadcode.go:34:18: undeclared name: `linterName` (typecheck)
                                        FromLinter: linterName,
                                                    ^
pkg/golinters/deadcode.go:45:3: undeclared name: `linterName` (typecheck)
                linterName,
                ^
pkg/lint/lintersdb/manager.go:500:2: isLocalRun declared but not used (typecheck)
        isLocalRun := os.Getenv("GOLANGCI_COM_RUN") == ""
        ^

[bombsimon]

Awesome job, thanks for fixing this! Also thanks for nicely splitting this up across several commits so I could easy follow them and not mix restructuring of the code with your changes to fix this. This will be much appreciated!

🌟 🌟 🌟

[ldez]

@thebeline could you open a new issue?

[thebeline]

@ldez - I would love to, but I am not exactly sure what I am reporting on, how to phrase it, etc.

[ldez]

@thebeline I will open a new issue BUT please provide a way to reproduce it.