package lint

/*
Parallelism

Runner implements parallel processing of packages by spawning one
goroutine per package in the dependency graph, without any semaphores.
Each goroutine initially waits on the completion of all of its
dependencies, thus establishing correct order of processing. Once all
dependencies finish processing, the goroutine will load the package
from export data or source – this loading is guarded by a semaphore,
sized according to the number of CPU cores. This way, we only have as
many packages occupying memory and CPU resources as there are actual
cores to process them.

This combination of unbounded goroutines but bounded package loading
means that if we have many parallel, independent subgraphs, they will
all execute in parallel, while not wasting resources for long linear
chains or trying to process more subgraphs in parallel than the system
can handle.

*/

import (
	"bytes"
	"encoding/gob"
	"encoding/hex"
	"fmt"
	"go/ast"
	"go/token"
	"go/types"
	"reflect"
	"regexp"
	"runtime"
	"sort"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"

	"golang.org/x/tools/go/analysis"
	"golang.org/x/tools/go/packages"
	"golang.org/x/tools/go/types/objectpath"
	"honnef.co/go/tools/config"
	"honnef.co/go/tools/facts"
	"honnef.co/go/tools/internal/cache"
	"honnef.co/go/tools/loader"
)

// If enabled, abuse of the go/analysis API will lead to panics
const sanityCheck = true

// OPT(dh): for a dependency tree A->B->C->D, if we have cached data
// for B, there should be no need to load C and D individually. Go's
// export data for B contains all the data we need on types, and our
// fact cache could store the union of B, C and D in B.
//
// This may change unused's behavior, however, as it may observe fewer
// interfaces from transitive dependencies.

type Package struct {
	dependents uint64

	*packages.Package
	Imports    []*Package
	initial    bool
	fromSource bool
	hash       string
	done       chan struct{}

	resultsMu sync.Mutex
	// results maps analyzer IDs to analyzer results
	results []*result

	cfg      *config.Config
	gen      map[string]facts.Generator
	problems []Problem
	ignores  []Ignore
	errs     []error

	// these slices are indexed by analysis
	facts    []map[types.Object][]analysis.Fact
	pkgFacts [][]analysis.Fact

	canClearTypes bool
}

func (pkg *Package) decUse() {
	atomic.AddUint64(&pkg.dependents, ^uint64(0))
	if atomic.LoadUint64(&pkg.dependents) == 0 {
		// nobody depends on this package anymore
		if pkg.canClearTypes {
			pkg.Types = nil
		}
		pkg.facts = nil
		pkg.pkgFacts = nil

		for _, imp := range pkg.Imports {
			imp.decUse()
		}
	}
}

type result struct {
	v     interface{}
	err   error
	ready chan struct{}
}

type Runner struct {
	ld    loader.Loader
	cache *cache.Cache

	analyzerIDs analyzerIDs

	// limits parallelism of loading packages
	loadSem chan struct{}

	goVersion int
	stats     *Stats
}

type analyzerIDs struct {
	m map[*analysis.Analyzer]int
}

func (ids analyzerIDs) get(a *analysis.Analyzer) int {
	id, ok := ids.m[a]
	if !ok {
		panic(fmt.Sprintf("no analyzer ID for %s", a.Name))
	}
	return id
}

type Fact struct {
	Path string
	Fact analysis.Fact
}

type analysisAction struct {
	analyzer        *analysis.Analyzer
	analyzerID      int
	pkg             *Package
	newPackageFacts []analysis.Fact
	problems        []Problem

	pkgFacts map[*types.Package][]analysis.Fact
}

func (ac *analysisAction) String() string {
	return fmt.Sprintf("%s @ %s", ac.analyzer, ac.pkg)
}

func (ac *analysisAction) allObjectFacts() []analysis.ObjectFact {
	out := make([]analysis.ObjectFact, 0, len(ac.pkg.facts[ac.analyzerID]))
	for obj, facts := range ac.pkg.facts[ac.analyzerID] {
		for _, fact := range facts {
			out = append(out, analysis.ObjectFact{
				Object: obj,
				Fact:   fact,
			})
		}
	}
	return out
}

func (ac *analysisAction) allPackageFacts() []analysis.PackageFact {
	out := make([]analysis.PackageFact, 0, len(ac.pkgFacts))
	for pkg, facts := range ac.pkgFacts {
		for _, fact := range facts {
			out = append(out, analysis.PackageFact{
				Package: pkg,
				Fact:    fact,
			})
		}
	}
	return out
}

func (ac *analysisAction) importObjectFact(obj types.Object, fact analysis.Fact) bool {
	if sanityCheck && len(ac.analyzer.FactTypes) == 0 {
		panic("analysis doesn't export any facts")
	}
	for _, f := range ac.pkg.facts[ac.analyzerID][obj] {
		if reflect.TypeOf(f) == reflect.TypeOf(fact) {
			reflect.ValueOf(fact).Elem().Set(reflect.ValueOf(f).Elem())
			return true
		}
	}
	return false
}

func (ac *analysisAction) importPackageFact(pkg *types.Package, fact analysis.Fact) bool {
	if sanityCheck && len(ac.analyzer.FactTypes) == 0 {
		panic("analysis doesn't export any facts")
	}
	for _, f := range ac.pkgFacts[pkg] {
		if reflect.TypeOf(f) == reflect.TypeOf(fact) {
			reflect.ValueOf(fact).Elem().Set(reflect.ValueOf(f).Elem())
			return true
		}
	}
	return false
}

func (ac *analysisAction) exportObjectFact(obj types.Object, fact analysis.Fact) {
	if sanityCheck && len(ac.analyzer.FactTypes) == 0 {
		panic("analysis doesn't export any facts")
	}
	ac.pkg.facts[ac.analyzerID][obj] = append(ac.pkg.facts[ac.analyzerID][obj], fact)
}

func (ac *analysisAction) exportPackageFact(fact analysis.Fact) {
	if sanityCheck && len(ac.analyzer.FactTypes) == 0 {
		panic("analysis doesn't export any facts")
	}
	ac.pkgFacts[ac.pkg.Types] = append(ac.pkgFacts[ac.pkg.Types], fact)
	ac.newPackageFacts = append(ac.newPackageFacts, fact)
}

func (ac *analysisAction) report(pass *analysis.Pass, d analysis.Diagnostic) {
	p := Problem{
		Pos:     DisplayPosition(pass.Fset, d.Pos),
		End:     DisplayPosition(pass.Fset, d.End),
		Message: d.Message,
		Check:   pass.Analyzer.Name,
	}
	ac.problems = append(ac.problems, p)
}

func (r *Runner) runAnalysis(ac *analysisAction) (ret interface{}, err error) {
	ac.pkg.resultsMu.Lock()
	res := ac.pkg.results[r.analyzerIDs.get(ac.analyzer)]
	if res != nil {
		ac.pkg.resultsMu.Unlock()
		<-res.ready
		return res.v, res.err
	} else {
		res = &result{
			ready: make(chan struct{}),
		}
		ac.pkg.results[r.analyzerIDs.get(ac.analyzer)] = res
		ac.pkg.resultsMu.Unlock()

		defer func() {
			res.v = ret
			res.err = err
			close(res.ready)
		}()

		pass := new(analysis.Pass)
		*pass = analysis.Pass{
			Analyzer: ac.analyzer,
			Fset:     ac.pkg.Fset,
			Files:    ac.pkg.Syntax,
			// type information may be nil or may be populated. if it is
			// nil, it will get populated later.
			Pkg:               ac.pkg.Types,
			TypesInfo:         ac.pkg.TypesInfo,
			TypesSizes:        ac.pkg.TypesSizes,
			ResultOf:          map[*analysis.Analyzer]interface{}{},
			ImportObjectFact:  ac.importObjectFact,
			ImportPackageFact: ac.importPackageFact,
			ExportObjectFact:  ac.exportObjectFact,
			ExportPackageFact: ac.exportPackageFact,
			Report: func(d analysis.Diagnostic) {
				ac.report(pass, d)
			},
			AllObjectFacts:  ac.allObjectFacts,
			AllPackageFacts: ac.allPackageFacts,
		}

		if !ac.pkg.initial {
			// Don't report problems in dependencies
			pass.Report = func(analysis.Diagnostic) {}
		}
		return r.runAnalysisUser(pass, ac)
	}
}

func (r *Runner) loadCachedFacts(a *analysis.Analyzer, pkg *Package) ([]Fact, bool) {
	if len(a.FactTypes) == 0 {
		return nil, true
	}

	var facts []Fact
	// Look in the cache for facts
	aID, err := passActionID(pkg, a)
	if err != nil {
		return nil, false
	}
	aID = cache.Subkey(aID, "facts")
	b, _, err := r.cache.GetBytes(aID)
	if err != nil {
		// No cached facts, analyse this package like a user-provided one, but ignore diagnostics
		return nil, false
	}

	if err := gob.NewDecoder(bytes.NewReader(b)).Decode(&facts); err != nil {
		// Cached facts are broken, analyse this package like a user-provided one, but ignore diagnostics
		return nil, false
	}
	return facts, true
}

type dependencyError struct {
	dep string
	err error
}

func (err dependencyError) nested() dependencyError {
	if o, ok := err.err.(dependencyError); ok {
		return o.nested()
	}
	return err
}

func (err dependencyError) Error() string {
	if o, ok := err.err.(dependencyError); ok {
		return o.Error()
	}
	return fmt.Sprintf("error running dependency %s: %s", err.dep, err.err)
}

func (r *Runner) makeAnalysisAction(a *analysis.Analyzer, pkg *Package) *analysisAction {
	aid := r.analyzerIDs.get(a)
	ac := &analysisAction{
		analyzer:   a,
		analyzerID: aid,
		pkg:        pkg,
	}

	if len(a.FactTypes) == 0 {
		return ac
	}

	// Merge all package facts of dependencies
	ac.pkgFacts = map[*types.Package][]analysis.Fact{}
	seen := map[*Package]struct{}{}
	var dfs func(*Package)
	dfs = func(pkg *Package) {
		if _, ok := seen[pkg]; ok {
			return
		}
		seen[pkg] = struct{}{}
		s := pkg.pkgFacts[aid]
		ac.pkgFacts[pkg.Types] = s[0:len(s):len(s)]
		for _, imp := range pkg.Imports {
			dfs(imp)
		}
	}
	dfs(pkg)

	return ac
}

// analyzes that we always want to run, even if they're not being run
// explicitly or as dependencies. these are necessary for the inner
// workings of the runner.
var injectedAnalyses = []*analysis.Analyzer{facts.Generated, config.Analyzer}

func (r *Runner) runAnalysisUser(pass *analysis.Pass, ac *analysisAction) (interface{}, error) {
	if !ac.pkg.fromSource {
		panic(fmt.Sprintf("internal error: %s was not loaded from source", ac.pkg))
	}

	// User-provided package, analyse it
	// First analyze it with dependencies
	for _, req := range ac.analyzer.Requires {
		acReq := r.makeAnalysisAction(req, ac.pkg)
		ret, err := r.runAnalysis(acReq)
		if err != nil {
			// We couldn't run a dependency, no point in going on
			return nil, dependencyError{req.Name, err}
		}

		pass.ResultOf[req] = ret
	}

	// Then with this analyzer
	ret, err := ac.analyzer.Run(pass)
	if err != nil {
		return nil, err
	}

	if len(ac.analyzer.FactTypes) > 0 {
		// Merge new facts into the package and persist them.
		var facts []Fact
		for _, fact := range ac.newPackageFacts {
			id := r.analyzerIDs.get(ac.analyzer)
			ac.pkg.pkgFacts[id] = append(ac.pkg.pkgFacts[id], fact)
			facts = append(facts, Fact{"", fact})
		}
		for obj, afacts := range ac.pkg.facts[ac.analyzerID] {
			if obj.Pkg() != ac.pkg.Package.Types {
				continue
			}
			path, err := objectpath.For(obj)
			if err != nil {
				continue
			}
			for _, fact := range afacts {
				facts = append(facts, Fact{string(path), fact})
			}
		}

		buf := &bytes.Buffer{}
		if err := gob.NewEncoder(buf).Encode(facts); err != nil {
			return nil, err
		}
		aID, err := passActionID(ac.pkg, ac.analyzer)
		if err != nil {
			return nil, err
		}
		aID = cache.Subkey(aID, "facts")
		if err := r.cache.PutBytes(aID, buf.Bytes()); err != nil {
			return nil, err
		}
	}

	return ret, nil
}

func NewRunner(stats *Stats) (*Runner, error) {
	cache, err := cache.Default()
	if err != nil {
		return nil, err
	}

	return &Runner{
		cache: cache,
		stats: stats,
	}, nil
}

// Run loads packages corresponding to patterns and analyses them with
// analyzers. It returns the loaded packages, which contain reported
// diagnostics as well as extracted ignore directives.
//
// Note that diagnostics have not been filtered at this point yet, to
// accomodate cumulative analyzes that require additional steps to
// produce diagnostics.
func (r *Runner) Run(cfg *packages.Config, patterns []string, analyzers []*analysis.Analyzer, hasCumulative bool) ([]*Package, error) {
	r.analyzerIDs = analyzerIDs{m: map[*analysis.Analyzer]int{}}
	id := 0
	seen := map[*analysis.Analyzer]struct{}{}
	var dfs func(a *analysis.Analyzer)
	dfs = func(a *analysis.Analyzer) {
		if _, ok := seen[a]; ok {
			return
		}
		seen[a] = struct{}{}
		r.analyzerIDs.m[a] = id
		id++
		for _, f := range a.FactTypes {
			gob.Register(f)
		}
		for _, req := range a.Requires {
			dfs(req)
		}
	}
	for _, a := range analyzers {
		if v := a.Flags.Lookup("go"); v != nil {
			v.Value.Set(fmt.Sprintf("1.%d", r.goVersion))
		}
		dfs(a)
	}
	for _, a := range injectedAnalyses {
		dfs(a)
	}

	var dcfg packages.Config
	if cfg != nil {
		dcfg = *cfg
	}

	atomic.StoreUint32(&r.stats.State, StateGraph)
	initialPkgs, err := r.ld.Graph(dcfg, patterns...)
	if err != nil {
		return nil, err
	}

	defer r.cache.Trim()

	var allPkgs []*Package
	m := map[*packages.Package]*Package{}
	packages.Visit(initialPkgs, nil, func(l *packages.Package) {
		m[l] = &Package{
			Package:  l,
			results:  make([]*result, len(r.analyzerIDs.m)),
			facts:    make([]map[types.Object][]analysis.Fact, len(r.analyzerIDs.m)),
			pkgFacts: make([][]analysis.Fact, len(r.analyzerIDs.m)),
			done:     make(chan struct{}),
			// every package needs itself
			dependents:    1,
			canClearTypes: !hasCumulative,
		}
		allPkgs = append(allPkgs, m[l])
		for i := range m[l].facts {
			m[l].facts[i] = map[types.Object][]analysis.Fact{}
		}
		for _, err := range l.Errors {
			m[l].errs = append(m[l].errs, err)
		}
		for _, v := range l.Imports {
			m[v].dependents++
			m[l].Imports = append(m[l].Imports, m[v])
		}

		m[l].hash, err = packageHash(m[l])
		if err != nil {
			m[l].errs = append(m[l].errs, err)
		}
	})

	pkgs := make([]*Package, len(initialPkgs))
	for i, l := range initialPkgs {
		pkgs[i] = m[l]
		pkgs[i].initial = true
	}

	atomic.StoreUint32(&r.stats.InitialPackages, uint32(len(initialPkgs)))
	atomic.StoreUint32(&r.stats.TotalPackages, uint32(len(allPkgs)))
	atomic.StoreUint32(&r.stats.State, StateProcessing)

	var wg sync.WaitGroup
	wg.Add(len(allPkgs))
	r.loadSem = make(chan struct{}, runtime.GOMAXPROCS(-1))
	atomic.StoreUint32(&r.stats.TotalWorkers, uint32(cap(r.loadSem)))
	for _, pkg := range allPkgs {
		pkg := pkg
		go func() {
			r.processPkg(pkg, analyzers)

			if pkg.initial {
				atomic.AddUint32(&r.stats.ProcessedInitialPackages, 1)
			}
			atomic.AddUint32(&r.stats.Problems, uint32(len(pkg.problems)))
			wg.Done()
		}()
	}
	wg.Wait()

	return pkgs, nil
}

var posRe = regexp.MustCompile(`^(.+?):(\d+)(?::(\d+)?)?`)

func parsePos(pos string) (token.Position, int, error) {
	if pos == "-" || pos == "" {
		return token.Position{}, 0, nil
	}
	parts := posRe.FindStringSubmatch(pos)
	if parts == nil {
		return token.Position{}, 0, fmt.Errorf("malformed position %q", pos)
	}
	file := parts[1]
	line, _ := strconv.Atoi(parts[2])
	col, _ := strconv.Atoi(parts[3])
	return token.Position{
		Filename: file,
		Line:     line,
		Column:   col,
	}, len(parts[0]), nil
}

// loadPkg loads a Go package. If the package is in the set of initial
// packages, it will be loaded from source, otherwise it will be
// loaded from export data. In the case that the package was loaded
// from export data, cached facts will also be loaded.
//
// Currently, only cached facts for this package will be loaded, not
// for any of its dependencies.
func (r *Runner) loadPkg(pkg *Package, analyzers []*analysis.Analyzer) error {
	if pkg.Types != nil {
		panic(fmt.Sprintf("internal error: %s has already been loaded", pkg.Package))
	}

	// Load type information
	if pkg.initial {
		// Load package from source
		pkg.fromSource = true
		return r.ld.LoadFromSource(pkg.Package)
	}

	// Load package from export data
	if err := r.ld.LoadFromExport(pkg.Package); err != nil {
		// We asked Go to give us up to date export data, yet
		// we can't load it. There must be something wrong.
		//
		// Attempt loading from source. This should fail (because
		// otherwise there would be export data); we just want to
		// get the compile errors. If loading from source succeeds
		// we discard the result, anyway. Otherwise we'll fail
		// when trying to reload from export data later.
		//
		// FIXME(dh): we no longer reload from export data, so
		// theoretically we should be able to continue
		pkg.fromSource = true
		if err := r.ld.LoadFromSource(pkg.Package); err != nil {
			return err
		}
		// Make sure this package can't be imported successfully
		pkg.Package.Errors = append(pkg.Package.Errors, packages.Error{
			Pos:  "-",
			Msg:  fmt.Sprintf("could not load export data: %s", err),
			Kind: packages.ParseError,
		})
		return fmt.Errorf("could not load export data: %s", err)
	}

	failed := false
	seen := make([]bool, len(r.analyzerIDs.m))
	var dfs func(*analysis.Analyzer)
	dfs = func(a *analysis.Analyzer) {
		if seen[r.analyzerIDs.get(a)] {
			return
		}
		seen[r.analyzerIDs.get(a)] = true

		if len(a.FactTypes) > 0 {
			facts, ok := r.loadCachedFacts(a, pkg)
			if !ok {
				failed = true
				return
			}

			for _, f := range facts {
				if f.Path == "" {
					// This is a package fact
					pkg.pkgFacts[r.analyzerIDs.get(a)] = append(pkg.pkgFacts[r.analyzerIDs.get(a)], f.Fact)
					continue
				}
				obj, err := objectpath.Object(pkg.Types, objectpath.Path(f.Path))
				if err != nil {
					// Be lenient about these errors. For example, when
					// analysing io/ioutil from source, we may get a fact
					// for methods on the devNull type, and objectpath
					// will happily create a path for them. However, when
					// we later load io/ioutil from export data, the path
					// no longer resolves.
					//
					// If an exported type embeds the unexported type,
					// then (part of) the unexported type will become part
					// of the type information and our path will resolve
					// again.
					continue
				}
				pkg.facts[r.analyzerIDs.get(a)][obj] = append(pkg.facts[r.analyzerIDs.get(a)][obj], f.Fact)
			}
		}

		for _, req := range a.Requires {
			dfs(req)
		}
	}
	for _, a := range analyzers {
		dfs(a)
	}

	if failed {
		pkg.fromSource = true
		// XXX we added facts to the maps, we need to get rid of those
		return r.ld.LoadFromSource(pkg.Package)
	}

	return nil
}

type analysisError struct {
	analyzer *analysis.Analyzer
	pkg      *Package
	err      error
}

func (err analysisError) Error() string {
	return fmt.Sprintf("error running analyzer %s on %s: %s", err.analyzer, err.pkg, err.err)
}

// processPkg processes a package. This involves loading the package,
// either from export data or from source. For packages loaded from
// source, the provides analyzers will be run on the package.
func (r *Runner) processPkg(pkg *Package, analyzers []*analysis.Analyzer) {
	defer func() {
		// Clear information we no longer need. Make sure to do this
		// when returning from processPkg so that we clear
		// dependencies, not just initial packages.
		pkg.TypesInfo = nil
		pkg.Syntax = nil
		pkg.results = nil

		atomic.AddUint32(&r.stats.ProcessedPackages, 1)
		pkg.decUse()
		close(pkg.done)
	}()

	// Ensure all packages have the generated map and config. This is
	// required by interna of the runner. Analyses that themselves
	// make use of either have an explicit dependency so that other
	// runners work correctly, too.
	analyzers = append(analyzers[0:len(analyzers):len(analyzers)], injectedAnalyses...)

	if len(pkg.errs) != 0 {
		return
	}

	for _, imp := range pkg.Imports {
		<-imp.done
		if len(imp.errs) > 0 {
			if imp.initial {
				// Don't print the error of the dependency since it's
				// an initial package and we're already printing the
				// error.
				pkg.errs = append(pkg.errs, fmt.Errorf("could not analyze dependency %s of %s", imp, pkg))
			} else {
				var s string
				for _, err := range imp.errs {
					s += "\n\t" + err.Error()
				}
				pkg.errs = append(pkg.errs, fmt.Errorf("could not analyze dependency %s of %s: %s", imp, pkg, s))
			}
			return
		}
	}
	if pkg.PkgPath == "unsafe" {
		pkg.Types = types.Unsafe
		return
	}

	r.loadSem <- struct{}{}
	atomic.AddUint32(&r.stats.ActiveWorkers, 1)
	defer func() {
		<-r.loadSem
		atomic.AddUint32(&r.stats.ActiveWorkers, ^uint32(0))
	}()
	if err := r.loadPkg(pkg, analyzers); err != nil {
		pkg.errs = append(pkg.errs, err)
		return
	}

	// A package's object facts is the union of all of its dependencies.
	for _, imp := range pkg.Imports {
		for ai, m := range imp.facts {
			for obj, facts := range m {
				pkg.facts[ai][obj] = facts[0:len(facts):len(facts)]
			}
		}
	}

	if !pkg.fromSource {
		// Nothing left to do for the package.
		return
	}

	// Run analyses on initial packages and those missing facts
	var wg sync.WaitGroup
	wg.Add(len(analyzers))
	errs := make([]error, len(analyzers))
	var acs []*analysisAction
	for i, a := range analyzers {
		i := i
		a := a
		ac := r.makeAnalysisAction(a, pkg)
		acs = append(acs, ac)
		go func() {
			defer wg.Done()
			// Only initial packages and packages with missing
			// facts will have been loaded from source.
			if pkg.initial || r.hasFacts(a) {
				if _, err := r.runAnalysis(ac); err != nil {
					errs[i] = analysisError{a, pkg, err}
					return
				}
			}
		}()
	}
	wg.Wait()

	depErrors := map[dependencyError]int{}
	for _, err := range errs {
		if err == nil {
			continue
		}
		switch err := err.(type) {
		case analysisError:
			switch err := err.err.(type) {
			case dependencyError:
				depErrors[err.nested()]++
			default:
				pkg.errs = append(pkg.errs, err)
			}
		default:
			pkg.errs = append(pkg.errs, err)
		}
	}
	for err, count := range depErrors {
		pkg.errs = append(pkg.errs,
			fmt.Errorf("could not run %s@%s, preventing %d analyzers from running: %s", err.dep, pkg, count, err.err))
	}

	// We can't process ignores at this point because `unused` needs
	// to see more than one package to make its decision.
	ignores, problems := parseDirectives(pkg.Package)
	pkg.ignores = append(pkg.ignores, ignores...)
	pkg.problems = append(pkg.problems, problems...)
	for _, ac := range acs {
		pkg.problems = append(pkg.problems, ac.problems...)
	}

	if pkg.initial {
		// Only initial packages have these analyzers run, and only
		// initial packages need these.
		if pkg.results[r.analyzerIDs.get(config.Analyzer)].v != nil {
			pkg.cfg = pkg.results[r.analyzerIDs.get(config.Analyzer)].v.(*config.Config)
		}
		pkg.gen = pkg.results[r.analyzerIDs.get(facts.Generated)].v.(map[string]facts.Generator)
	}

	// In a previous version of the code, we would throw away all type
	// information and reload it from export data. That was
	// nonsensical. The *types.Package doesn't keep any information
	// live that export data wouldn't also. We only need to discard
	// the AST and the TypesInfo maps; that happens after we return
	// from processPkg.
}

// hasFacts reports whether an analysis exports any facts. An analysis
// that has a transitive dependency that exports facts is considered
// to be exporting facts.
func (r *Runner) hasFacts(a *analysis.Analyzer) bool {
	ret := false
	seen := make([]bool, len(r.analyzerIDs.m))
	var dfs func(*analysis.Analyzer)
	dfs = func(a *analysis.Analyzer) {
		if seen[r.analyzerIDs.get(a)] {
			return
		}
		seen[r.analyzerIDs.get(a)] = true
		if len(a.FactTypes) > 0 {
			ret = true
		}
		for _, req := range a.Requires {
			if ret {
				break
			}
			dfs(req)
		}
	}
	dfs(a)
	return ret
}

func parseDirective(s string) (cmd string, args []string) {
	if !strings.HasPrefix(s, "//lint:") {
		return "", nil
	}
	s = strings.TrimPrefix(s, "//lint:")
	fields := strings.Split(s, " ")
	return fields[0], fields[1:]
}

// parseDirectives extracts all linter directives from the source
// files of the package. Malformed directives are returned as problems.
func parseDirectives(pkg *packages.Package) ([]Ignore, []Problem) {
	var ignores []Ignore
	var problems []Problem

	for _, f := range pkg.Syntax {
		found := false
	commentLoop:
		for _, cg := range f.Comments {
			for _, c := range cg.List {
				if strings.Contains(c.Text, "//lint:") {
					found = true
					break commentLoop
				}
			}
		}
		if !found {
			continue
		}
		cm := ast.NewCommentMap(pkg.Fset, f, f.Comments)
		for node, cgs := range cm {
			for _, cg := range cgs {
				for _, c := range cg.List {
					if !strings.HasPrefix(c.Text, "//lint:") {
						continue
					}
					cmd, args := parseDirective(c.Text)
					switch cmd {
					case "ignore", "file-ignore":
						if len(args) < 2 {
							p := Problem{
								Pos:      DisplayPosition(pkg.Fset, c.Pos()),
								Message:  "malformed linter directive; missing the required reason field?",
								Severity: Error,
								Check:    "compile",
							}
							problems = append(problems, p)
							continue
						}
					default:
						// unknown directive, ignore
						continue
					}
					checks := strings.Split(args[0], ",")
					pos := DisplayPosition(pkg.Fset, node.Pos())
					var ig Ignore
					switch cmd {
					case "ignore":
						ig = &LineIgnore{
							File:   pos.Filename,
							Line:   pos.Line,
							Checks: checks,
							Pos:    c.Pos(),
						}
					case "file-ignore":
						ig = &FileIgnore{
							File:   pos.Filename,
							Checks: checks,
						}
					}
					ignores = append(ignores, ig)
				}
			}
		}
	}

	return ignores, problems
}

// packageHash computes a package's hash. The hash is based on all Go
// files that make up the package, as well as the hashes of imported
// packages.
func packageHash(pkg *Package) (string, error) {
	key := cache.NewHash("package hash")
	fmt.Fprintf(key, "pkgpath %s\n", pkg.PkgPath)
	for _, f := range pkg.CompiledGoFiles {
		h, err := cache.FileHash(f)
		if err != nil {
			return "", err
		}
		fmt.Fprintf(key, "file %s %x\n", f, h)
	}

	imps := make([]*Package, len(pkg.Imports))
	copy(imps, pkg.Imports)
	sort.Slice(imps, func(i, j int) bool {
		return imps[i].PkgPath < imps[j].PkgPath
	})
	for _, dep := range imps {
		if dep.PkgPath == "unsafe" {
			continue
		}

		fmt.Fprintf(key, "import %s %s\n", dep.PkgPath, dep.hash)
	}
	h := key.Sum()
	return hex.EncodeToString(h[:]), nil
}

// passActionID computes an ActionID for an analysis pass.
func passActionID(pkg *Package, analyzer *analysis.Analyzer) (cache.ActionID, error) {
	key := cache.NewHash("action ID")
	fmt.Fprintf(key, "pkgpath %s\n", pkg.PkgPath)
	fmt.Fprintf(key, "pkghash %s\n", pkg.hash)
	fmt.Fprintf(key, "analyzer %s\n", analyzer.Name)

	return key.Sum(), nil
}