facts.go

package analyzer_wrapper

import (
	"bytes"
	"encoding/gob"
	"fmt"
	"golang.org/x/tools/go/analysis"
	"log"
	"reflect"
)

func factType(fact analysis.Fact) reflect.Type {
	t := reflect.TypeOf(fact)
	if t.Kind() != reflect.Ptr {
		log.Fatalf("invalid Fact type: got %T, want pointer", fact)
	}
	return t
}

// inheritFacts populates act.facts with
// those it obtains from its dependency, dep.
func inheritFacts(act, dep *action) {
	for key, fact := range dep.objectFacts {
		// Filter out facts related to objects
		// that are irrelevant downstream
		// (equivalently: not in the compiler export data).
		if !exportedFrom(key.obj, dep.pkg.Types) {
			if false {
				log.Printf("%v: discarding %T fact from %s for %s: %s", act, fact, dep, key.obj, fact)
			}
			continue
		}

		act.objectFacts[key] = fact
	}

	for key, fact := range dep.packageFacts {
		// TODO: filter out facts that belong to
		// packages not mentioned in the export data
		// to prevent side channels.
		act.packageFacts[key] = fact
	}
}

// codeFact encodes then decodes a fact,
// just to exercise that logic.
func codeFact(fact analysis.Fact) (analysis.Fact, error) {
	// We encode facts one at a time.
	// A real modular driver would emit all facts
	// into one encoder to improve gob efficiency.
	var buf bytes.Buffer
	if err := gob.NewEncoder(&buf).Encode(fact); err != nil {
		return nil, err
	}

	// Encode it twice and assert that we get the same bits.
	// This helps detect nondeterministic Gob encoding (e.g. of maps).
	var buf2 bytes.Buffer
	if err := gob.NewEncoder(&buf2).Encode(fact); err != nil {
		return nil, err
	}
	if !bytes.Equal(buf.Bytes(), buf2.Bytes()) {
		return nil, fmt.Errorf("encoding of %T fact is nondeterministic", fact)
	}

	new := reflect.New(reflect.TypeOf(fact).Elem()).Interface().(analysis.Fact)
	if err := gob.NewDecoder(&buf).Decode(new); err != nil {
		return nil, err
	}
	return new, nil
}

// needFacts reports whether any analysis required by the specified set
// needs facts.  If so, we must load the entire program from source.
func needFacts(analyzers []*analysis.Analyzer) bool {
	seen := make(map[*analysis.Analyzer]bool)
	var q []*analysis.Analyzer // for BFS
	q = append(q, analyzers...)
	for len(q) > 0 {
		a := q[0]
		q = q[1:]
		if !seen[a] {
			seen[a] = true
			if len(a.FactTypes) > 0 {
				return true
			}
			q = append(q, a.Requires...)
		}
	}
	return false
}