Improves package analysis errors usability (fanal#24)

- Adds a new analyzer error for "no packages detected"
- Package analyzers now return the common "no packages detected" error
- Returned errors from the package analyzers are checked against the
  common "no packages detected" errors and filters those out. Other
  errors will now be passed back to the user for debugging.

Author: ahamilton55

analyzer/analyzer.go

@@ -25,6 +25,8 @@ var (
 	ErrUnknownOS = xerrors.New("Unknown OS")
 	// ErrPkgAnalysis occurs when the analysis of packages is failed.
 	ErrPkgAnalysis = xerrors.New("Failed to analyze packages")
+	// ErrNoPkgsDetected occurs when the required files for an OS package manager are not detected
+	ErrNoPkgsDetected = xerrors.New("No packages detected")
 )
 
 type OSAnalyzer interface {
@@ -158,10 +160,12 @@ func GetOS(filesMap extractor.FileMap) (OS, error) {
 func GetPackages(filesMap extractor.FileMap) ([]Package, error) {
 	for _, analyzer := range pkgAnalyzers {
 		pkgs, err := analyzer.Analyze(filesMap)
-		if err != nil {
+
+		// Differentiate between a package manager not being found and another error
+		if err != nil && err == ErrNoPkgsDetected {
 			continue
 		}
-		return pkgs, nil
+		return pkgs, err
 	}
 	return nil, ErrPkgAnalysis
 }

analyzer/pkg/apk/apk.go

@@ -5,8 +5,6 @@ import (
 	"bytes"
 	"log"
 
-	"github.com/pkg/errors"
-
 	"github.com/knqyf263/fanal/analyzer"
 	"github.com/knqyf263/fanal/extractor"
 
@@ -33,7 +31,7 @@ func (a alpinePkgAnalyzer) Analyze(fileMap extractor.FileMap) (pkgs []analyzer.P
 		detected = true
 	}
 	if !detected {
-		return pkgs, errors.New("No package detected")
+		return pkgs, analyzer.ErrNoPkgsDetected
 	}
 	return pkgs, nil
 }

analyzer/pkg/dpkg/dpkg.go

@@ -8,7 +8,6 @@ import (
 	"strings"
 
 	mapset "github.com/deckarep/golang-set"
-	"golang.org/x/xerrors"
 
 	"github.com/knqyf263/fanal/analyzer"
 	"github.com/knqyf263/fanal/extractor"
@@ -39,7 +38,7 @@ func (a debianPkgAnalyzer) Analyze(fileMap extractor.FileMap) (pkgs []analyzer.P
 		detected = true
 	}
 	if !detected {
-		return pkgs, xerrors.New("no package detected")
+		return pkgs, analyzer.ErrNoPkgsDetected
 	}
 	return pkgs, nil
 }

analyzer/pkg/rpm/rpm.go

@@ -5,8 +5,6 @@ import (
 	"os"
 	"path/filepath"
 
-	"golang.org/x/xerrors"
-
 	"github.com/knqyf263/fanal/analyzer"
 	"github.com/knqyf263/fanal/extractor"
 	rpmdb "github.com/knqyf263/go-rpmdb/pkg"
@@ -31,7 +29,7 @@ func (a rpmPkgAnalyzer) Analyze(fileMap extractor.FileMap) (pkgs []analyzer.Pack
 		detected = true
 	}
 	if !detected {
-		return nil, xerrors.New("No package detected")
+		return nil, analyzer.ErrNoPkgsDetected
 	}
 	return pkgs, err
 }

analyzer/pkg/rpmcmd/rpm.go

@@ -2,7 +2,6 @@ package rpmcmd
 
 import (
 	"bufio"
-	"errors"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -35,7 +34,7 @@ func (a rpmCmdPkgAnalyzer) Analyze(fileMap extractor.FileMap) (pkgs []analyzer.P
 		detected = true
 	}
 	if !detected {
-		return pkgs, errors.New("No package detected")
+		return pkgs, analyzer.ErrNoPkgsDetected
 	}
 	return pkgs, err
 }