use SYFT_LOG_FILE env var (#805)

* use SYFT_LOG_FILE

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* enable debug logs when SYFT_LOG_FILE is set

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* set log.file and add tests

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* test log file in temp directory

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* add note on binding refactor

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

* remove unused function

Signed-off-by: Jonas Galvão Xavier <jonas.agx@gmail.com>

cmd/packages.go

@@ -140,6 +140,7 @@ func setPackageFlags(flags *pflag.FlagSet) {
 	)
 }
 
+// NOTE(alex): Write a helper for the binding operation, which can be used to perform the binding but also double check that the intended effect was had or else return an error. Another thought is to somehow provide zero-valued defaults for all values in our config struct (maybe with reflection?). There may be a mechanism that already exists in viper that protects against this that I'm not aware of. ref: https://github.com/anchore/syft/pull/805#discussion_r801931192
 func bindPackagesConfigOptions(flags *pflag.FlagSet) error {
 	// Formatting & Input options //////////////////////////////////////////////
 

internal/config/logging.go

@@ -15,4 +15,5 @@ type logging struct {
 
 func (cfg logging) loadDefaultValues(v *viper.Viper) {
 	v.SetDefault("log.structured", false)
+	v.SetDefault("log.file", "")
 }

test/cli/root_cmd_test.go

@@ -1,10 +1,13 @@
 package cli
 
 import (
+	"os"
+	"path/filepath"
 	"strings"
 	"testing"
 
 	"github.com/sergi/go-diff/diffmatchpatch"
+	"github.com/stretchr/testify/assert"
 )
 
 func TestRootCmdAliasesToPackagesSubcommand(t *testing.T) {
@@ -114,3 +117,47 @@ func TestPersistentFlags(t *testing.T) {
 		})
 	}
 }
+
+func TestLogFile(t *testing.T) {
+	request := "docker-archive:" + getFixtureImage(t, "image-pkg-coverage")
+
+	envLogFile := filepath.Join(os.TempDir(), "a-pretty-log-file.log")
+	t.Logf("log file path: %s", envLogFile)
+
+	tests := []struct {
+		name       string
+		args       []string
+		env        map[string]string
+		assertions []traitAssertion
+		cleanup    func()
+	}{
+		{
+			name: "env-var-log-file-name",
+			args: []string{"-vv", request},
+			env:  map[string]string{"SYFT_LOG_FILE": envLogFile},
+			assertions: []traitAssertion{
+				func(tb testing.TB, stdout, stderr string, rc int) {
+					tb.Helper()
+					_, err := os.Stat(envLogFile)
+					assert.NoError(t, err)
+				},
+			},
+			cleanup: func() { assert.NoError(t, os.Remove(envLogFile)) },
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			t.Cleanup(test.cleanup)
+
+			cmd, stdout, stderr := runSyft(t, test.env, test.args...)
+			for _, traitFn := range test.assertions {
+				traitFn(t, stdout, stderr, cmd.ProcessState.ExitCode())
+			}
+			if t.Failed() {
+				t.Log("STDOUT:\n", stdout)
+				t.Log("STDERR:\n", stderr)
+				t.Log("COMMAND:", strings.Join(cmd.Args, " "))
+			}
+		})
+	}
+}