Restore build args after optimize. Fixes #1910, #1912. (#1915)

* Restore build args after optimize. Fixes #1910, #1912.

* Apply review suggestions.

pkg/dockerfile/buildargs.go

@@ -51,8 +51,11 @@ func (b *BuildArgs) Clone() *BuildArgs {
 
 // ReplacementEnvs returns a list of filtered environment variables
 func (b *BuildArgs) ReplacementEnvs(envs []string) []string {
+	// Ensure that we operate on a new array and do not modify the underlying array
+	resultEnv := make([]string, len(envs))
+	copy(resultEnv, envs)
 	filtered := b.FilterAllowed(envs)
-	return append(envs, filtered...)
+	return append(resultEnv, filtered...)
 }
 
 // AddMetaArgs adds the supplied args map to b's allowedMetaArgs

pkg/executor/build.go

@@ -21,6 +21,7 @@ import (
 	"os"
 	"path/filepath"
 	"runtime"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -181,6 +182,9 @@ func initConfig(img partial.WithConfigFile, opts *config.KanikoOptions) (*v1.Con
 func (s *stageBuilder) populateCompositeKey(command fmt.Stringer, files []string, compositeKey CompositeCache, args *dockerfile.BuildArgs, env []string) (CompositeCache, error) {
 	// First replace all the environment variables or args in the command
 	replacementEnvs := args.ReplacementEnvs(env)
+	// The sort order of `replacementEnvs` is basically undefined, sort it
+	// so we can ensure a stable cache key.
+	sort.Strings(replacementEnvs)
 	resolvedCmd, err := util.ResolveEnvironmentReplacement(command.String(), replacementEnvs, false)
 	if err != nil {
 		return compositeKey, err
@@ -227,6 +231,11 @@ func (s *stageBuilder) optimize(compositeKey CompositeCache, cfg v1.Config) erro
 	if !s.opts.Cache {
 		return nil
 	}
+	var buildArgs = s.args.Clone()
+	// Restore build args back to their original values
+	defer func() {
+		s.args = buildArgs
+	}()
 
 	stopCache := false
 	// Possibly replace commands with their cached implementations.