fix: use BUILDAH_PREPROCESS only to change default

explicitly disabling preprocessing requires using --preprocess=false kwarg

Author: solacelost

imagebuildah/build.go

@@ -163,7 +163,9 @@ func BuildDockerfiles(ctx context.Context, store storage.Store, options define.B
 		}
 
 		// pre-process Dockerfiles with ".in" suffix, if --preprocess is specified, or if BUILDAH_PREPROCESS is set
-		if strings.HasSuffix(dfile, ".in") || options.Preprocess {
+		preprocessSpecified := options.Preprocess == types.OptionalBoolTrue
+		preprocessInferred := (options.Preprocess == types.OptionalBoolUndefined) && strings.HasSuffix(dfile, ".in")
+		if preprocessSpecified || preprocessInferred {
 			pData, err := preprocessContainerfileContents(logger, dfile, data, options.ContextDirectory, options.CPPFlags)
 			if err != nil {
 				return "", nil, err

pkg/cli/build.go

@@ -363,7 +363,7 @@ func GenBuildOptions(c *cobra.Command, inputArgs []string, iopts BuildOptions) (
 		sbomScanOptions = append(sbomScanOptions, *sbomScanOption)
 	}
 
-	var compatVolumes, createdAnnotation, inheritAnnotations, inheritLabels, skipUnusedStages types.OptionalBool
+	var compatVolumes, createdAnnotation, inheritAnnotations, inheritLabels, skipUnusedStages, preprocess types.OptionalBool
 	if c.Flag("compat-volumes").Changed {
 		compatVolumes = types.NewOptionalBool(iopts.CompatVolumes)
 	}
@@ -379,6 +379,9 @@ func GenBuildOptions(c *cobra.Command, inputArgs []string, iopts BuildOptions) (
 	if c.Flag("skip-unused-stages").Changed {
 		skipUnusedStages = types.NewOptionalBool(iopts.SkipUnusedStages)
 	}
+	if c.Flag("preprocess").Changed || DefaultPreprocess() {
+		preprocess = types.NewOptionalBool(iopts.Preprocess)
+	}
 
 	options = define.BuildOptions{
 		AddCapabilities:         iopts.CapAdd,
@@ -397,7 +400,7 @@ func GenBuildOptions(c *cobra.Command, inputArgs []string, iopts BuildOptions) (
 		CompatVolumes:           compatVolumes,
 		ConfidentialWorkload:    confidentialWorkloadOptions,
 		CPPFlags:                iopts.CPPFlags,
-		Preprocess:              iopts.Preprocess,
+		Preprocess:              preprocess,
 		CommonBuildOpts:         commonOpts,
 		Compression:             compression,
 		ConfigureNetwork:        networkPolicy,

pkg/cli/common.go

@@ -248,7 +248,7 @@ func GetBudFlags(flags *BudResults) pflag.FlagSet {
 	fs.BoolVar(&flags.InheritLabels, "inherit-labels", true, "inherit the labels from the base image or base stages.")
 	fs.BoolVar(&flags.InheritAnnotations, "inherit-annotations", true, "inherit the annotations from the base image or base stages.")
 	fs.StringArrayVar(&flags.CPPFlags, "cpp-flag", []string{}, "set additional flag to pass to C preprocessor (cpp)")
-	fs.BoolVar(&flags.Preprocess, "preprocess", PreprocessContainerfile(), "use the C preprocessor (cpp) on a Dockerfile, regardless of the file suffix")
+	fs.BoolVar(&flags.Preprocess, "preprocess", DefaultPreprocess(), "use the C preprocessor (cpp) on a Dockerfile, regardless of the file suffix. Use BUILDAH_PREPROCESS environment variable to change default.")
 	fs.BoolVar(&flags.CreatedAnnotation, "created-annotation", true, `set an "org.opencontainers.image.created" annotation in the image`)
 	fs.StringVar(&flags.Creds, "creds", "", "use `[username[:password]]` for accessing the registry")
 	fs.StringVarP(&flags.CWOptions, "cw", "", "", "confidential workload `options`")
@@ -538,9 +538,9 @@ func DefaultHistory() bool {
 	return false
 }
 
-// PreprocessContainerfile returns true if BUILDAH_PREPROCESS is set to "1" or "true"
+// DefaultPreprocess returns true if BUILDAH_PREPROCESS is set to "1" or "true"
 // otherwise it returns false
-func PreprocessContainerfile() bool {
+func DefaultPreprocess() bool {
 	preprocess := os.Getenv("BUILDAH_PREPROCESS")
 	if strings.ToLower(preprocess) == "true" || preprocess == "1" {
 		return true

tests/bud.bats

@@ -4134,6 +4134,13 @@ _EOF
   expect_output --substring "Ignoring <stdin>:5:2: error: #error"
 }
 
+@test "bud with preprocessor-implied containerfile, with preprocess force disabled" {
+  _prefetch busybox
+  target=alpine-image
+  run_buildah 125 build $WITH_POLICY_JSON -t ${target} --preprocess=false -f Decomposed.in $BUDFILES/preprocess
+  expect_output --substring 'Build error: Unknown instruction: "RUNHELLO"'
+}
+
 @test "bud-with-rejected-name" {
   target=ThisNameShouldBeRejected
   run_buildah 125 build -q $WITH_POLICY_JSON -t ${target} $BUDFILES/from-scratch