build: add more methods to invoke cpp

Add an environment variable and CLI flag to force the use of the C
Preprocessor (cpp) instead of only relying on the Containerfile suffix.

Closes #6744

Signed-off-by: James Harmison <jharmison@gmail.com>

Author: solacelost

define/build.go

@@ -265,6 +265,8 @@ type BuildOptions struct {
 	CommonBuildOpts *CommonBuildOptions
 	// CPPFlags are additional arguments to pass to the C Preprocessor (cpp).
 	CPPFlags []string
+	// Preprocess tells the builder to run the C Preprocessor (cpp) regardless of the file extension.
+	Preprocess types.OptionalBool
 	// DefaultMountsFilePath is the file path holding the mounts to be mounted for RUN
 	// instructions in "host-path:container-path" format
 	DefaultMountsFilePath string

docs/buildah-build.1.md

@@ -18,7 +18,7 @@ The build context directory can be specified as the http(s) URL of an archive, g
 
 If no context directory is specified, then Buildah will assume the current working directory as build context, which should contain a Containerfile.
 
-Containerfiles ending with a ".in" suffix will be preprocessed via cpp(1).  This can be useful to decompose Containerfiles into several reusable parts that can be used via CPP's **#include** directive.  Notice, a Containerfile.in file can still be used by other tools when manually preprocessing them via `cpp -E`. Any comments ( Lines beginning with `#` ) in included Containerfile(s) that are not preprocess commands, will be printed as warnings during builds.
+Containerfiles ending with a ".in" suffix will be automatically preprocessed via cpp(1).  This can be useful to decompose Containerfiles into several reusable parts that can be used via CPP's **#include** directive.  Notice, a Containerfile.in file can still be used by other tools when manually preprocessing them via `cpp -E`. Any comments ( Lines beginning with `#` ) in included Containerfile(s) that are not preprocess commands, will be printed as warnings during builds.
 
 When the URL is an archive, the contents of the URL is downloaded to a temporary location and extracted before execution.
 
@@ -820,6 +820,13 @@ The `buildah build` command allows building images for all Linux architectures,
 
 **NOTE:** The `--platform` option may not be used in combination with the `--arch`, `--os`, or `--variant` options.
 
+**--preprocess**
+
+If specified, will always attempt to use the C Preprocessor cpp(1),
+even if the Containerfile doesn't end with the ".in" suffix.
+Note: You can also configure this behavior by setting the BUILDAH\_PREPROCESS
+environment variable to `1`, `true`, or `yes`.
+
 **--pull**
 
 Pull image policy. If not specified, the default is **missing**. If an explicit

imagebuildah/build.go

@@ -162,8 +162,10 @@ func BuildDockerfiles(ctx context.Context, store storage.Store, options define.B
 			data = contents
 		}
 
-		// pre-process Dockerfiles with ".in" suffix
-		if strings.HasSuffix(dfile, ".in") {
+		// pre-process Dockerfiles with ".in" suffix, if --preprocess is specified, or if BUILDAH_PREPROCESS is set
+		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,
@@ -397,6 +400,7 @@ func GenBuildOptions(c *cobra.Command, inputArgs []string, iopts BuildOptions) (
 		CompatVolumes:           compatVolumes,
 		ConfidentialWorkload:    confidentialWorkloadOptions,
 		CPPFlags:                iopts.CPPFlags,
+		Preprocess:              preprocess,
 		CommonBuildOpts:         commonOpts,
 		Compression:             compression,
 		ConfigureNetwork:        networkPolicy,

pkg/cli/common.go

@@ -70,6 +70,7 @@ type BudResults struct {
 	Compress            bool
 	Creds               string
 	CPPFlags            []string
+	Preprocess          bool
 	DisableCompression  bool
 	DisableContentTrust bool
 	IgnoreFile          string
@@ -247,6 +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", 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`")
@@ -536,6 +538,16 @@ func DefaultHistory() bool {
 	return false
 }
 
+// DefaultPreprocess returns true if BUILDAH_PREPROCESS is set to "1" or "true"
+// otherwise it returns false
+func DefaultPreprocess() bool {
+	preprocess := os.Getenv("BUILDAH_PREPROCESS")
+	if strings.ToLower(preprocess) == "true" || preprocess == "1" {
+		return true
+	}
+	return false
+}
+
 func VerifyFlagsArgsOrder(args []string) error {
 	for _, arg := range args {
 		if strings.HasPrefix(arg, "-") {

tests/bud.bats

@@ -4101,6 +4101,46 @@ _EOF
   expect_output --substring "Ignoring <stdin>:5:2: error: #error"
 }
 
+@test "bud with preprocessor, via --preprocess" {
+  _prefetch busybox
+  target=alpine-image
+  run_buildah build $WITH_POLICY_JSON -t ${target} --preprocess -f Decomposed.tpl $BUDFILES/preprocess
+}
+
+@test "bud with preprocessor-requiring containerfile, without --preprocess" {
+  _prefetch busybox
+  target=alpine-image
+  run_buildah 125 build $WITH_POLICY_JSON -t ${target} -f Decomposed.tpl $BUDFILES/preprocess
+  expect_output --substring 'Build error: Unknown instruction: "RUNHELLO"'
+}
+
+@test "bud with preprocessor error, via --preprocess" {
+  _prefetch busybox
+  target=alpine-image
+  run_buildah bud $WITH_POLICY_JSON -t ${target} --preprocess -f Error.tpl $BUDFILES/preprocess
+  expect_output --substring "Ignoring <stdin>:5:2: error: #error"
+}
+
+@test "bud with preprocessor, via env var" {
+  _prefetch busybox
+  target=alpine-image
+  BUILDAH_PREPROCESS=1 run_buildah build $WITH_POLICY_JSON -t ${target} -f Decomposed.tpl $BUDFILES/preprocess
+}
+
+@test "bud with preprocessor error, via env var" {
+  _prefetch busybox
+  target=alpine-image
+  BUILDAH_PREPROCESS=1 run_buildah bud $WITH_POLICY_JSON -t ${target} -f Error.tpl $BUDFILES/preprocess
+  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

tests/bud/preprocess/Decomposed.tpl

@@ -0,0 +1,5 @@
+FROM busybox
+
+#include "common"
+
+RUNHELLO

tests/bud/preprocess/Error.tpl

@@ -0,0 +1,5 @@
+FROM busybox
+
+#include "common"
+
+#error THISERROR