cmd/entrypoint: do not interpret anything after --

The way the `flag` package works, it can eat the flag
"terminator" (aka the double dash `--`). This means that, in some very
specific cases — where the first item after the `--` is also a
subcommand, it would execute the entrypoint subcommand instead of the
actual command.

For example :

```
$ /ko-app/entrypoint -- init a b
$ /ko-app/entrypoint init a b
```

This is fixed by making sure we remove anything after `--` for the
subcommand processing. And then we pass the rest (after `--`) to the
entrypointer to be executed.

Signed-off-by: Vincent Demeester <vdemeest@redhat.com>

cmd/entrypoint/args.go

@@ -0,0 +1,38 @@
+/*
+Copyright 2022 The Tekton Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+func extractArgs(initialArgs []string) ([]string, []string) {
+	commandArgs := []string{}
+	args := initialArgs
+	if len(initialArgs) == 0 {
+		return args, commandArgs
+	}
+	// Detect if `--` is present, if it is, parse only the one before.
+	terminatorIndex := -1
+	for i, a := range initialArgs {
+		if a == "--" {
+			terminatorIndex = i
+			break
+		}
+	}
+	if terminatorIndex > 0 {
+		commandArgs = initialArgs[terminatorIndex+1:]
+		args = initialArgs[:terminatorIndex]
+	}
+	return args, commandArgs
+}

cmd/entrypoint/args_test.go

@@ -0,0 +1,67 @@
+/*
+Copyright 2022 The Tekton Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func TestExtractArgs(t *testing.T) {
+	for _, c := range []struct {
+		desc                string
+		args                []string
+		expectedArgs        []string
+		expectedCommandArgs []string
+	}{{
+		desc:                "empty arguments",
+		args:                []string{},
+		expectedArgs:        []string{},
+		expectedCommandArgs: []string{},
+	}, {
+		desc:                "with args",
+		args:                []string{"--foo", "bar", "a", "b", "c"},
+		expectedArgs:        []string{"--foo", "bar", "a", "b", "c"},
+		expectedCommandArgs: []string{},
+	}, {
+		desc:                "with terminator on its own",
+		args:                []string{"--foo", "bar", "--"},
+		expectedArgs:        []string{"--foo", "bar"},
+		expectedCommandArgs: []string{},
+	}, {
+		desc:                "with terminator",
+		args:                []string{"--foo", "bar", "--", "a", "b", "c"},
+		expectedArgs:        []string{"--foo", "bar"},
+		expectedCommandArgs: []string{"a", "b", "c"},
+	}, {
+		desc:                "with args and terminator",
+		args:                []string{"--foo", "bar", "baz", "--", "a", "b", "c"},
+		expectedArgs:        []string{"--foo", "bar", "baz"},
+		expectedCommandArgs: []string{"a", "b", "c"},
+	}} {
+		t.Run(c.desc, func(t *testing.T) {
+			args, commandArgs := extractArgs(c.args)
+			if d := cmp.Diff(c.expectedArgs, args); d != "" {
+				t.Errorf("args: diff(-want,+got):\n%s", d)
+			}
+			if d := cmp.Diff(c.expectedCommandArgs, commandArgs); d != "" {
+				t.Errorf("commandArgs: diff(-want,+got):\n%s", d)
+			}
+		})
+	}
+}

cmd/entrypoint/main.go

@@ -78,9 +78,16 @@ func main() {
 	gitcreds.AddFlags(flag.CommandLine)
 	dockercreds.AddFlags(flag.CommandLine)
 
-	flag.Parse()
-
-	if err := subcommands.Process(flag.Args()); err != nil {
+	// Split args with `--` for the entrypoint and what it should execute
+	args, commandArgs := extractArgs(os.Args[1:])
+
+	// We are using the global variable flag.CommandLine here to be able
+	// to define what args it should parse.
+	// flag.Parse() does flag.CommandLine.Parse(os.Args[1:])
+	if err := flag.CommandLine.Parse(args); err != nil {
+		os.Exit(1)
+	}
+	if err := subcommands.Process(flag.CommandLine.Args()); err != nil {
 		log.Println(err.Error())
 		switch err.(type) {
 		case subcommands.SubcommandSuccessful:
@@ -123,7 +130,7 @@ func main() {
 	}
 
 	e := entrypoint.Entrypointer{
-		Command:             append(cmd, flag.Args()...),
+		Command:             append(cmd, commandArgs...),
 		WaitFiles:           strings.Split(*waitFiles, ","),
 		WaitFileContent:     *waitFileContent,
 		PostFile:            *postFile,

examples/v1beta1/taskruns/5080-entrypoint-init-regression.yaml

@@ -0,0 +1,27 @@
+apiVersion: tekton.dev/v1beta1
+kind: TaskRun
+metadata:
+  generateName: tkn-arg-test-
+spec:
+  params:
+  - name: ARGS
+    value:
+    - init
+    - foo
+    - bar
+  taskSpec:
+    description: >-
+      Test consuming args, acts as a regression test for bug 5080
+    params:
+    - name: ARGS
+      description: The terraform cli commands to tun
+      type: array
+      default:
+      - "--help"
+    steps:
+      - name: echo-cli
+        image: registry.access.redhat.com/ubi9/ubi-minimal:9.0.0-1580
+        workingDir: /tekton/home
+        args:
+        - "$(params.ARGS)"
+        command: ["echo"]