pkg/tool/exec: add a Run.mustSucceed parameter

Currently, exec.Run results in a fatal error if the command returns
a non-zero exit status, meaning that the "success" field can only ever
be used by other CUE expressions when it is set to true.

Add a mustSucceed boolean parameter, defaulting to true to keep the
default behavior fully backwards compatible.
When set to false, exec errors will allow "cue cmd" to continue
with the "success" field set to false.

Fixes #2632.

Closes #2702 as merged as of commit a454651.

Signed-off-by: Nick Figgins <[email protected]>
Co-authored-by: Daniel Martí <[email protected]>
Change-Id: If52e16549dddfbc74db514cd562cf9fefc26f9f0
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1172991
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: nickfiggins

cmd/cue/cmd/testdata/script/cmd_execerr.txtar

@@ -0,0 +1,56 @@
+! exec cue cmd cannotFail
+cmp stderr cannotFail-stderr.golden
+
+exec cue cmd canFail
+cmp stdout canFail-stdout.golden
+
+-- cue.mod/module.cue --
+module: "example.com"
+
+-- cannotFail-stderr.golden --
+task failed: command "false" failed: exit status 1
+-- canFail-stdout.golden --
+errExit:
+success=false
+hasStderr=false
+
+errNotFound:
+success=false
+hasStderr=true
+-- foo_tool.cue --
+package foo
+
+import (
+	"tool/cli"
+	"tool/exec"
+)
+
+command: cannotFail: {
+	one: exec.Run & {
+		cmd: ["false"]
+	}
+}
+
+command: canFail: {
+	errExit: exec.Run & {
+		cmd: ["false"]
+		stderr: string
+		mustSucceed: false
+	}
+	errNotFound: exec.Run & {
+		cmd: ["program-does-not-exist"]
+		stderr: string
+		mustSucceed: false
+	}
+	second: cli.Print & {
+		text: """
+			errExit:
+			success=\(errExit.success)
+			hasStderr=\(errExit.stderr != "")
+
+			errNotFound:
+			success=\(errNotFound.success)
+			hasStderr=\(errNotFound.stderr != "")
+			"""
+	}
+}

pkg/tool/exec/exec.cue

@@ -48,4 +48,8 @@ Run: {
 	// code or false otherwise. The user can explicitly specify the value
 	// force a fatal error if the desired success code is not reached.
 	success: bool
+
+	// mustSucceed indicates whether a command must succeed, in which case success==false results in a fatal error.
+	// This option is enabled by default, but may be disabled to control what is done when a command execution fails.
+	mustSucceed: bool | *true
 }

pkg/tool/exec/exec.go

@@ -71,6 +71,16 @@ func (c *execCmd) Run(ctx *task.Context) (res interface{}, err error) {
 		cmd.Stderr = ctx.Stderr
 	}
 
+	// TODO(mvdan): exec.Run declares mustSucceed as a regular field with a default of true.
+	// We should be able to rely on that here, removing the need for Exists and repeating the default.
+	mustSucceed := true
+	if v := ctx.Obj.LookupPath(cue.ParsePath("mustSucceed")); v.Exists() {
+		mustSucceed, err = v.Bool()
+		if err != nil {
+			return nil, errors.Wrapf(err, v.Pos(), "invalid bool value")
+		}
+	}
+
 	update := map[string]interface{}{}
 	if captureOut {
 		var stdout []byte
@@ -80,15 +90,23 @@ func (c *execCmd) Run(ctx *task.Context) (res interface{}, err error) {
 		err = cmd.Run()
 	}
 	update["success"] = err == nil
-	if err != nil {
-		if exit := (*exec.ExitError)(nil); errors.As(err, &exit) && captureErr {
+
+	if err == nil {
+		return update, nil
+	}
+
+	if captureErr {
+		if exit := (*exec.ExitError)(nil); errors.As(err, &exit) {
 			update["stderr"] = string(exit.Stderr)
 		} else {
-			update = nil
+			update["stderr"] = err.Error()
 		}
-		err = fmt.Errorf("command %q failed: %v", doc, err)
 	}
-	return update, err
+	if !mustSucceed {
+		return update, nil
+	}
+
+	return nil, fmt.Errorf("command %q failed: %v", doc, err)
 }
 
 func mkCommand(ctx *task.Context) (c *exec.Cmd, doc string, err error) {

pkg/tool/exec/pkg.go

@@ -48,14 +48,14 @@ graph TD
 }
 -- out/run/t1/stats --
 Leaks:  0
-Freed:  42
-Reused: 35
+Freed:  45
+Reused: 38
 Allocs: 7
 Retain: 0
 
-Unifications: 25
-Conjuncts:    65
-Disjuncts:    42
+Unifications: 26
+Conjuncts:    68
+Disjuncts:    45
 -- out/run/t2 --
 graph TD
   t0("root.get [Terminated]")
@@ -67,10 +67,11 @@ graph TD
 	$id: "tool/exec.Run"
 	cmd: "go run cuelang.org/go/cmd/cue import -f -p json -l #Workflow: jsonschema: - --outfile pkg/github.com/SchemaStore/schemastore/src/schemas/json/github-workflow.cue"
 	env: {}
-	stdout:  "foo"
-	stderr:  null
-	stdin:   (*null | string | bytes) & GET.response.body
-	success: bool
+	stdout:      "foo"
+	stderr:      null
+	stdin:       (*null | string | bytes) & GET.response.body
+	success:     bool
+	mustSucceed: true
 
 	//cue:path: root.get
 	let GET = {
@@ -90,24 +91,24 @@ graph TD
 }
 -- out/run/t2/stats --
 Leaks:  0
-Freed:  42
-Reused: 42
+Freed:  45
+Reused: 45
 Allocs: 0
 Retain: 0
 
-Unifications: 25
-Conjuncts:    69
-Disjuncts:    42
+Unifications: 26
+Conjuncts:    72
+Disjuncts:    45
 -- out/run/stats/totals --
 Leaks:  0
-Freed:  84
-Reused: 77
+Freed:  90
+Reused: 83
 Allocs: 7
 Retain: 0
 
-Unifications: 50
-Conjuncts:    134
-Disjuncts:    84
+Unifications: 52
+Conjuncts:    140
+Disjuncts:    90
 -- out/run/t3 --
 graph TD
   t0("root.get [Terminated]")