mcfg: Parse now takes a Context, which allows for implementing WithCLITail

mcfg/cli.go

@@ -13,6 +13,34 @@ import (
 	"github.com/mediocregopher/mediocre-go-lib/merr"
 )
 
+type cliKey int
+
+const (
+	cliKeyTailPtr cliKey = iota
+)
+
+// WithCLITail returns a Context which modifies the behavior of SourceCLI's
+// Parse, if SourceCLI is used with that Context at all. Normally when SourceCLI
+// encounters an unexpected Arg it will immediately return an error. This
+// function modifies the Context to indicate to Parse that the unexpected Arg,
+// and all subsequent Args (i.e. the tail) should be set to the returned
+// []string value.
+//
+// If multiple WithCLITail calls are used then only the latest returned pointer
+// will be filled.
+func WithCLITail(ctx context.Context) (context.Context, *[]string) {
+	tailPtr := new([]string)
+	return context.WithValue(ctx, cliKeyTailPtr, tailPtr), tailPtr
+}
+
+func populateCLITail(ctx context.Context, tail []string) bool {
+	tailPtr, ok := ctx.Value(cliKeyTailPtr).(*[]string)
+	if ok {
+		*tailPtr = tail
+	}
+	return ok
+}
+
 // SourceCLI is a Source which will parse configuration from the CLI.
 //
 // Possible CLI options are generated by joining a Param's Path and Name with
@@ -37,12 +65,6 @@ type SourceCLI struct {
 	Args []string // if nil then os.Args[1:] is used
 
 	DisableHelpPage bool
-
-	// Normally if any unexpected Arg value is encountered Parse will error out.
-	// If instead TailCallback is set then it will be called whenever the first
-	// unexpected Arg is encountered, and will not error out. TailCallback will
-	// be given a slice of Args starting at the first unexpected element.
-	TailCallback func([]string)
 }
 
 const (
@@ -53,7 +75,7 @@ const (
 )
 
 // Parse implements the method for the Source interface
-func (cli *SourceCLI) Parse(params []Param) ([]ParamValue, error) {
+func (cli *SourceCLI) Parse(ctx context.Context, params []Param) ([]ParamValue, error) {
 	args := cli.Args
 	if cli.Args == nil {
 		args = os.Args[1:]
@@ -96,8 +118,7 @@ func (cli *SourceCLI) Parse(params []Param) ([]ParamValue, error) {
 				break
 			}
 			if !pOk {
-				if cli.TailCallback != nil {
-					cli.TailCallback(args[i:])
+				if ok := populateCLITail(ctx, args[i:]); ok {
 					return pvs, nil
 				}
 				ctx := mctx.Annotate(context.Background(), "param", arg)
@@ -134,6 +155,7 @@ func (cli *SourceCLI) Parse(params []Param) ([]ParamValue, error) {
 		ctx := mctx.Annotate(p.Context, "param", key)
 		return nil, merr.New("param expected a value", ctx)
 	}
+
 	return pvs, nil
 }
 

mcfg/cli_test.go

@@ -3,6 +3,7 @@ package mcfg
 import (
 	"bytes"
 	"context"
+	"fmt"
 	"strings"
 	. "testing"
 	"time"
@@ -107,18 +108,11 @@ func TestSourceCLI(t *T) {
 	}
 }
 
-func TestSourceCLITailCallback(t *T) {
+func TestWithCLITail(t *T) {
 	ctx := context.Background()
 	ctx, _ = WithInt(ctx, "foo", 5, "")
 	ctx, _ = WithBool(ctx, "bar", "")
 
-	var tail []string
-	src := &SourceCLI{
-		TailCallback: func(gotTail []string) {
-			tail = gotTail
-		},
-	}
-
 	type testCase struct {
 		args    []string
 		expTail []string
@@ -127,7 +121,7 @@ func TestSourceCLITailCallback(t *T) {
 	cases := []testCase{
 		{
 			args:    []string{"--foo", "5"},
-			expTail: []string{},
+			expTail: nil,
 		},
 		{
 			args:    []string{"--foo", "5", "a", "b", "c"},
@@ -139,7 +133,7 @@ func TestSourceCLITailCallback(t *T) {
 		},
 		{
 			args:    []string{"--foo", "5", "--bar"},
-			expTail: []string{},
+			expTail: nil,
 		},
 		{
 			args:    []string{"--foo", "5", "--bar", "a", "b", "c"},
@@ -148,12 +142,25 @@ func TestSourceCLITailCallback(t *T) {
 	}
 
 	for _, tc := range cases {
-		tail = []string{}
-		src.Args = tc.args
-		err := Populate(ctx, src)
+		ctx, tail := WithCLITail(ctx)
+		err := Populate(ctx, &SourceCLI{Args: tc.args})
 		massert.Require(t, massert.Comment(massert.All(
 			massert.Nil(err),
-			massert.Equal(tc.expTail, tail),
+			massert.Equal(tc.expTail, *tail),
 		), "tc: %#v", tc))
 	}
 }
+
+func ExampleWithCLITail() {
+	ctx := context.Background()
+	ctx, foo := WithInt(ctx, "foo", 1, "Description of foo.")
+	ctx, tail := WithCLITail(ctx)
+	ctx, bar := WithString(ctx, "bar", "defaultVal", "Description of bar.")
+
+	err := Populate(ctx, &SourceCLI{
+		Args: []string{"--foo=100", "BADARG", "--bar", "BAR"},
+	})
+
+	fmt.Printf("err:%v foo:%v bar:%v tail:%#v\n", err, *foo, *bar, *tail)
+	// Output: err:<nil> foo:100 bar:defaultVal tail:[]string{"BADARG", "--bar", "BAR"}
+}

mcfg/env.go

@@ -43,7 +43,7 @@ func (env *SourceEnv) expectedName(path []string, name string) string {
 }
 
 // Parse implements the method for the Source interface
-func (env *SourceEnv) Parse(params []Param) ([]ParamValue, error) {
+func (env *SourceEnv) Parse(ctx context.Context, params []Param) ([]ParamValue, error) {
 	kvs := env.Env
 	if kvs == nil {
 		kvs = os.Environ()

mcfg/mcfg.go

@@ -72,7 +72,15 @@ func paramHash(path []string, name string) string {
 	return paramFullName(path, name) + "/" + hStr
 }
 
-func populate(params []Param, src Source) error {
+// Populate uses the Source to populate the values of all Params which were
+// added to the given Context, and all of its children. Populate may be called
+// multiple times with the same Context, each time will only affect the values
+// of the Params which were provided by the respective Source.
+//
+// Source may be nil to indicate that no configuration is provided. Only default
+// values will be used, and if any parameters are required this will error.
+func Populate(ctx context.Context, src Source) error {
+	params := collectParams(ctx)
 	if src == nil {
 		src = ParamValues(nil)
 	}
@@ -89,7 +97,7 @@ func populate(params []Param, src Source) error {
 		pM[hash] = p
 	}
 
-	pvs, err := src.Parse(params)
+	pvs, err := src.Parse(ctx, params)
 	if err != nil {
 		return err
 	}
@@ -127,14 +135,3 @@ func populate(params []Param, src Source) error {
 
 	return nil
 }
-
-// Populate uses the Source to populate the values of all Params which were
-// added to the given Context, and all of its children. Populate may be called
-// multiple times with the same Context, each time will only affect the values
-// of the Params which were provided by the respective Source.
-//
-// Source may be nil to indicate that no configuration is provided. Only default
-// values will be used, and if any parameters are required this will error.
-func Populate(ctx context.Context, src Source) error {
-	return populate(collectParams(ctx), src)
-}

mcfg/source.go

@@ -1,6 +1,7 @@
 package mcfg
 
 import (
+	"context"
 	"encoding/json"
 )
 
@@ -13,7 +14,8 @@ type ParamValue struct {
 }
 
 // Source parses ParamValues out of a particular configuration source, given a
-// sorted set of possible Params to parse.
+// sorted set of possible Params to parse, and the Context from with the Params
+// were extracted.
 //
 // Source should not return ParamValues which were not explicitly set to a value
 // by the configuration source.
@@ -23,7 +25,7 @@ type ParamValue struct {
 // ParamValues which do not correspond to any of the passed in Params. These
 // will be ignored in Populate.
 type Source interface {
-	Parse([]Param) ([]ParamValue, error)
+	Parse(context.Context, []Param) ([]ParamValue, error)
 }
 
 // ParamValues is simply a slice of ParamValue elements, which implements Parse
@@ -31,7 +33,7 @@ type Source interface {
 type ParamValues []ParamValue
 
 // Parse implements the method for the Source interface.
-func (pvs ParamValues) Parse([]Param) ([]ParamValue, error) {
+func (pvs ParamValues) Parse(context.Context, []Param) ([]ParamValue, error) {
 	return pvs, nil
 }
 
@@ -41,10 +43,10 @@ func (pvs ParamValues) Parse([]Param) ([]ParamValue, error) {
 type Sources []Source
 
 // Parse implements the method for the Source interface.
-func (ss Sources) Parse(params []Param) ([]ParamValue, error) {
+func (ss Sources) Parse(ctx context.Context, params []Param) ([]ParamValue, error) {
 	var pvs []ParamValue
 	for _, s := range ss {
-		innerPVs, err := s.Parse(params)
+		innerPVs, err := s.Parse(ctx, params)
 		if err != nil {
 			return nil, err
 		}

mcfg/source_test.go

@@ -143,7 +143,7 @@ func (scs srcCommonState) applyCtxAndPV(p srcCommonParams) srcCommonState {
 // ParamValues
 func (scs srcCommonState) assert(s Source) error {
 	root := scs.mkRoot()
-	gotPVs, err := s.Parse(collectParams(root))
+	gotPVs, err := s.Parse(root, collectParams(root))
 	if err != nil {
 		return err
 	}