Offer the reference hint only where it would render the same value, and name the guard set in the help

builtins.go

@@ -133,7 +133,7 @@ func transformArg(fields map[string]node, a []string) error {
 		_, _, err := refShape(leaf)
 		return err
 	}
-	return checkArm(leaf, fields)
+	return checkArm(leaf, fields, false)
 }
 
 func transformOperand(a []string) []string {

cmd/fejkdata/main.go

@@ -31,7 +31,8 @@ An argument containing a { token, or a JSON object, array or string, is a
 template; any other argument is a path (a path never contains a brace, a bracket
 or a quote). Templates reach the data by reference from the root —
 {/sv_SE.person.last} — whether the data is shipped or layered with --data-path. An
-argument carrying one of those characters but no valid JSON names neither.
+argument carrying a bracket, a closing brace or a quote but no valid JSON names
+neither.
 
   -d, --data-path D      a data directory to layer over the shipped data (repeatable; last wins on a clash)
   -h, --help             print this help, then exit

cmd/fejkdata/main_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"os"
 	"path/filepath"
+	"regexp"
 	"strings"
 	"testing"
 )
@@ -333,6 +334,15 @@ func TestClassify(t *testing.T) {
 	}
 }
 
+func TestUsageReferencesResolve(t *testing.T) {
+	for _, token := range regexp.MustCompile(`\{/[^}]+\}`).FindAllString(usage, -1) {
+		code, out, errb := runOut("--seed", "1", token)
+		if code != 0 || strings.TrimSpace(out) == "" {
+			t.Errorf("usage advertises %s: run = %d, %q, stderr %q", token, code, out, errb)
+		}
+	}
+}
+
 func TestRunShapeMisuseBeforeLoad(t *testing.T) {
 	code, _, errb := runOut("--no-shipped-data", "[abc]")
 	if code != 2 || !strings.Contains(errb, "[abc]") || strings.Contains(errb, "--data-path") {

inline_test.go

@@ -83,12 +83,16 @@ func TestFieldlessTokenHint(t *testing.T) {
 		t.Fatalf("FakeTemplate(bare token) = %v, want a hint naming {/sv_SE.person.last}", err)
 	}
 	_, err = f.FakeTemplate(`{"format":"{x}","repeat":2}`)
-	if err == nil || strings.Contains(err.Error(), "bare string") {
+	if err == nil || !strings.Contains(err.Error(), `this template has none — write {/x}`) {
-		t.Errorf("FakeTemplate(fieldless object) = %v, want an error that does not call it a bare string", err)
+		t.Errorf("FakeTemplate(fieldless object) = %v, want the hint without calling it a bare string", err)
 	}
-	_, err = f.FakeTemplate(`{ /sv_SE.person.last }`)
+	// A hint is only a drop-in where the name is the whole token: {/x} inside a
-	if err == nil || strings.Contains(err.Error(), "write {") {
+	// transform or an alternation renders a different value, so none is offered.
-		t.Errorf("FakeTemplate(malformed token) = %v, want no hint naming a spelling that fails too", err)
+	for _, input := range []string{`{ /sv_SE.person.last }`, "{lowercase(x)}", "{x|y}"} {
+		_, err := f.FakeTemplate(input)
+		if err == nil || strings.Contains(err.Error(), "write {") {
+			t.Errorf("FakeTemplate(%q) = %v, want no hint naming a spelling that means something else", input, err)
+		}
 	}
 }
 
@@ -105,7 +109,7 @@ func TestFakeTemplateErrors(t *testing.T) {
 		{`name: {..nope}`, "write {/nope}"},
 		{`{"format":"x"}`, "is a string"},
 		{`{/misc.country} {/misc.country.alpha2}`, "renders a level"},
-		{`{"format":"{/misc.country.alpha2} {x}","x":"{/misc.country}"}`, "renders"},
+		{`{"format":"{/misc.country.alpha2} {x}","x":"{/misc.country}"}`, "reads a path into"},
 	} {
 		_, err := f.FakeTemplate(c.input)
 		if err == nil || !strings.Contains(err.Error(), c.want) {

template.go

@@ -140,7 +140,7 @@ func checkTokens(format string, fields map[string]node) error {
 				}
 				continue // its target is checked at New (see linkRefs)
 			}
-			if err := checkArm(name, fields); err != nil {
+			if err := checkArm(name, fields, len(names) == 1); err != nil {
 				return fmt.Errorf("token {%s}: %w", t.body, err)
 			}
 		}
@@ -151,7 +151,9 @@ func checkTokens(format string, fields map[string]node) error {
 }
 
 // checkArm validates one sibling name or path against a template's fields.
-func checkArm(name string, fields map[string]node) error {
+// wholeToken says the name is the token's entire body, so {/name} would render
+// the same value and can be offered as the reference spelling.
+func checkArm(name string, fields map[string]node, wholeToken bool) error {
 	a := splitArm(name, nil)
 	if err := checkSegments(a); err != nil {
 		return err
@@ -166,7 +168,7 @@ func checkArm(name string, fields map[string]node) error {
 		}
 		if len(fields) == 0 {
 			hint := ""
-			if hintableRef(name) {
+			if wholeToken && hintableRef(name) {
 				hint = fmt.Sprintf(" — write {/%s} to reference the data", name)
 			}
 			return fmt.Errorf("no field %q; a token names a sibling field, and this template has none%s", a.key, hint)