feat(gnoland): in config, refer to fields using toml struct tags (#…

…1769)

After briefly discussing #1605, me and @zivkovicmilos convened that it
would be better if the `config` commands took, for the keys in the
configuration, their TOML name rather than the internal Go struct field
name. This PR implements that.

gno.land/cmd/gnoland/config.go

@@ -4,6 +4,7 @@ import (
 	"flag"
 	"fmt"
 	"reflect"
+	"strings"
 
 	"github.com/gnolang/gno/tm2/pkg/commands"
 )
@@ -47,7 +48,7 @@ func (c *configCfg) RegisterFlags(fs *flag.FlagSet) {
 func getFieldAtPath(currentValue reflect.Value, path []string) (*reflect.Value, error) {
 	// Look at the current section, and figure out if
 	// it's a part of the current struct
-	field := currentValue.FieldByName(path[0])
+	field := fieldByTOMLName(currentValue, path[0])
 	if !field.IsValid() || !field.CanSet() {
 		return nil, newInvalidFieldError(path[0], currentValue)
 	}
@@ -67,24 +68,84 @@ func getFieldAtPath(currentValue reflect.Value, path []string) (*reflect.Value,
 	return &field, nil
 }
 
-// newInvalidFieldError creates an error for non-existent struct fields
-// being passed as arguments to [getFieldAtPath]
-func newInvalidFieldError(field string, value reflect.Value) error {
-	var (
-		valueType = value.Type()
-		numFields = value.NumField()
-	)
-
-	fields := make([]string, 0, numFields)
+func fieldByTOMLName(value reflect.Value, name string) reflect.Value {
+	var dst reflect.Value
+	eachTOMLField(value, func(val reflect.Value, tomlName string) bool {
+		if tomlName == name {
+			dst = val
+			return true
+		}
+		return false
+	})
+	return dst
+}
 
-	for i := 0; i < numFields; i++ {
-		valueField := valueType.Field(i)
-		if !valueField.IsExported() {
+// eachTOMLField iterates over each field in value (assumed to be a struct).
+// For every field within the struct, iterationCallback is called with the value
+// of the field and the associated name in the TOML representation
+// (through the `toml:"..."` struct field, or just the field's name as fallback).
+// If iterationCallback returns true, the function returns immediately with
+// true. If it always returns false, or no fields were processed, eachTOMLField
+// will return false.
+func eachTOMLField(value reflect.Value, iterationCallback func(val reflect.Value, tomlName string) bool) bool {
+	// For reference:
+	// https://github.com/pelletier/go-toml/blob/7dad87762adb203e30b96a46026d1428ef2491a2/unmarshaler.go#L1251-L1270
+
+	currentType := value.Type()
+	nf := currentType.NumField()
+	for i := 0; i < nf; i++ {
+		fld := currentType.Field(i)
+		tomlName := fld.Tag.Get("toml")
+
+		// Ignore `toml:"-"`, strip away any "omitempty" or other options.
+		if tomlName == "-" || !fld.IsExported() {
 			continue
 		}
+		if pos := strings.IndexByte(tomlName, ','); pos != -1 {
+			tomlName = tomlName[:pos]
+		}
+
+		// Handle anonymous (embedded) fields.
+		// Anonymous fields will be treated regularly if they have a tag.
+		if fld.Anonymous && tomlName == "" {
+			anon := fld.Type
+			if anon.Kind() == reflect.Ptr {
+				anon = anon.Elem()
+			}
+
+			if anon.Kind() == reflect.Struct {
+				// NOTE: naive, if there is a conflict the embedder should take
+				// precedence over the embedded; but the TOML parser seems to
+				// ignore this, too, and this "unmarshaler" isn't fit for general
+				// purpose.
+				if eachTOMLField(value.Field(i), iterationCallback) {
+					return true
+				}
+				continue
+			}
+			// If it's not a struct, or *struct, it should be treated regularly.
+		}
 
-		fields = append(fields, valueField.Name)
+		// general case, simple struct field.
+		if tomlName == "" {
+			tomlName = fld.Name
+		}
+		if iterationCallback(value.Field(i), tomlName) {
+			return true
+		}
 	}
+	return false
+}
+
+// newInvalidFieldError creates an error for non-existent struct fields
+// being passed as arguments to [getFieldAtPath]
+func newInvalidFieldError(field string, value reflect.Value) error {
+	fields := make([]string, 0, value.NumField())
+
+	eachTOMLField(value, func(val reflect.Value, tomlName string) bool {
+		fields = append(fields, tomlName)
+		return false
+	})
 
 	return fmt.Errorf(
 		"field %q, is not a valid configuration key, available keys: %s",