[componenttest] Move CheckConfigStruct to confmaptest

.chloggen/deprecate-componenttest-checkconfigstruct.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: deprecation
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: componenttest
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Deprecate `componenttest.CheckConfigStruct`
+
+# One or more tracking issues or pull requests related to the change
+issues: [12580]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: Please use `confmaptest.CheckConfigStruct` instead.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

.chloggen/move-componenttest-checkconfigstruct.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confmaptest
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add `CheckConfigStruct` from `componenttest`
+
+# One or more tracking issues or pull requests related to the change
+issues: [12580]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext: This function validates struct field tags on config structs to ensure confmap can effectively unmarshal them.
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

cmd/mdatagen/internal/templates/component_test.go.tmpl

@@ -64,7 +64,7 @@ func TestComponentFactoryType(t *testing.T) {
 }
 
 func TestComponentConfigStruct(t *testing.T) {
-	require.NoError(t, componenttest.CheckConfigStruct(NewFactory().CreateDefaultConfig()))
+	require.NoError(t, confmaptest.CheckConfigStruct(NewFactory().CreateDefaultConfig()))
 }
 
 {{ if not (and .Tests.SkipLifecycle .Tests.SkipShutdown) -}}

component/component.go

@@ -182,7 +182,7 @@ type Factory interface {
 	// configuration and should not cause side effects that prevent the creation
 	// of multiple instances of the Component.
 	// The object returned by this method needs to pass the checks implemented by
-	// 'componenttest.CheckConfigStruct'. It is recommended to have these checks in the
+	// 'confmaptest.CheckConfigStruct'. It is recommended to have these checks in the
 	// tests of any implementation of the Factory interface.
 	CreateDefaultConfig() Config
 }

component/componenttest/configtest.go

@@ -20,6 +20,7 @@ var configFieldTagRegExp = regexp.MustCompile("^[a-z0-9][a-z0-9_]*$")
 // of components and extensions. It is recommended for implementers of components
 // to call this function on their tests passing the default configuration of the
 // component factory.
+// Deprecated: [v0.122.0] Use confmaptest.CheckConfigStruct instead.
 func CheckConfigStruct(config any) error {
 	t := reflect.TypeOf(config)
 	if t.Kind() == reflect.Ptr {

component/config.go

@@ -9,5 +9,5 @@ package component // import "go.opentelemetry.io/collector/component"
 // MUST implement xconfmap.Validator if any validation is required for that part of the configuration
 // (e.g. check if a required field is present).
 //
-// A valid implementation MUST pass the check componenttest.CheckConfigStruct (return nil error).
+// A valid implementation MUST pass the check confmaptest.CheckConfigStruct (return nil error).
 type Config any

confmap/confmaptest/configtest.go

@@ -7,13 +7,19 @@
 	"fmt"
 	"os"
 	"path/filepath"
+	"reflect"
 	"regexp"
+	"strings"
 
+	"go.uber.org/multierr"
 	"gopkg.in/yaml.v3"
 
 	"go.opentelemetry.io/collector/confmap"
 )
 
+// The regular expression for valid config field tag.
+var configFieldTagRegExp = regexp.MustCompile("^[a-z0-9][a-z0-9_]*$")
+
 // LoadConf loads a confmap.Conf from file, and does NOT validate the configuration.
 func LoadConf(fileName string) (*confmap.Conf, error) {
 	// Clean the path before using it.
@@ -47,3 +53,124 @@
 
 	return nil
 }
+
+// CheckConfigStruct enforces that given configuration object is following the patterns
+// used by the collector. This ensures consistency between different implementations
+// of components and extensions. It is recommended for implementers of components
+// to call this function on their tests passing the default configuration of the
+// component factory.
+func CheckConfigStruct(config any) error {
+	t := reflect.TypeOf(config)
+	if t.Kind() == reflect.Ptr {
+		t = t.Elem()
+	}
+
+	if t.Kind() != reflect.Struct {
+		return fmt.Errorf("config must be a struct or a pointer to one, the passed object is a %s", t.Kind())
+	}
+
+	return validateConfigDataType(t)
+}
+
+// validateConfigDataType performs a descending validation of the given type.
+// If the type is a struct it goes to each of its fields to check for the proper
+// tags.
+func validateConfigDataType(t reflect.Type) error {
+	var errs error
+
+	switch t.Kind() {
+	case reflect.Ptr:
+		errs = multierr.Append(errs, validateConfigDataType(t.Elem()))
+	case reflect.Struct:
+		// Reflect on the pointed data and check each of its fields.
+		nf := t.NumField()
+		for i := 0; i < nf; i++ {
+			f := t.Field(i)
+			errs = multierr.Append(errs, checkStructFieldTags(f))
+		}
+	default:
+		// The config object can carry other types but they are not used when
+		// reading the configuration via koanf so ignore them. Basically ignore:
+		// reflect.Uintptr, reflect.Chan, reflect.Func, reflect.Interface, and
+		// reflect.UnsafePointer.
+	}
+
+	if errs != nil {
+		return fmt.Errorf("type %q from package %q has invalid config settings: %w", t.Name(), t.PkgPath(), errs)
+	}
+
+	return nil
+}
+
+// checkStructFieldTags inspects the tags of a struct field.
+func checkStructFieldTags(f reflect.StructField) error {
+	tagValue := f.Tag.Get(confmap.MapstructureTag)
+	if tagValue == "" {
+		// Ignore special types.
+		switch f.Type.Kind() {
+		case reflect.Interface, reflect.Chan, reflect.Func, reflect.Uintptr, reflect.UnsafePointer:
+			// Allow the config to carry the types above, but since they are not read
+			// when loading configuration, just ignore them.
+			return nil
+		}
+
+		// Public fields of other types should be tagged.
+		chars := []byte(f.Name)
+		if len(chars) > 0 && chars[0] >= 'A' && chars[0] <= 'Z' {
+			return fmt.Errorf("mapstructure tag not present on field %q", f.Name)
+		}
+
+		// Not public field, no need to have a tag.
+		return nil
+	}
+
+	tagParts := strings.Split(tagValue, ",")
+	if tagParts[0] != "" {
+		if tagParts[0] == "-" {
+			// Nothing to do, as mapstructure decode skips this field.
+			return nil
+		}
+	}
+
+	// Check if squash is specified.
+	squash := false
+	for _, tag := range tagParts[1:] {
+		if tag == "squash" {
+			squash = true
+			break
+		}
+	}
+
+	if squash {
+		// Field was squashed.
+		if (f.Type.Kind() != reflect.Struct) && (f.Type.Kind() != reflect.Ptr || f.Type.Elem().Kind() != reflect.Struct) {
+			return fmt.Errorf(
+				"attempt to squash non-struct type on field %q", f.Name)
+		}
+	}
+
+	switch f.Type.Kind() {
+	case reflect.Struct:
+		// It is another struct, continue down-level.
+		return validateConfigDataType(f.Type)
+
+	case reflect.Map, reflect.Slice, reflect.Array:
+		// The element of map, array, or slice can be itself a configuration object.
+		return validateConfigDataType(f.Type.Elem())
+
+	default:
+		fieldTag := tagParts[0]
+		if !configFieldTagRegExp.MatchString(fieldTag) {
+			if f.Name == "AdditionalProperties" {
+				return nil
+			}
+			return fmt.Errorf(
+				"field %q has config tag %q which doesn't satisfy %q",
+				f.Name,
+				fieldTag,
+				configFieldTagRegExp.String())
+		}
+	}
+
+	return nil
+}