Introduce "split" metric schema transformation

This is a new transformation type that allows to describe a change
where a metric is converted to several other metrics by eliminating
an attribute.

An example of such change that happened recently is this:
open-telemetry/opentelemetry-specification#2617

This PR implements specification change open-telemetry/opentelemetry-specification#2653

This PR creates package v1.1 for the new functionality. The old package v1.0
remains unchanged.

schema/README.md

@@ -11,9 +11,9 @@ then import the corresponding package and use the `Parse` or `ParseFile` functio
 like this:
 
 ```go
-import schema "go.opentelemetry.io/otel/schema/v1.0"
+import schema "go.opentelemetry.io/otel/schema/v1.1"
 
-// Load the schema from a file in v1.0.x file format.
+// Load the schema from a file in v1.1.x file format.
 func loadSchemaFromFile() error {
 	telSchema, err := schema.ParseFile("schema-file.yaml")
 	if err != nil {

schema/internal/parser_checks.go

@@ -0,0 +1,58 @@
+package internal
+
+import (
+	"fmt"
+	"net/url"
+	"strconv"
+	"strings"
+
+	"github.com/Masterminds/semver/v3"
+)
+
+// CheckFileFormatField validates the file format field according to the rules here:
+// https://github.com/open-telemetry/oteps/blob/main/text/0152-telemetry-schemas.md#schema-file-format-number
+func CheckFileFormatField(fileFormat string, supportedFormatMajor, supportedFormatMinor int) error {
+	// Verify that the version number in the file is a semver.
+	fileFormatParsed, err := semver.StrictNewVersion(fileFormat)
+	if err != nil {
+		return fmt.Errorf(
+			"invalid schema file format version number %q (expected semver): %w",
+			fileFormat, err,
+		)
+	}
+
+	// Check that the major version number in the file is the same as what we expect.
+	if fileFormatParsed.Major() != uint64(supportedFormatMajor) {
+		return fmt.Errorf(
+			"this library cannot parse file formats with major version other than %v",
+			supportedFormatMajor,
+		)
+	}
+
+	// Check that the file minor version number is not greater than
+	// what is requested supports.
+	if fileFormatParsed.Minor() > uint64(supportedFormatMinor) {
+		supportedFormatMajorMinor := strconv.Itoa(supportedFormatMajor) + "." +
+			strconv.Itoa(supportedFormatMinor) // 1.0
+
+		return fmt.Errorf(
+			"unsupported schema file format minor version number, expected no newer than %v, got %v",
+			supportedFormatMajorMinor+".x", fileFormat,
+		)
+	}
+
+	// Patch, prerelease and metadata version number does not matter, so we don't check it.
+
+	return nil
+}
+
+func CheckSchemaURL(schemaURL string) error {
+	if strings.TrimSpace(schemaURL) == "" {
+		return fmt.Errorf("schema_url field is missing")
+	}
+
+	if _, err := url.Parse(schemaURL); err != nil {
+		return fmt.Errorf("invalid URL specified in schema_url field: %w", err)
+	}
+	return nil
+}

schema/v1.0/parser.go

@@ -15,14 +15,10 @@
 package schema // import "go.opentelemetry.io/otel/schema/v1.0"
 
 import (
-	"fmt"
 	"io"
-	"net/url"
 	"os"
-	"strconv"
-	"strings"
 
-	"github.com/Masterminds/semver/v3"
+	"go.opentelemetry.io/otel/schema/internal"
 	"gopkg.in/yaml.v2"
 
 	"go.opentelemetry.io/otel/schema/v1.0/ast"
@@ -34,10 +30,6 @@ const supportedFormatMajor = 1
 // Maximum minor version number that this library supports.
 const supportedFormatMinor = 0
 
-// Maximum major+minor version number that this library supports, as a string.
-var supportedFormatMajorMinor = strconv.Itoa(supportedFormatMajor) + "." +
-	strconv.Itoa(supportedFormatMinor) // 1.0
-
 // ParseFile a schema file. schemaFilePath is the file path.
 func ParseFile(schemaFilePath string) (*ast.Schema, error) {
 	file, err := os.Open(schemaFilePath)
@@ -56,51 +48,15 @@ func Parse(schemaFileContent io.Reader) (*ast.Schema, error) {
 		return nil, err
 	}
 
-	if err := checkFileFormatField(ts.FileFormat); err != nil {
+	err = internal.CheckFileFormatField(ts.FileFormat, supportedFormatMajor, supportedFormatMinor)
+	if err != nil {
 		return nil, err
 	}
 
-	if strings.TrimSpace(ts.SchemaURL) == "" {
-		return nil, fmt.Errorf("schema_url field is missing")
-	}
-
-	if _, err := url.Parse(ts.SchemaURL); err != nil {
-		return nil, fmt.Errorf("invalid URL specified in schema_url field: %w", err)
-	}
-
-	return &ts, nil
-}
-
-// checkFileFormatField validates the file format field according to the rules here:
-// https://github.com/open-telemetry/oteps/blob/main/text/0152-telemetry-schemas.md#schema-file-format-number
-func checkFileFormatField(fileFormat string) error {
-	// Verify that the version number in the file is a semver.
-	fileFormatParsed, err := semver.StrictNewVersion(fileFormat)
+	err = internal.CheckSchemaURL(ts.SchemaURL)
 	if err != nil {
-		return fmt.Errorf(
-			"invalid schema file format version number %q (expected semver): %w",
-			fileFormat, err,
-		)
-	}
-
-	// Check that the major version number in the file is the same as what we expect.
-	if fileFormatParsed.Major() != supportedFormatMajor {
-		return fmt.Errorf(
-			"this library cannot parse file formats with major version other than %v",
-			supportedFormatMajor,
-		)
-	}
-
-	// Check that the file minor version number is not greater than
-	// what is requested supports.
-	if fileFormatParsed.Minor() > supportedFormatMinor {
-		return fmt.Errorf(
-			"unsupported schema file format minor version number, expected no newer than %v, got %v",
-			supportedFormatMajorMinor+".x", fileFormat,
-		)
+		return nil, err
 	}
 
-	// Patch, prerelease and metadata version number does not matter, so we don't check it.
-
-	return nil
+	return &ts, nil
 }