Update Tracer configuration.

Conform to API option design outlined in #536.

Add tests to validate new TracerConfigure function

Drop the `instrumentation` prefix.

api/trace/api.go

@@ -24,30 +24,46 @@ import (
 
 type Provider interface {
 	// Tracer creates an implementation of the Tracer interface.
-	// The instrumentationName must be the name of the library providing
-	// instrumentation. This name may be the same as the instrumented code
-	// only if that code provides built-in instrumentation. If the
-	// instrumentationName is empty, then a implementation defined default
-	// name will be used instead.
-	Tracer(instrumentationName string, opts ...TracerOption) Tracer
+	// The passed name must be the package name of the instrumentation
+	// library, this is the library that provids instrumentation. It should
+	// not be the name of the library being instrumented unless that code
+	// itself is providing built-in instrumentation. If the name is empty,
+	// then an implementation defined default name will be used instead.
+	Tracer(name string, options ...TracerOption) Tracer
 }
 
-// TODO (MrAlias): unify this API option design:
-// https://github.com/open-telemetry/opentelemetry-go/issues/536
-
-// TracerConfig contains options for a Tracer.
+// TracerConfig is a group of options for a Tracer.
 type TracerConfig struct {
-	InstrumentationVersion string
+	// Version is the version of the instrumentation library.
+	Version string
 }
 
-// TracerOption configures a TracerConfig option.
-type TracerOption func(*TracerConfig)
-
-// WithInstrumentationVersion sets the instrumentation version for a Tracer.
-func WithInstrumentationVersion(version string) TracerOption {
-	return func(c *TracerConfig) {
-		c.InstrumentationVersion = version
+// TracerConfigure applies all the options to a returned TracerConfig.
+// The default value for all the fields of the returned TracerConfig are the
+// default zero value of the type. Also, this does not perform any validation
+// on the returned TracerConfig (e.g. no uniqueness checking or bounding of
+// data), instead it is left to the implementations of the SDK to perform this
+// action.
+func TracerConfigure(options []TracerOption) *TracerConfig {
+	config := new(TracerConfig)
+	for _, option := range options {
+		option.Apply(config)
 	}
+	return config
+}
+
+// TracerOption applies an options to a TracerConfig.
+type TracerOption interface {
+	Apply(*TracerConfig)
+}
+
+type versionTracerOption string
+
+func (o versionTracerOption) Apply(c *TracerConfig) { c.Version = string(o) }
+
+// WithVersion sets the instrumentation version for a Tracer.
+func WithVersion(version string) TracerOption {
+	return versionTracerOption(version)
 }
 
 type Tracer interface {

api/trace/traceprovider_test.go

@@ -0,0 +1,57 @@
+// Copyright The OpenTelemetry Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package trace
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTracerConfigure(t *testing.T) {
+	v1 := "semver:0.0.1"
+	v2 := "semver:1.0.0"
+	tests := []struct {
+		options  []TracerOption
+		expected *TracerConfig
+	}{
+		{
+			// No non-zero-values should be set.
+			[]TracerOption{},
+			new(TracerConfig),
+		},
+		{
+			[]TracerOption{
+				WithVersion(v1),
+			},
+			&TracerConfig{
+				Version: v1,
+			},
+		},
+		{
+			[]TracerOption{
+				// Multiple calls should overwrite.
+				WithVersion(v1),
+				WithVersion(v2),
+			},
+			&TracerConfig{
+				Version: v2,
+			},
+		},
+	}
+	for _, test := range tests {
+		assert.Equal(t, test.expected, TracerConfigure(test.options))
+	}
+}