ddtrace/ext: change error.msg to error.message for UNC (#1605)

Rename the `error.msg` tag to `error.message` tag in order to meet the
requirements of naming across all tracers.

ddtrace/ext/tags.go

@@ -68,7 +68,7 @@ const (
 	Error = "error"
 
 	// ErrorMsg specifies the error message.
-	ErrorMsg = "error.msg"
+	ErrorMsg = "error.message"
 
 	// ErrorType specifies the error type.
 	ErrorType = "error.type"

ddtrace/tracer/span_test.go

@@ -478,9 +478,9 @@ func TestSpanError(t *testing.T) {
 	err := errors.New("Something wrong")
 	span.SetTag(ext.Error, err)
 	assert.Equal(int32(1), span.Error)
-	assert.Equal("Something wrong", span.Meta["error.msg"])
-	assert.Equal("*errors.errorString", span.Meta["error.type"])
-	assert.NotEqual("", span.Meta["error.stack"])
+	assert.Equal("Something wrong", span.Meta[ext.ErrorMsg])
+	assert.Equal("*errors.errorString", span.Meta[ext.ErrorType])
+	assert.NotEqual("", span.Meta[ext.ErrorStack])
 
 	// operating on a finished span is a no-op
 	span = tracer.newRootSpan("flask.request", "flask", "/")
@@ -491,9 +491,9 @@ func TestSpanError(t *testing.T) {
 
 	// '+1' is `_dd.p.dm`
 	assert.Equal(nMeta+1, len(span.Meta))
-	assert.Equal("", span.Meta["error.msg"])
-	assert.Equal("", span.Meta["error.type"])
-	assert.Equal("", span.Meta["error.stack"])
+	assert.Equal("", span.Meta[ext.ErrorMsg])
+	assert.Equal("", span.Meta[ext.ErrorType])
+	assert.Equal("", span.Meta[ext.ErrorStack])
 }
 
 func TestSpanError_Typed(t *testing.T) {
@@ -505,9 +505,9 @@ func TestSpanError_Typed(t *testing.T) {
 	err := &boomError{}
 	span.SetTag(ext.Error, err)
 	assert.Equal(int32(1), span.Error)
-	assert.Equal("boom", span.Meta["error.msg"])
-	assert.Equal("*tracer.boomError", span.Meta["error.type"])
-	assert.NotEqual("", span.Meta["error.stack"])
+	assert.Equal("boom", span.Meta[ext.ErrorMsg])
+	assert.Equal("*tracer.boomError", span.Meta[ext.ErrorType])
+	assert.NotEqual("", span.Meta[ext.ErrorStack])
 }
 
 func TestSpanErrorNil(t *testing.T) {