style: Added a log when going the legacy path

config/config.go

@@ -111,6 +111,7 @@ func (c *ConfigCompiler) ConfigQuery(
 	configCompilationResp := &ConfigResponse{}
 	statusCode, originalErr := c.compileRestClient.DoRequest(req, configCompilationResp)
 	if statusCode == 404 {
+		fmt.Fprintf(os.Stderr, "You are using a old version of CircleCI Server, please consider updating")
 		legacyResponse, err := c.legacyConfigQueryByOrgID(configString, orgID, params, values, c.cfg)
 		if err != nil {
 			return nil, err

config/legacy_test.go

@@ -71,6 +71,41 @@ func TestLegacyFlow(t *testing.T) {
 		})
 		_, err := compiler.ConfigQuery("testdata/config.yml", "1234", Parameters{}, Values{})
 		assert.Error(t, err)
-		assert.Contains(t, "failed to validate", err.Error())
+		assert.Contains(t, err.Error(), "failed to validate")
+	})
+
+	t.Run("tests that the compiler fails out completely when a non-404 is returned from the http endpoint", func(t *testing.T) {
+		mux := http.NewServeMux()
+		gqlHitCounter := 0
+
+		mux.HandleFunc("/compile-config-with-defaults", func(w http.ResponseWriter, r *http.Request) {
+			w.WriteHeader(http.StatusInternalServerError)
+
+		})
+
+		mux.HandleFunc("/me/collaborations", func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintf(w, `[{"vcs_type":"circleci","slug":"gh/test","id":"2345"}]`)
+		})
+
+		mux.HandleFunc("/graphql-unstable", func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "application/json")
+			fmt.Fprintf(w, `{"data":{"buildConfig":{"errors":[{"message": "failed to validate"}]}}}`)
+			gqlHitCounter++
+		})
+
+		svr := httptest.NewServer(mux)
+		defer svr.Close()
+
+		compiler := New(&settings.Config{
+			Host:       svr.URL,
+			Endpoint:   "/graphql-unstable",
+			HTTPClient: http.DefaultClient,
+			Token:      "",
+		})
+		_, err := compiler.ConfigQuery("testdata/config.yml", "1234", Parameters{}, Values{})
+		assert.Error(t, err)
+		assert.Contains(t, err.Error(), "config compilation request returned an error:")
+		assert.Equal(t, 0, gqlHitCounter)
 	})
 }