Improved vdiffr setup (tidyverse#2856)

* create vdiffr validation failure in segment annotations test

* run vdiffr on travis only on current R release

* use environment variable USE_VDIFFR

* fix broken reference image

* try simpler setup for Travis

* finalize vdiffr setup

.travis.yml

@@ -3,27 +3,29 @@ cache: packages
 sudo: true
 dist: trusty
 
-addons:
-  apt:
-    packages:
-      - libfreetype6
-
-r:
-- 3.1
-- 3.2
-- oldrel
-- release
-- devel
+# build matrix; turn on vdiffr only on r release
+matrix:
+  include:
+  - r: devel
+  - r: release
+    env: USE_VDIFFR=true
+  - r: oldrel
+  - r: 3.2
+  - r: 3.1
 
 # work around temporary travis + R 3.5 bug
 r_packages: devtools
 
 # Install manually because dev vdiffr is not compatible with Appveyor yet
 r_github_packages: lionel-/vdiffr
 
+# environment variables set for all builds
 env:
   global:
+  # don't treat missing suggested packages as error
   - _R_CHECK_FORCE_SUGGESTS_=false
+  # switch off vdiffr by default
+  - USE_VDIFFR=false
 
 after_success:
   - Rscript -e 'covr::codecov()'

tests/testthat/helper-vdiffr.R

@@ -1,12 +1,16 @@
+# default is equal to whether NOT_CRAN is true or not
+enable_vdiffr <- identical(Sys.getenv("NOT_CRAN"), "true")
 
-enable_vdiffr <- TRUE
-
-if (!requireNamespace("vdiffr", quietly = TRUE) ||
-  utils::packageVersion("vdiffr") < "0.2.3.9000") {
+# disable or enable vdiffr based on the state of USE_VDIFFR, if set
+if (identical(Sys.getenv("USE_VDIFFR"), "true")) {
+  enable_vdiffr <- TRUE
+} else if (identical(Sys.getenv("USE_VDIFFR"), "false")) {
   enable_vdiffr <- FALSE
 }
 
-if (paste(R.Version()$major, R.Version()$minor, sep = ".") < "3.3.0") {
+# disable vdiffr if version is too old
+if (!requireNamespace("vdiffr", quietly = TRUE) ||
+  utils::packageVersion("vdiffr") < "0.2.3.9000") {
   enable_vdiffr <- FALSE
 }