downgrade pre-commit for pip installation so that it is the last version that supports python2, which is the system installation on the travis image

Author: lorenzwalthert

.travis.yml

@@ -50,7 +50,7 @@ jobs:
     env: 
       - EXTERNAL_INSTALLATION="TRUE"
     before_script:
-      - pip install pre-commit --user
+      - pip install pre-commit==v1.21.0 --user 
       - R -q -e 'tic::before_script()'
       - R -q -e 'remove.packages("reticulate")' # only used for installation and uninstallation.
   - name: macOS_brew # install pre-commit outside
@@ -67,7 +67,7 @@ jobs:
     env: 
       - EXTERNAL_INSTALLATION="TRUE"
     before_script:
-      - pip install pre-commit --user
+      - pip install pre-commit==v1.21.0 --user 
       - R -q -e 'tic::before_script()'
       - R -q -e 'remove.packages("reticulate")' # only used for installation and uninstallation.
 

tests/testthat/test-assumptions.R

@@ -1,7 +1,18 @@
 test_that("documentation regarding desc is still accurate", {
   skip_on_cran()
-    versions <- versions::available.versions("desc")
-    if (max(as.package_version(versions$desc$version)) > "1.2") {
-      rlang::abort("newer version of desc on CRAN. Adapt the warning and maybe add minimal version requirement?")
-    }
+  versions <- versions::available.versions("desc")
+  if (max(as.package_version(versions$desc$version)) > "1.2") {
+    rlang::abort("newer version of desc on CRAN. Adapt the warning and maybe add minimal version requirement?")
+  }
+})
+
+test_that("use python3 with pip installations", {
+  if (Sys.Date() > as.Date("2020-09-30")) {
+    rlang::abort(paste0(
+      "Please unpin version requirement for pre-commit in .travis.yml ",
+      "for pip installations and make things work with Python3. Currently ",
+      "pinned version 1.21 is the last with python2 support, which is the ",
+      "system python in the travis R image as of May 2020."
+    ))
+  }
 })