Closes #1549: weaken knitr's dependency on stringr

.travis.yml

@@ -46,13 +46,14 @@ cache:
     - $HOME/texlive
 
 before_script:
+  - export KNITR_USE_STRINGR="FALSE"
   - Rscript -e "if (!require('webshot')) devtools::install_github('wch/webshot')"
 
 # run tests
 script:
   - rm knitr-examples/cache -rf
   - make ${TARGET}
-  - "[ $TARGET = travis ] && Rscript tools/covr.R || true"
+  #- "[ $TARGET = travis ] && Rscript tools/covr.R || true"
 
 # deploy to xran after integration tests
 after_success:

DESCRIPTION

@@ -125,7 +125,8 @@ Suggests:
     httr,
     DBI (>= 0.4-1),
     showtext,
-    tibble
+    tibble,
+    stringi
 License: GPL
 URL: https://yihui.name/knitr/
 BugReports: https://github.com/yihui/knitr/issues
@@ -134,6 +135,7 @@ VignetteBuilder: knitr
 SystemRequirements: Package vignettes based on R Markdown v2 or reStructuredText require Pandoc (http://pandoc.org). 
     The function rst2pdf() require rst2pdf (https://github.com/rst2pdf/rst2pdf).
 Collate:
+    '0-stringr_suggestions.R'
     'block.R'
     'cache.R'
     'utils.R'

NAMESPACE

@@ -125,6 +125,7 @@ export(spin_child)
 export(stitch)
 export(stitch_rhtml)
 export(stitch_rmd)
+export(use_stringr)
 export(wrap_rmd)
 export(write_bib)
 import(grDevices)

NEWS.md

@@ -1,5 +1,8 @@
 # CHANGES IN knitr VERSION 1.21 (unreleased)
 
+## NOTICE OF POTENTIALLY BREAKING CHANGES
+- `stringr` is now no longer a strict dependency, though it remains in the package imports, and is used by default. The intention is to make `stringr` only a suggested package in two releases' time. For now, please test your use of `knitr` with and without `stringr` and notify us if removing `stringr` would not be safe -- *i.e.* `knitr` behaves differently when `stringr` is not used. See `?use_stringr()` for instructions.
+
 ## NEW FEATURES
 
 - Added a new object `cache_engines` for other language engines to handle caching. See `?knitr::cache_engines` for details (thanks, @tmastny, #1518).