generic step_run_code(), closes #1, closes #3

- New `step_run_code()` to run arbitrary code. If the code is a call with the `pkg::fun()`, notation, pkg is installed if missing (#1, #3). `step_run_covr()` remains for compatibility but is scheduled for removal.

DESCRIPTION

@@ -39,6 +39,7 @@ Collate:
     'run.R'
     'stage.R'
     'steps-base.R'
+    'steps-code.R'
     'steps-covr.R'
     'steps-git.R'
     'steps-pkgdown.R'

NAMESPACE

@@ -22,6 +22,7 @@ export(step_build_pkgdown)
 export(step_hello_world)
 export(step_install_ssh_keys)
 export(step_push_deploy)
+export(step_run_code)
 export(step_run_covr)
 export(step_test_ssh)
 importFrom(R6,R6Class)

R/steps-code.R

@@ -0,0 +1,31 @@
+RunCode <- R6Class(
+  "RunCode", inherit = TicStep,
+
+  public = list(
+    initialize = function(call) {
+      call <- substitute(call)
+      private$call <- call
+    },
+
+    run = function() {
+      eval(private$call, envir = baseenv())
+    },
+
+    prepare = function() {
+      func_name <- private$call[[1]]
+      if (is.call(func_name) && func_name[[1]] == quote(`::`)) {
+        pkg_name <- as.character(func_name[[2]])
+        if (!requireNamespace(pkg_name, quietly = TRUE)) {
+          install.packages(pkg_name)
+        }
+      }
+    }
+  ),
+
+  private = list(
+    call = NULL
+  )
+)
+
+#' @export
+step_run_code <- RunCode$new