refactor: Make parse errors less verbose

* The errors raised by `ArgumentParser()$parse_args()` are now of class "argparse_parse_error".

  They are now less verbose when `interactive()` is `FALSE` (#40).

  There may still a trailing "Execution halted" line output by R's default error handler
  (when `interactive()` is `FALSE`).
  This can be silenced by setting a new error handler near the top of your Rscript e.g.

  ```r
  if (!interactive())
      options(error=function(e) quit('no', status = 1, runLast = FALSE))
  ```

closes #40

DESCRIPTION

@@ -1,8 +1,8 @@
 Package: argparse
 Type: Package
 Title: Command Line Optional and Positional Argument Parser
-Version: 2.1.5
-Authors@R: c(person("Trevor L", "Davis", role=c("aut", "cre"), 
+Version: 2.1.6
+Authors@R: c(person("Trevor L", "Davis", role=c("aut", "cre"),
              email="[email protected]",
              comment = c(ORCID = "0000-0001-6341-4639")),
     person("Allen", "Day", role="ctb", comment="Some documentation and examples ported from the getopt package."),
@@ -16,6 +16,8 @@ Copyright: See file (inst/)COPYRIGHTS.
 URL: https://github.com/trevorld/r-argparse
 BugReports: https://github.com/trevorld/r-argparse/issues
 LazyLoad: yes
+Depends:
+    R (>= 3.6.0)
 Imports:
     R6,
     findpython,

NEWS.md

@@ -1,3 +1,19 @@
+argparse 2.1.6
+==============
+
+* The errors raised by `ArgumentParser()$parse_args()` are now of class "argparse_parse_error".
+
+  They are now less verbose when `interactive()` is `FALSE` (#40).
+
+  There may still a trailing "Execution halted" line output by R's default error handler
+  (when `interactive()` is `FALSE`).
+  This can be silenced by setting a new error handler near the top of your Rscript e.g.
+
+  ```r
+  if (!interactive())
+      options(error=function(e) quit('no', status = 1, runLast = FALSE))
+  ```
+
 argparse 2.1.5
 ==============
 

R/argparse.R

@@ -202,27 +202,27 @@ parse_args_output <- function(output) {
         has_positional_arguments <- any(grepl("^positional arguments:", output))
         has_optional_arguments <- any(grepl("^optional arguments:|^options:", output))
         if (has_positional_arguments || has_optional_arguments) {
-            .print_message_and_exit(output, "help requested:")
+            print_message_and_exit(output, "help requested:")
         } else {
-            .stop(output, "parse error:")
+            pa_stop(output)
         }
     } else if (grepl("^Traceback", output[1])) {
-        .stop(output, "Error: python error")
+        pa_stop(output)
     } else if (any(grepl("^SyntaxError: Non-ASCII character", output))) {
         message <- paste("Non-ASCII character detected.",
                        "If you wish to use Unicode arguments/options",
                        "please upgrade to Python 3.2+",
                        "Please see file INSTALL for more details.")
-        .stop(message, "non-ascii character error:")
+        pa_stop(message)
     } else if (any(grepl("^SyntaxError: positional argument follows keyword argument", output)) ||
                grepl("^SyntaxError: non-keyword arg after keyword arg", output[2])) {
         message <- "Positional argument following keyword argument."
-        .stop(message, "syntax error:")
+        pa_stop(message)
     } else if (grepl("^\\{|^\\[", output)) {
         args <- jsonlite::fromJSON(paste(output, collapse = ""))
         return(args)
     } else { # presumably version number request
-        .print_message_and_exit(output, "version requested:")
+        print_message_and_exit(output, "version requested:")
     }
 }
 
@@ -358,16 +358,28 @@ find_python_cmd <- function(python_cmd = NULL) {
     python_cmd
 }
 
-.stop <- function(message, r_note) {
-        stop(paste(r_note, paste(message, collapse = "\n"), sep = "\n"))
+pa_stop <- function(message) {
+    msg <- paste(c("argparse_parse_error", message), collapse = "\n")
+    cnd <- errorCondition(msg,
+                          call = "argparse::parse_args_output(output)",
+                          class = "argparse_parse_error")
+    if (interactive()) {
+        stop(cnd)
+    } else {
+        signalCondition(cnd)
+        cat(message, sep = "\n", file = stderr())
+        opt <- options(show.error.messages = FALSE)
+        on.exit(options(opt))
+        stop(cnd)
+    }
 }
 
 # Internal function to print message
-.print_message_and_exit <- function(message, r_note) {
+print_message_and_exit <- function(message, r_note, status = 0) {
     if (interactive()) {
-        .stop(message, r_note)
+        pa_stop(message, r_note)
     } else {
         cat(message, sep = "\n")
-        quit(status = 0)
+        quit(status = status)
     }
 }

README.rst

@@ -124,7 +124,7 @@ as well as mutually exclusive groups::
     $foo
     [1] FALSE
     > parser$parse_args(c('--foo', '--bar'))
-    Error in .stop(output, "parse error:") : parse error:
+    Error in "argparse::parse_args_output(output)" : parse error:
     usage: PROG [-h] [--foo | --bar]
     PROG: error: argument --bar: not allowed with argument --foo
 

cran-comments.rst

@@ -4,15 +4,15 @@
   Rscript) if ``parse_args()`` observes a help flag it will print a usage
   message and then call ``quit()``.  Additionally if a user specifically adds
   a 'version' argument to the command-line parser with `action='version'` then
-  if ``parse_args()`` also observes a version flag while in a non-interactive
+  if ``parse_args()`` observes a version flag while in a non-interactive
   session then it will print the version number and then call ``quit()``.
 
 * This package has a Python dependency most easily satisfied having (C)Python
   3.2 or greater on the PATH.  See file INSTALL for more details.
 
 ## Test environments
 
-* local (linux), R 4.1.3
+* local (linux), R 4.2.1
 * win-builder (windows), R devel
 * Github Actions (linux), R devel, release, oldrel
 * Github Actions (windows), R release