From: merch-redmine@...
Date: 2020-11-15T06:11:24+00:00
Subject: [ruby-core:100855] [Ruby master Bug#17124] Wrong "ambiguous first	argument" warning

Issue #17124 has been updated by jeremyevans0 (Jeremy Evans).

Status changed from Open to Feedback

marcandre (Marc-Andre Lafortune) wrote in #note-3:
> I hadn't thought of `method /a /x` or `method /a /<newline>other_method`, indeed.
> 
> This warning is only there when there is ambiguity between two divisions and a regexp literal, right?

No, the warning is used for `+` and `-` in addition to `/`.

> If so, could we reword the warning to "ambiguity between regexp and two divisions: wrap regexp in parentheses or add a space after `/' operator"?

This requires treating the `/` operator differently than `+` and `-` in terms of the warning.  Do you think the benefit is worth the cost?

```diff
--- a/parse.y
+++ b/parse.y
@@ -7788,7 +7788,12 @@ static int
 arg_ambiguous(struct parser_params *p, char c)
 {
 #ifndef RIPPER
-    rb_warning1("ambiguous first argument; put parentheses or a space even after `%c' operator", WARN_I(c));
+    if (c == '/') {
+        rb_warning1("ambiguity between regexp and two divisions: wrap regexp in parentheses or add a space after `%c' operator", WARN_I(c));
+    }
+    else {
+        rb_warning1("ambiguous first argument; put parentheses or a space even after `%c' operator", WARN_I(c));
+    }
 #else
     dispatch1(arg_ambiguous, rb_usascii_str_new(&c, 1));
 #endif
```

----------------------------------------
Bug #17124: Wrong "ambiguous first argument" warning
https://bugs.ruby-lang.org/issues/17124#change-88500

* Author: marcandre (Marc-Andre Lafortune)
* Status: Feedback
* Priority: Normal
* Assignee: nobu (Nobuyoshi Nakada)
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
```sh
$ ruby -v -e "x='a'; x.match? /[a-z]/"
ruby 2.8.0dev (2020-07-30T14:07:06Z master 352895b751) [x86_64-darwin18]
-e:1: warning: ambiguous first argument; put parentheses or a space even after `/' operator
```

There is no `/` operator in there and there is also no ambiguity as adding a space after the first `/` is a syntax error.

Is it possible to remove the warning altogether when the argument is lexed as a regexp?

The message could use a rewording too, maybe "ambiguous first argument; put parentheses around argument or add a space after `/' operator"



-- 
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