From 5fa28ce015a595ba8042be58a951b2f2a83eef10 Mon Sep 17 00:00:00 2001
From: Koichi ITO <koic.ito@gmail.com>
Date: Wed, 13 Mar 2024 10:46:10 +0900
Subject: [PATCH] [ruby/prism] Warn `&` interpreted as argument prefix

This PR makes `Prism` warn `&` interpreted as argument prefix.
This carries a similar meaning to the following Ruby warning:

```console
$ ruby -cwe "foo &bar"
-e:1: warning: `&' interpreted as argument prefix
Syntax OK
```

Previously, it did not issue a warning:

```console
$ bundle exec ruby -rprism -ve "p Prism.parse('foo &bar').warnings"
ruby 3.3.0 (2023-12-25 revision https://github.com/ruby/prism/commit/5124f9ac75) [x86_64-darwin22]
[]
```

From now on, it will issue a warning similar to Ruby's:

```console
$ bundle exec ruby -rprism -ve "p Prism.parse('foo &bar').warnings"
ruby 3.3.0 (2023-12-25 revision https://github.com/ruby/prism/commit/5124f9ac75) [x86_64-darwin22]
[#<Prism::ParseWarning @type=:ambiguous_prefix_amp @message="ambiguous `&` has been interpreted as an argument prefix"
@location=#<Prism::Location @start_offset=4 @length=1 start_line=1> @level=:verbose>]
```

https://github.com/ruby/prism/commit/312f99cd1e
---
 prism/config.yml                     | 1 +
 prism/prism.c                        | 5 ++++-
 prism/templates/src/diagnostic.c.erb | 1 +
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/prism/config.yml b/prism/config.yml
index e395c5a8c3..f7dcc1f79f 100644
--- a/prism/config.yml
+++ b/prism/config.yml
@@ -233,6 +233,7 @@ errors:
 warnings:
   - AMBIGUOUS_FIRST_ARGUMENT_MINUS
   - AMBIGUOUS_FIRST_ARGUMENT_PLUS
+  - AMBIGUOUS_PREFIX_AMPERSAND
   - AMBIGUOUS_PREFIX_STAR
   - AMBIGUOUS_PREFIX_STAR_STAR
   - AMBIGUOUS_SLASH
diff --git a/prism/prism.c b/prism/prism.c
index 95ac872bb2..947d1a92bb 100644
--- a/prism/prism.c
+++ b/prism/prism.c
@@ -9912,7 +9912,10 @@ parser_lex(pm_parser_t *parser) {
                     }
 
                     pm_token_type_t type = PM_TOKEN_AMPERSAND;
-                    if (lex_state_spcarg_p(parser, space_seen) || lex_state_beg_p(parser)) {
+                    if (lex_state_spcarg_p(parser, space_seen)) {
+                        pm_parser_warn_token(parser, &parser->current, PM_WARN_AMBIGUOUS_PREFIX_AMPERSAND);
+                        type = PM_TOKEN_UAMPERSAND;
+                    } else if (lex_state_beg_p(parser)) {
                         type = PM_TOKEN_UAMPERSAND;
                     }
 
diff --git a/prism/templates/src/diagnostic.c.erb b/prism/templates/src/diagnostic.c.erb
index 8ca5cff3e8..5ba4d62317 100644
--- a/prism/templates/src/diagnostic.c.erb
+++ b/prism/templates/src/diagnostic.c.erb
@@ -313,6 +313,7 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     // Warnings
     [PM_WARN_AMBIGUOUS_FIRST_ARGUMENT_MINUS]    = { "ambiguous first argument; put parentheses or a space even after `-` operator", PM_WARNING_LEVEL_VERBOSE },
     [PM_WARN_AMBIGUOUS_FIRST_ARGUMENT_PLUS]     = { "ambiguous first argument; put parentheses or a space even after `+` operator", PM_WARNING_LEVEL_VERBOSE },
+    [PM_WARN_AMBIGUOUS_PREFIX_AMPERSAND]        = { "ambiguous `&` has been interpreted as an argument prefix", PM_WARNING_LEVEL_VERBOSE },
     [PM_WARN_AMBIGUOUS_PREFIX_STAR]             = { "ambiguous `*` has been interpreted as an argument prefix", PM_WARNING_LEVEL_VERBOSE },
     [PM_WARN_AMBIGUOUS_PREFIX_STAR_STAR]        = { "ambiguous `**` has been interpreted as an argument prefix", PM_WARNING_LEVEL_VERBOSE },
     [PM_WARN_AMBIGUOUS_SLASH]                   = { "ambiguous `/`; wrap regexp in parentheses or add a space after `/` operator", PM_WARNING_LEVEL_VERBOSE },