From dd1c805949b5996a79adeb690cc0d468e2d88836 Mon Sep 17 00:00:00 2001
From: Elizabeth Mattijsen <liz@wenzperl.nl>
Date: Fri, 22 Mar 2019 17:43:44 +0100
Subject: [PATCH] Simplify candidate selection in MAIN usage

A recent change tried to be smarter on which MAIN candidates to show.  This
was however too smart for its own good, omitting candidates when it shouldn't.
Now limiting of candidates will only happen if the first given parameter
matches a **constant** value as the first parameter.  So if you have multiple
MAIN candidates that have "foo" as the first parameter, and you give "foo"
as the first command line argument, then only those candidates will be
selected for the usage message if no appropriate candidate was found for
execution.  In all other cases, all candidates will be shown if no candidate
was found for execution.

Spotted at Andrew Shitov's talk at the German Perl Workshop.
---
 src/core/Main.pm6 | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/src/core/Main.pm6 b/src/core/Main.pm6
index bd0e0fef97d..3bf55a00106 100644
--- a/src/core/Main.pm6
+++ b/src/core/Main.pm6
@@ -127,25 +127,18 @@ my sub RUN-MAIN(&main, $mainline, :$in-as-argsfiles) {
 
         # Select candidates for which to create USAGE string
         sub usage-candidates($capture) {
-            my @candidates = &main.candidates;
-            my @positionals = $capture.list;
-
-            my @candos;
-            while @positionals && !@candos {
-
-                # Find candidates on which all these positionals match
-                @candos = @candidates.grep: -> $sub {
-                    my @params = $sub.signature.params;
-                    if @positionals <= @params {
-                        (^@positionals).first( -> int $i {
-                            !(@params[$i].constraints.ACCEPTS(@positionals[$i]))
-                        } ).defined.not
+            my @candidates = &main.candidates.grep: { !.?is-hidden-from-USAGE }
+            if $capture.list -> @positionals {
+                my $first := @positionals[0];
+                if @candidates.grep: -> $sub {
+                    if $sub.signature.params[0].cool_constant -> $literal {
+                       $literal.ACCEPTS($first)
                     }
+                } -> @candos {
+                    return @candos;
                 }
-                @positionals.pop;
             }
-            (@candos || @candidates)
-              .grep: { nqp::not_i(nqp::can($_,'is-hidden-from-USAGE')) }
+            @candidates
         }
 
         for usage-candidates(capture) -> $sub {