[ruby/irb] Support --noscript option to not use first non-option argument as script

Also add --script option to turn the option back on.

Previously there wasn't a way to get an interactive IRB session
and access arguments provided on the command line.

Additionally, handle `-` as script as stdin. In Unix-like tools, `-`
means to take standard input instead of a file.  This doesn't
result in exactly the same output for:

```
echo 'p ARGV' > args.rb; irb args.rb a b c
```

and

```
echo 'p ARGV' | irb - a b c
```

Due to how irb handles whether stdin is a tty.

However, this change allows use of `-` as a argument, instead of
giving an unrecognized switch error. This required some small
changes to context.rb (to handle `-` as standard input) and
input-method.rb (to have FileInputMethod accept IO arguments in
addition to strings).

Implements [Feature #15371]

https://github.com/ruby/irb/commit/4192683ba2

1 files changed, 4 insertions, 0 deletions

diff --git a/lib/irb/context.rb b/lib/irb/context.rb
index e6c993d423..b74cae1223 100644
--- a/lib/irb/context.rb
+++ b/lib/irb/context.rb
@@ -115,6 +115,10 @@ module IRB
         end
         @io = StdioInputMethod.new unless @io
 
+      when '-'
+        @io = FileInputMethod.new($stdin)
+        @irb_name = '-'
+        @irb_path = '-'
       when String
         @io = FileInputMethod.new(input_method)
         @irb_name = File.basename(input_method)