Subject: Re: [PATCH] userdiff: add build-in pattern for shell

From: Junio C Hamano <[email-masked]>
Date: Wed, 29 Mar 2017 10:39:08 -0700

Ivan Tham <[email-masked]> writes:

> Shell are widely used but comes with lots of different patterns. The
> build-in pattern aim for POSIX-compatible shells with some additions:
>
> - Notably ${g//re/s} and ${g#cut}
> - "function" from bash
>
> Signed-off-by: Ivan Tham <[email-masked]>
> ---
>  Documentation/gitattributes.txt |  2 ++
>  t/t4034-diff-words.sh           |  1 +
>  t/t4034/sh/expect               | 14 ++++++++++++++
>  t/t4034/sh/post                 |  7 +++++++
>  t/t4034/sh/pre                  |  7 +++++++
>  userdiff.c                      |  5 +++++
>  6 files changed, 36 insertions(+)
>  create mode 100644 t/t4034/sh/expect
>  create mode 100644 t/t4034/sh/post
>  create mode 100644 t/t4034/sh/pre
>
> diff --git a/Documentation/gitattributes.txt b/Documentation/gitattributes.txt
> index a53d093ca..1bad72df2 100644
> --- a/Documentation/gitattributes.txt
> +++ b/Documentation/gitattributes.txt
> @@ -706,6 +706,8 @@ patterns are available:
>  
>  - `ruby` suitable for source code in the Ruby language.
>  
> +- `sh` suitable for source code in POSIX-compatible shells.

The new test you added seems to show that this is not limited to
POSIX shells but also understands bashisms like ${x//x/x}.  Perhaps
drop "POSIX-compatible" from here.

> diff --git a/userdiff.c b/userdiff.c
> index 8b732e40b..8d5127fb6 100644
> --- a/userdiff.c
> +++ b/userdiff.c
> @@ -148,6 +148,11 @@ PATTERNS("csharp",
>  	 "[a-zA-Z_][a-zA-Z0-9_]*"
>  	 "|[-+0-9.e]+[fFlL]?|0[xXbB]?[0-9a-fA-F]+[lL]?"
>  	 "|[-+*/<>%&^|=!]=|--|\\+\\+|<<=?|>>=?|&&|\\|\\||::|->"),
> +PATTERNS("sh",
> +	 "^[ \t]*(function )?[A-Za-z_][A-Za-z_0-9]*[ \t]*()[\t]*\\{?$",

There is something funky going on around parentheses on this line.
The ones around "function " is meant to be syntactic metacharacters
to produce a group in the regexp so that you can apply '?'
(i.e. zero or one occurrence) to it.  But I think the second pair of
parentheses that appears later on the line, which enclose nothing,
are meant to be literal?  E.g. "hello (){\n\techo world;\n}\n"  They
would need some quoting, perhaps like

	...[ \t]*\\(\\)[\t]*....

> +	 /* -- */
> +	 "(\\$|--?)?([a-zA-Z_][a-zA-Z0-9._]*|[0-9]+|#)|--" /* command/param */

TBH, I have no idea what this line-noise is doing.

$foobar, $4, --foobar, foobar, 123 and -- can be seen easily out of
these patterns.  I am not sure what --# would be (perhaps you meant
to only catch $# and --# is included by accident, in which case it
is understandable).  It feels a bit strange to see that $# is
supported but not $?; --foo but not --foo=bar; foobar but not "foo
bar" inside a dq-pair.

> +	 "|\\$[({]|[)}]|[-+*/=!]=?|[\\]&%#/|]{1,2}|[<>]{1,3}|[ \t]#.*"),

And this one is even more dense.