Allow chaining conditions in `if` using `&&`/`||`

[jprochazk]

I was surprised to find that as of v1.51, the following does not work:

arch := if os() == "macos" && arch() == "aarch64" { "arm64" } else { arch() }
print-arch:
	echo {{ arch }}

According to the GRAMMAR.md, this is not valid syntax, but only because equality cannot exist outside of an if condition.

Last mention of conditional logic I found was here: #696 - has the situation changed?

To support this, the grammar would be updated to allow equality to appear as an expression outside an if condition, and if condition would become an arbitrary expression, or only disjunct if that's too much.

  expression    : disjunct || expression
                | disjunct

- disjunct      : conjunct && disjunct
-               | conjunct
+ disjunct      : condition && disjunct
+               | condition

+ condition     : conjunct '==' conjunct
+               | conjunct '!=' conjunct
+               | conjunct '=~' conjunct
+               | conjunct

- conjunct      : 'if' condition '{' expression '}' 'else' '{' expression '}'
+ conjunct      : 'if' expression '{' expression '}' 'else' '{' expression '}'
                | 'assert' '(' condition ',' expression ')'
                | '/' expression
                | value '/' expression
                | value '+' expression
                | value

- condition     : expression '==' expression
-               | expression '!=' expression
-               | expression '=~' expression

&&/|| would have higher precedence, so a == b && c == d would parse as (a == b) && (c == d).

I'd be happy to take a stab at implementing this.

[groutoutlook]

Hi, interesting idea...

But isn't most shell already having some condition statement or operator? Like PowerShell, nutshell, fish, all somewhat modern shell implementation have those internal instructions..

It may make things more complex than it is, given we already have shell expansion or so..

Hope you can give some extra examples of this can make just recipes more comprehensive, given existed functionality can't be digested as easy as your proposal.

Regards,