Support for PEP 622 structural pattern matching

[wbadart]

Hey team- just wanted to start the discussion about PEP 622 since it introduces some new syntax. Any thoughts on what the effort might be to add support? I'm guessing adding the match and case keywords will get us pretty far (and I'd be happy to take a stab at this) but I'd also want to get ahead of any hairy corner cases in the new syntax (e.g. guards, or patterns, ...).

Thanks for your consideration!

[kfollstad]

Hi @wbadart,

I found this repo looking for exactly that, highlighting for current syntax, so thanks for bringing this and the ModuleNotFoundError up.

For what it is worth, what I notice is that the existing syntax file makes no attempt to perform nextgroup checking for other keywords aside from raise, def, and class. The more complicated cases where an elaborate python expression follows such as for if, elif, else, try, except, etc are implemented as just straight keywords with no additional checking. Consequently I don't see why taking the same approach when the case patterns / guards that follow also get quite complicated would not at the least be a great starting point.

[char101]

Basic support for match/case

diff --git a/syntax/python.vim b/syntax/python.vim
index 2524aba..3d49f51 100644
--- a/syntax/python.vim
+++ b/syntax/python.vim
@@ -81,6 +81,7 @@ if s:Enabled('g:python_highlight_class_vars')
 endif
 syn keyword pythonRepeat for while
 syn keyword pythonConditional if elif else
+syn keyword pythonMatch match case
 syn keyword pythonException try except finally
 " The standard pyrex.vim unconditionally removes the pythonInclude group, so
 " we provide a dummy group here to avoid crashing pyrex.vim.
@@ -105,7 +106,7 @@ else
 syn match pythonStatement '\<async\s\+def\>' nextgroup=pythonFunction skipwhite
 syn match pythonStatement '\<async\s\+with\>'
 syn match pythonStatement '\<async\s\+for\>'
- syn cluster pythonExpression contains=pythonStatement,pythonRepeat,pythonConditional,pythonOperator,pythonNumber,pythonHexNumber,pythonOctNumber,pythonBinNumber,pythonFloat,pythonString,pythonFString,pythonRawString,pythonRawFString,pythonBytes,pythonBoolean,pythonNone,pythonSingleton,pythonBuiltinObj,pythonBuiltinFunc,pythonBuiltinType,pythonClassVar
+ syn cluster pythonExpression contains=pythonStatement,pythonRepeat,pythonConditional,pythonMatch,pythonOperator,pythonNumber,pythonHexNumber,pythonOctNumber,pythonBinNumber,pythonFloat,pythonString,pythonFString,pythonRawString,pythonRawFString,pythonBytes,pythonBoolean,pythonNone,pythonSingleton,pythonBuiltinObj,pythonBuiltinFunc,pythonBuiltinType,pythonClassVar
 endif


@@ -434,6 +435,7 @@ if v:version >= 508 || !exists('did_python_syn_inits')
 HiLink pythonFunction Function
 HiLink pythonFunctionCall Function
 HiLink pythonConditional Conditional
+ HiLink pythonMatch Conditional
 HiLink pythonRepeat Repeat
 HiLink pythonException Exception
 HiLink pythonOperator Operator

[GBeauregard]

This is presumably harder than it seems since the new keywords are "soft" and only keywords in certain contexts.

[char101]

So match and case can be variable/function/class name outside match expression. Can match pattern have higher priorities? We can make those syntax have higher priorities than match/case syntax.

[GBeauregard]

Yeah, and _ is a soft keyword too. See python/cpython#25851 for what IDLE did.