black/parser: partial support for pattern matching (#2586)

[etc/vim.git] / src / blib2to3 / Grammar.txt

diff --git a/src/blib2to3/Grammar.txt b/src/blib2to3/Grammar.txt
index 69b9af966086b5bb18282042e2053efdaf002a21..49680323d8b8fe83c98bee1940ee4e1d1e1f94d1 100644 (file)
--- a/src/blib2to3/Grammar.txt
+++ b/src/blib2to3/Grammar.txt
@@ -105,7 +105,7 @@ global_stmt: ('global' | 'nonlocal') NAME (',' NAME)*
 exec_stmt: 'exec' expr ['in' test [',' test]]
 assert_stmt: 'assert' test [',' test]
 
-compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated | async_stmt
+compound_stmt: if_stmt | while_stmt | for_stmt | try_stmt | with_stmt | funcdef | classdef | decorated | async_stmt | match_stmt
 async_stmt: ASYNC (funcdef | with_stmt | for_stmt)
 if_stmt: 'if' namedexpr_test ':' suite ('elif' namedexpr_test ':' suite)* ['else' ':' suite]
 while_stmt: 'while' namedexpr_test ':' suite ['else' ':' suite]
@@ -115,9 +115,8 @@ try_stmt: ('try' ':' suite
            ['else' ':' suite]
            ['finally' ':' suite] |
           'finally' ':' suite))
-with_stmt: 'with' with_item (',' with_item)*  ':' suite
-with_item: test ['as' expr]
-with_var: 'as' expr
+with_stmt: 'with' asexpr_test (',' asexpr_test)*  ':' suite
+
 # NB compile.c makes sure that the default except clause is last
 except_clause: 'except' [test [(',' | 'as') test]]
 suite: simple_stmt | NEWLINE INDENT stmt+ DEDENT
@@ -131,7 +130,15 @@ testlist_safe: old_test [(',' old_test)+ [',']]
 old_test: or_test | old_lambdef
 old_lambdef: 'lambda' [varargslist] ':' old_test
 
-namedexpr_test: test [':=' test]
+namedexpr_test: asexpr_test [':=' asexpr_test]
+
+# This is actually not a real rule, though since the parser is very
+# limited in terms of the strategy about match/case rules, we are inserting
+# a virtual case (<expr> as <expr>) as a valid expression. Unless a better
+# approach is thought, the only side effect of this seem to be just allowing
+# more stuff to be parser (which would fail on the ast).
+asexpr_test: test ['as' test]
+
 test: or_test ['if' or_test 'else' test] | lambdef
 or_test: and_test ('or' and_test)*
 and_test: not_test ('and' not_test)*
@@ -157,14 +164,14 @@ testlist_gexp: (namedexpr_test|star_expr) ( old_comp_for | (',' (namedexpr_test|
 lambdef: 'lambda' [varargslist] ':' test
 trailer: '(' [arglist] ')' | '[' subscriptlist ']' | '.' NAME
 subscriptlist: subscript (',' subscript)* [',']
-subscript: test | [test] ':' [test] [sliceop]
+subscript: test [':=' test] | [test] ':' [test] [sliceop]
 sliceop: ':' [test]
 exprlist: (expr|star_expr) (',' (expr|star_expr))* [',']
 testlist: test (',' test)* [',']
 dictsetmaker: ( ((test ':' test | '**' expr)
                  (comp_for | (',' (test ':' test | '**' expr))* [','])) |
-                ((test | star_expr)
-                (comp_for | (',' (test | star_expr))* [','])) )
+                ((test [':=' test] | star_expr)
+                (comp_for | (',' (test [':=' test] | star_expr))* [','])) )
 
 classdef: 'class' NAME ['(' [arglist] ')'] ':' suite
 
@@ -213,3 +220,27 @@ encoding_decl: NAME
 
 yield_expr: 'yield' [yield_arg]
 yield_arg: 'from' test | testlist_star_expr
+
+
+# 3.10 match statement definition
+
+# PS: normally the grammar is much much more restricted, but
+# at this moment for not trying to bother much with encoding the
+# exact same DSL in a LL(1) parser, we will just accept an expression
+# and let the ast.parse() step of the safe mode to reject invalid
+# grammar.
+
+# The reason why it is more restricted is that, patterns are some
+# sort of a DSL (more advanced than our LHS on assignments, but
+# still in a very limited python subset). They are not really
+# expressions, but who cares. If we can parse them, that is enough
+# to reformat them.
+
+match_stmt: "match" subject_expr ':' NEWLINE INDENT case_block+ DEDENT
+subject_expr: namedexpr_test
+
+# cases
+case_block: "case" patterns [guard] ':' suite
+guard: 'if' namedexpr_test
+patterns: pattern ['as' pattern]
+pattern: (expr|star_expr) (',' (expr|star_expr))* [',']