Python: Allow use of match as an identifier

This previously only worked in certain circumstances. In particular,
assignments such as `match[1] = ...` or even just `match[1]` would fail
to parse correctly.

Fixing this turned out to be less trivial than anticipated. Consider the
fact that
```
match [1]: case (...)
```
can either look the start of a `match` statement, or it could be a type
ascription, ascribing the value of `case(...)` (a call) to the item at
index 1 of `match`.

To fix this, then, we give `match` the identifier and `match` the
statement the same precendence in the grammar, and additionally also
mark a conflict between `match_statement` and `primary_expression`. This
causes the conflict to be resolved dynamically, and seems to do the
right thing in all cases.

Author: tausbn

python/extractor/tests/parser/soft_keywords_new.expected

@@ -0,0 +1,137 @@
+Module: [1, 0] - [21, 0]
+  body: [
+    Expr: [1, 0] - [1, 8]
+      value:
+        Subscript: [1, 0] - [1, 8]
+          value:
+            Name: [1, 0] - [1, 5]
+              variable: Variable('match', None)
+              ctx: Load
+          index:
+            Num: [1, 6] - [1, 7]
+              n: 1
+              text: '1'
+          ctx: Load
+    Assign: [2, 0] - [2, 12]
+      targets: [
+        Subscript: [2, 0] - [2, 8]
+          value:
+            Name: [2, 0] - [2, 5]
+              variable: Variable('match', None)
+              ctx: Load
+          index:
+            Num: [2, 6] - [2, 7]
+              n: 2
+              text: '2'
+          ctx: Store
+      ]
+      value:
+        Num: [2, 11] - [2, 12]
+          n: 3
+          text: '3'
+    Assign: [4, 0] - [4, 13]
+      targets: [
+        Attribute: [4, 0] - [4, 9]
+          value:
+            Name: [4, 0] - [4, 5]
+              variable: Variable('match', None)
+              ctx: Load
+          attr: 'foo'
+          ctx: Store
+      ]
+      value:
+        Num: [4, 12] - [4, 13]
+          n: 4
+          text: '4'
+    Expr: [6, 0] - [6, 7]
+      value:
+        Call: [6, 0] - [6, 7]
+          func:
+            Name: [6, 0] - [6, 5]
+              variable: Variable('match', None)
+              ctx: Load
+          positional_args: []
+          named_args: []
+    AnnAssign: [8, 0] - [8, 15]
+      value: None
+      annotation:
+        Name: [8, 11] - [8, 15]
+          variable: Variable('case', None)
+          ctx: Load
+      target:
+        Subscript: [8, 0] - [8, 8]
+          value:
+            Name: [8, 0] - [8, 5]
+              variable: Variable('match', None)
+              ctx: Load
+          index:
+            Num: [8, 6] - [8, 7]
+              n: 5
+              text: '5'
+          ctx: Store
+    Match: [12, 0] - [14, 12]
+      subject:
+        List: [12, 6] - [12, 9]
+          elts: [
+            Num: [12, 7] - [12, 8]
+              n: 6
+              text: '6'
+          ]
+          ctx: Load
+      cases: [
+        Case: [13, 4] - [14, 12]
+          pattern:
+            MatchLiteralPattern: [13, 9] - [13, 10]
+              literal:
+                Num: [13, 9] - [13, 10]
+                  n: 7
+                  text: '7'
+          guard: None
+          body: [
+            Pass: [14, 8] - [14, 12]
+          ]
+      ]
+    Print: [17, 0] - [17, 19]
+      dest:
+        Num: [17, 9] - [17, 10]
+          n: 8
+          text: '8'
+      values: [
+        Str: [17, 12] - [17, 19]
+          s: 'hello'
+          prefix: '"'
+          implicitly_concatenated_parts: None
+      ]
+      nl: True
+    Expr: [18, 0] - [18, 19]
+      value:
+        Tuple: [18, 0] - [18, 19]
+          elts: [
+            BinOp: [18, 0] - [18, 10]
+              left:
+                Name: [18, 0] - [18, 5]
+                  variable: Variable('pront', None)
+                  ctx: Load
+              op: RShift
+              right:
+                Num: [18, 9] - [18, 10]
+                  n: 9
+                  text: '9'
+            Str: [18, 12] - [18, 19]
+              s: 'world'
+              prefix: '"'
+              implicitly_concatenated_parts: None
+          ]
+          ctx: Load
+    Expr: [20, 0] - [20, 10]
+      value:
+        Await: [20, 0] - [20, 10]
+          value:
+            List: [20, 6] - [20, 10]
+              elts: [
+                Num: [20, 7] - [20, 9]
+                  n: 10
+                  text: '10'
+              ]
+              ctx: Load
+  ]

python/extractor/tests/parser/soft_keywords_new.py

@@ -0,0 +1,20 @@
+match[1]
+match[2] = 3
+
+match.foo = 4
+
+match()
+
+match[5] : case
+
+
+# match used "properly"
+match [6]:
+    case 7:
+        pass
+
+
+print >> 8, "hello" # Python 2-style print
+pront >> 9, "world" # How this would be interpreted in Python 3
+
+await [10] # In Python 2 this would be an indexing operation, but it's more likely to be an await.

python/extractor/tsg-python/tsp/grammar.js

@@ -36,6 +36,7 @@ module.exports = grammar({
     [$.tuple, $.tuple_pattern],
     [$.list, $.list_pattern],
     [$.with_item, $._collection_elements],
+    [$.match_statement, $.primary_expression],
   ],
 
   supertypes: $ => [
@@ -349,7 +350,7 @@ module.exports = grammar({
       ))
     )),
 
-    match_statement: $ => seq(
+    match_statement: $ => prec(-3, seq(
       'match',
       field('subject',
         choice(
@@ -359,7 +360,7 @@ module.exports = grammar({
       ),
       ':',
       field('cases', $.cases)
-    ),
+    )),
 
     cases: $ => repeat1($.case_block),