Distinguish unset commands from regular commands

corpus/expressions.txt

@@ -265,83 +265,6 @@ echo "#"
   (command (command_name (word)) (string))
   (command (command_name (word)) (string)))
 
-=========================================
-Variable declaration: declare & typeset
-=========================================
-
-declare var1
-typeset -i -r var2=42 var3=10
-
----
-
-(program
-  (declaration_command (variable_name))
-  (declaration_command (word) (word)
-    (variable_assignment (variable_name) (word))
-    (variable_assignment (variable_name) (word))))
-
-=========================================
-Variable declaration: readonly
-=========================================
-
-readonly var1
-readonly var2=42
-
----
-
-(program
-  (declaration_command (variable_name))
-  (declaration_command (variable_assignment (variable_name) (word))))
-
-=========================================
-Variable declaration: local
-=========================================
-
-local a=42 b
-local -r c
-
----
-
-(program
-  (declaration_command
-    (variable_assignment (variable_name) (word))
-    (variable_name))
-  (declaration_command
-    (word)
-    (variable_name)))
-
-=========================================
-Variable declaration: export
-=========================================
-
-export PATH
-export FOOBAR PATH="$PATH:/usr/foobar/bin"
-
----
-
-(program
-  (declaration_command (variable_name))
-  (declaration_command
-    (variable_name)
-    (variable_assignment (variable_name) (string (simple_expansion (variable_name))))))
-
-===========================================
-Expressions passed to declaration commands
-===========================================
-
-export "$(echo ${key} | tr [:lower:] [:upper:])=${p_key#*=}"
-
----
-
-(program
-  (declaration_command
-    (string
-      (command_substitution
-        (pipeline
-          (command (command_name (word)) (expansion (variable_name)))
-          (command (command_name (word)) (concatenation (word)) (concatenation (word)))))
-      (expansion (variable_name) (word)))))
-
 =========================================
 Arrays and array expansions
 =========================================

corpus/statements.txt

@@ -171,3 +171,95 @@ function do_yet_another_thing {
     (word)
     (compound_statement (command (command_name (word)) (word)))
     (file_redirect (file_descriptor) (word))))
+
+=========================================
+Variable declaration: declare & typeset
+=========================================
+
+declare var1
+typeset -i -r var2=42 var3=10
+
+---
+
+(program
+  (declaration_command (variable_name))
+  (declaration_command (word) (word)
+    (variable_assignment (variable_name) (word))
+    (variable_assignment (variable_name) (word))))
+
+=========================================
+Variable declaration: readonly
+=========================================
+
+readonly var1
+readonly var2=42
+
+---
+
+(program
+  (declaration_command (variable_name))
+  (declaration_command (variable_assignment (variable_name) (word))))
+
+=========================================
+Variable declaration: local
+=========================================
+
+local a=42 b
+local -r c
+
+---
+
+(program
+  (declaration_command
+    (variable_assignment (variable_name) (word))
+    (variable_name))
+  (declaration_command
+    (word)
+    (variable_name)))
+
+=========================================
+Variable declaration: export
+=========================================
+
+export PATH
+export FOOBAR PATH="$PATH:/usr/foobar/bin"
+
+---
+
+(program
+  (declaration_command (variable_name))
+  (declaration_command
+    (variable_name)
+    (variable_assignment (variable_name) (string (simple_expansion (variable_name))))))
+
+===========================================
+Expressions passed to declaration commands
+===========================================
+
+export "$(echo ${key} | tr [:lower:] [:upper:])=${p_key#*=}"
+
+---
+
+(program
+  (declaration_command
+    (string
+      (command_substitution
+        (pipeline
+          (command (command_name (word)) (expansion (variable_name)))
+          (command (command_name (word)) (concatenation (word)) (concatenation (word)))))
+      (expansion (variable_name) (word)))))
+
+=========================================
+Unset commands
+=========================================
+
+unset A
+unset "$variable_name"
+unsetenv -f ONE TWO
+
+---
+
+(program
+  (unset_command (variable_name))
+  (unset_command (string (simple_expansion (variable_name))))
+  (unset_command (word) (variable_name) (variable_name)))

grammar.js

@@ -56,6 +56,7 @@ module.exports = grammar({
       $.variable_assignment,
       $.command,
       $.declaration_command,
+      $.unset_command,
       $.bracket_command,
       $.for_statement,
       $.while_statement,
@@ -229,6 +230,14 @@ module.exports = grammar({
       ))
     )),
 
+    unset_command: $ => prec.left(seq(
+      choice('unset', 'unsetenv'),
+      repeat(choice(
+        $._expression,
+        $._simple_variable_name
+      ))
+    )),
+
     _assignment: $ => seq(
       choice(
         '=',

src/grammar.json

@@ -36,6 +36,10 @@
           "type": "SYMBOL",
           "name": "declaration_command"
         },
+        {
+          "type": "SYMBOL",
+          "name": "unset_command"
+        },
         {
           "type": "SYMBOL",
           "name": "bracket_command"
@@ -832,6 +836,44 @@
         ]
       }
     },
+    "unset_command": {
+      "type": "PREC_LEFT",
+      "value": 0,
+      "content": {
+        "type": "SEQ",
+        "members": [
+          {
+            "type": "CHOICE",
+            "members": [
+              {
+                "type": "STRING",
+                "value": "unset"
+              },
+              {
+                "type": "STRING",
+                "value": "unsetenv"
+              }
+            ]
+          },
+          {
+            "type": "REPEAT",
+            "content": {
+              "type": "CHOICE",
+              "members": [
+                {
+                  "type": "SYMBOL",
+                  "name": "_expression"
+                },
+                {
+                  "type": "SYMBOL",
+                  "name": "_simple_variable_name"
+                }
+              ]
+            }
+          }
+        ]
+      }
+    },
     "_assignment": {
       "type": "SEQ",
       "members": [