use dynamic precedence to fix 'is' and allow not not

CLAUDE.md

@@ -79,7 +79,11 @@ Consequences worth knowing before editing a rule:
   fail at generate time; it shows up as `MISSING` nodes in a passing-looking parse.
 - **`conflicts` entries are the normal fix, not precedence.** With explicit separators the lookahead at a
   part boundary is `SEP` instead of the meaningful token, so LR(1) loses its discriminator. That is why
-  `predicate` and `[$.library, $.load]` are listed there.
+  `predicate`, `binaryOperator` and `[$.library, $.load]` are listed there. Where two readings both stay
+  valid to the end — `is not` as one operator or as `is` and a prefix `not` — the conflict needs a
+  `prec.dynamic` alongside it to settle which wins; a static `prec` resolves the shift/reduce while the
+  table is built and discards the other parse outright, which is how a bare `{% if x is y %}` came to be
+  an error.
 
 ### A tag group is a sequence of clauses
 

grammar.js

@@ -359,6 +359,7 @@ const django = grammar({
     [$.timezone_clause],
     [$.with_clause],
     [$.predicate],
+    [$.binaryOperator],
     [$.library, $.load],
     [$._translate_option],
     [$._filtered_value_spaced],
@@ -426,18 +427,18 @@ const django = grammar({
         "<=",
         ">=",
         "in",
-        prec(1, joined("not", "in")),
+        prec.dynamic(1, joined("not", "in")),
         "is",
-        prec(1, joined("is", "not")),
+        prec.dynamic(1, joined("is", "not")),
       ),
     predicate: ($) =>
       seq(
-        optional(seq("not", SEP)),
+        repeat(seq("not", SEP)),
         $.filtered_value,
         repeat(
           seq(
             part($.binaryOperator),
-            optional(part("not")),
+            repeat(part("not")),
             part($.filtered_value),
           ),
         ),

src/grammar.json

@@ -493,7 +493,7 @@
           "value": "in"
         },
         {
-          "type": "PREC",
+          "type": "PREC_DYNAMIC",
           "value": 1,
           "content": {
             "type": "SEQ",
@@ -518,7 +518,7 @@
           "value": "is"
         },
         {
-          "type": "PREC",
+          "type": "PREC_DYNAMIC",
           "value": 1,
           "content": {
             "type": "SEQ",
@@ -544,25 +544,20 @@
       "type": "SEQ",
       "members": [
         {
-          "type": "CHOICE",
+          "type": "REPEAT",
-          "members": [
+          "content": {
-            {
+            "type": "SEQ",
-              "type": "SEQ",
+            "members": [
-              "members": [
+              {
-                {
+                "type": "STRING",
-                  "type": "STRING",
+                "value": "not"
-                  "value": "not"
+              },
-                },
+              {
-                {
+                "type": "PATTERN",
-                  "type": "PATTERN",
+                "value": "[ \\t\\r\\n]+"
-                  "value": "[ \\t\\r\\n]+"
+              }
-                }
+            ]
-              ]
+          }
-            },
-            {
-              "type": "BLANK"
-            }
-          ]
         },
         {
           "type": "SYMBOL",
@@ -587,25 +582,20 @@
                 ]
               },
               {
-                "type": "CHOICE",
+                "type": "REPEAT",
-                "members": [
+                "content": {
-                  {
+                  "type": "SEQ",
-                    "type": "SEQ",
+                  "members": [
-                    "members": [
+                    {
-                      {
+                      "type": "PATTERN",
-                        "type": "PATTERN",
+                      "value": "[ \\t\\r\\n]+"
-                        "value": "[ \\t\\r\\n]+"
+                    },
-                      },
+                    {
-                      {
+                      "type": "STRING",
-                        "type": "STRING",
+                      "value": "not"
-                        "value": "not"
+                    }
-                      }
+                  ]
-                    ]
+                }
-                  },
-                  {
-                    "type": "BLANK"
-                  }
-                ]
               },
               {
                 "type": "SEQ",
@@ -8598,6 +8588,9 @@
     [
       "predicate"
     ],
+    [
+      "binaryOperator"
+    ],
     [
       "library",
       "load"

test/corpus/if.txt

@@ -182,3 +182,149 @@ If Is Not None
       (template
         (content))))
   (content))
+
+==================
+If Is
+==================
+
+{% if x is y %}a{% endif %}
+
+---
+
+(template
+  (content)
+  (if_group
+    (if_clause
+      (predicate
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier))))
+        (binaryOperator)
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier)))))
+      (template
+        (content))))
+  (content))
+
+==================
+If Is Not
+==================
+
+{% if x is not y %}a{% endif %}
+
+---
+
+(template
+  (content)
+  (if_group
+    (if_clause
+      (predicate
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier))))
+        (binaryOperator)
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier)))))
+      (template
+        (content))))
+  (content))
+
+==================
+If Is Not Not
+==================
+
+{% if x is not not y %}a{% endif %}
+
+---
+
+(template
+  (content)
+  (if_group
+    (if_clause
+      (predicate
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier))))
+        (binaryOperator)
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier)))))
+      (template
+        (content))))
+  (content))
+
+==================
+If With A Repeated Not
+==================
+
+{% if not not x %}a{% endif %}
+
+---
+
+(template
+  (content)
+  (if_group
+    (if_clause
+      (predicate
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier)))))
+      (template
+        (content))))
+  (content))
+
+==================
+If Not Before A Name Beginning With In
+==================
+
+{% if not in_stock %}a{% endif %}
+
+---
+
+(template
+  (content)
+  (if_group
+    (if_clause
+      (predicate
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier)))))
+      (template
+        (content))))
+  (content))
+
+==================
+If Is Before A Name Beginning With Not
+==================
+
+{% if x is nothing %}a{% endif %}
+
+---
+
+(template
+  (content)
+  (if_group
+    (if_clause
+      (predicate
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier))))
+        (binaryOperator)
+        (filtered_value
+          (value
+            (variable_attribute
+              (identifier)))))
+      (template
+        (content))))
+  (content))