From c25fa9910ecfb07f92a37fb2faef70d418ec6781 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Thu, 25 Feb 2021 21:41:35 -0800
Subject: [PATCH] Fix query match failure when indefinite steps have no
 captures

Fixes #937
---
 cli/src/tests/query_test.rs | 50 +++++++++++++++++++++++++++++++++++++
 lib/src/query.c             |  2 +-
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/cli/src/tests/query_test.rs b/cli/src/tests/query_test.rs
index 37e13f05..8a44af3c 100644
--- a/cli/src/tests/query_test.rs
+++ b/cli/src/tests/query_test.rs
@@ -1861,6 +1861,56 @@ fn test_query_matches_with_repeated_fields() {
     });
 }
 
+#[test]
+fn test_query_matches_with_indefinite_step_containing_no_captures() {
+    allocations::record(|| {
+        // This pattern depends on the field declarations within the
+        // struct's body, but doesn't capture anything within the body.
+        // It demonstrates that internally, state-splitting needs to occur
+        // for each field declaration within the body, in order to avoid
+        // prematurely failing if the first field does not match.
+        //
+        // https://github.com/tree-sitter/tree-sitter/issues/937
+        let language = get_language("c");
+        let query = Query::new(
+            language,
+            "(struct_specifier
+                name: (type_identifier) @name
+                body: (field_declaration_list
+                    (field_declaration
+                        type: (union_specifier))))",
+        )
+        .unwrap();
+
+        assert_query_matches(
+            language,
+            &query,
+            "
+            struct LacksUnionField {
+                int a;
+                struct {
+                    B c;
+                } d;
+                G *h;
+            };
+
+            struct HasUnionField {
+                int a;
+                struct {
+                    B c;
+                } d;
+                union {
+                    bool e;
+                    float f;
+                } g;
+                G *h;
+            };
+            ",
+            &[(0, vec![("name", "HasUnionField")])],
+        );
+    });
+}
+
 #[test]
 fn test_query_captures_basic() {
     allocations::record(|| {
diff --git a/lib/src/query.c b/lib/src/query.c
index 247880c7..d28e1b92 100644
--- a/lib/src/query.c
+++ b/lib/src/query.c
@@ -2676,7 +2676,7 @@ static inline bool ts_query_cursor__advance(
         // parent, then this query state cannot simply be updated in place. It must be
         // split into two states: one that matches this node, and one which skips over
         // this node, to preserve the possibility of matching later siblings.
-        if (later_sibling_can_match && step->contains_captures) {
+        if (later_sibling_can_match && (step->contains_captures || !step->is_definite)) {
           if (ts_query_cursor__copy_state(self, &state)) {
             LOG(
               "  split state for capture. pattern:%u, step:%u\n",