add missing tag marker and error query

queries/errors.scm

@@ -0,0 +1,42 @@
+; Everything in a template that an editor should report as a problem.
+;
+; A group whose required tag is missing parses without an ERROR: the scanner
+; supplies a zero-width marker where the tag belongs, so the group, its clauses
+; and the scopes they open stay intact for completion and the other queries.
+; Such a tree has no error of its own (ts_node_has_error is false), so a tool
+; has to run this query to find them.
+;
+;   @error.syntax       input the grammar could not parse
+;   @error.missing      a token that tree-sitter's error recovery inserted
+;   @error.missing_tag  a tag its group requires, absent where the marker is;
+;                       the marker's type names the tag
+;
+; The markers are listed one by one, as MISSING_BLOCKS in grammar.js: the
+; generator drops a supertype whose members are aliases, so there is no single
+; node type to match them all. A new tag group, or a new kind of marker, is
+; added here.
+
+(ERROR) @error.syntax
+
+(MISSING) @error.missing
+
+[
+    (missing_endautoescape_block)
+    (missing_endblock_block)
+    (missing_endblocktrans_block)
+    (missing_endblocktranslate_block)
+    (missing_endcache_block)
+    (missing_endcomment_block)
+    (missing_endfilter_block)
+    (missing_endfor_block)
+    (missing_endif_block)
+    (missing_endifchanged_block)
+    (missing_endlanguage_block)
+    (missing_endlocalize_block)
+    (missing_endlocaltime_block)
+    (missing_endpartialdef_block)
+    (missing_endspaceless_block)
+    (missing_endtimezone_block)
+    (missing_endverbatim_block)
+    (missing_endwith_block)
+    (missing_plural_block)] @error.missing_tag