sql/parser: YACC compilation fails on all conflicts

sql/parser/sql_union.sh

@@ -10,7 +10,7 @@ set -eu
 # to union type accessors in the Go code within rules, as the YACC
 # compiler does not type check Go code.
 function type_check() {
-    go tool yacc -o /dev/null -p sql sql.y
+    ! go tool yacc -o /dev/null -p sql sql.y | grep -F 'conflicts'
 }
 
 # This step performs the actual compilation from the sql.y syntax to
@@ -42,7 +42,7 @@ function compile() {
 
     # Compile this new "unionized" syntax file through YACC, this time writing
     # the output to sql.go.
-    go tool yacc -o sql.go -p sql sql.y
+    ! go tool yacc -o sql.go -p sql sql.y | grep -F 'conflicts'
 
     # Overwrite the migrated syntax file with the original syntax file.
     mv sql.y.tmp sql.y