fix(verifier): request larger stack size for new solver (#5883)

In the future we can look at doing a smarter job lowering to datalog
(e.g. not adding every goal into the same giant Horn clause, which was
causing souffle to bump up against the stack). For now, just asking for
a larger stack allows all the Go tests to pass; tested this by running
them with the flag fixed to true.

kythe/cxx/verifier/verifier_main.cc

@@ -15,6 +15,7 @@
  */
 
 #include <stdio.h>
+#include <sys/resource.h>
 #include <unistd.h>
 
 #include <string>
@@ -69,6 +70,11 @@ ABSL_FLAG(bool, use_fast_solver, false,
 ABSL_FLAG(bool, print_timing_information, false,
           "Print timing information for profiling.");
 
+namespace {
+// The fast solver needs extra stack space for modest programs.
+constexpr rlim_t kSolverStack = 64L * 1024L * 1024L;
+}  // namespace
+
 int main(int argc, char** argv) {
   GOOGLE_PROTOBUF_VERIFY_VERSION;
   kythe::InitializeProgram(argv[0]);
@@ -139,6 +145,23 @@ invocation and rule syntax.
 
   v.UseFastSolver(absl::GetFlag(FLAGS_use_fast_solver));
 
+  if (absl::GetFlag(FLAGS_use_fast_solver)) {
+    struct rlimit rl;
+    int r = getrlimit(RLIMIT_STACK, &rl);
+    if (r != 0) {
+      perror("failed getting solver stack size");
+      return 1;
+    }
+    if (rl.rlim_cur < kSolverStack) {
+      rl.rlim_cur = kSolverStack;
+      r = setrlimit(RLIMIT_STACK, &rl);
+      if (r != 0) {
+        perror("failed increasing solver stack size");
+        return 1;
+      }
+    }
+  }
+
   std::string dbname = "database";
   size_t facts = 0;
   auto start_read_time = absl::Now();