trace_processor: significantly improve error handling in span join

Until now, we were trying to make do with mediocre error messages
because we had no way of propogating errors properly from span join
up to the table code.

Refactor Table::Init to allow this to happen correctly with the error
reported directly to SQLite.

Change-Id: Ie84657e74b74cc49f5fecada24aea7ef810223dc

src/trace_processor/table.h

diff --git a/src/trace_processor/table.h b/src/trace_processor/table.h
index 58c9d18..0405eb9 100644
--- a/src/trace_processor/table.h
+++ b/src/trace_processor/table.h
@@ -25,6 +25,7 @@
 #include <vector>
 
 #include "perfetto/base/optional.h"
+#include "perfetto/trace_processor/basic_types.h"
 #include "src/trace_processor/query_constraints.h"
 
 namespace perfetto {
@@ -175,19 +176,19 @@
     memset(module, 0, sizeof(*module));
 
     auto create_fn = [](sqlite3* xdb, void* arg, int argc,
-                        const char* const* argv, sqlite3_vtab** tab, char**) {
+                        const char* const* argv, sqlite3_vtab** tab,
+                        char** pzErr) {
       const TableDescriptor* xdesc = static_cast<const TableDescriptor*>(arg);
       auto table = xdesc->factory(xdb, xdesc->storage);
       table->name_ = xdesc->name;
 
-      auto opt_schema = table->Init(argc, argv);
-      if (!opt_schema.has_value()) {
-        PERFETTO_ELOG("Failed to create schema (table %s)",
-                      xdesc->name.c_str());
+      Schema schema;
+      util::Status status = table->Init(argc, argv, &schema);
+      if (!status.ok()) {
+        *pzErr = sqlite3_mprintf("%s", status.c_message());
         return SQLITE_ERROR;
       }
 
-      const auto& schema = opt_schema.value();
       auto create_stmt = schema.ToCreateTableStmt();
       PERFETTO_DLOG("Create table statement: %s", create_stmt.c_str());
 
@@ -274,7 +275,7 @@
   }
 
   // Methods to be implemented by derived table classes.
-  virtual base::Optional<Schema> Init(int argc, const char* const* argv) = 0;
+  virtual util::Status Init(int argc, const char* const* argv, Schema*) = 0;
   virtual std::unique_ptr<Cursor> CreateCursor() = 0;
   virtual int BestIndex(const QueryConstraints& qc, BestIndexInfo* info) = 0;