misc(native): Clean up SystemConnector: fix fragile statics, macro hygiene, const-correctness, and switch safety

[amitkdutta]

Summary:
Several code quality issues in SystemConnector accumulated over time:

B1: Fix std::move from static local vectors in taskSchema()
kTaskColumnNames and kTaskColumnTypes were mutable static vectors that got std::moved into the ROW() constructor. After the first call, these vectors would be in a moved-from (empty) state. The code worked by accident because kTaskSchema is also static and initialized once, but it was fragile and confusing. Replaced with a single static const RowTypePtr constructed directly.

B2: Fix macro copy-by-value and add #undef
SET_TASK_COLUMN and SET_TASK_FMT_COLUMN macros copied task (shared_ptr) and taskInfo (TaskInfo struct) by value on every loop iteration. Changed to const auto& references with [[maybe_unused]] since each macro expansion may use only one of the two variables. Added #undef after use.

B4: Add const to SystemSplit accessors
schemaName() and tableName() returned const std::string& but were not const-qualified, preventing use on const SystemSplit&.

B5: Add default case to getTaskResults() switch
The switch over TaskColumnEnum had no default clause. Adding a new column enum without updating the switch would silently skip population. Added default: VELOX_UNREACHABLE().

== NO RELEASE NOTE ==

Summary by Sourcery

Improve SystemConnector code safety and const-correctness for task metadata handling.

Bug Fixes:

• Replace fragile static mutable task schema vectors with a single static const RowType definition.
• Ensure getTaskResults() handles future TaskColumnEnum additions by adding a default switch case that fails fast.

Enhancements:

• Avoid unnecessary copying in task column helper macros by using referenced task/taskInfo variables and cleaning up macro scope with undef directives.
• Make SystemSplit schemaName() and tableName() accessors const-qualified to support use on const instances.

[sourcery-ai]

Reviewer's Guide

Refactors SystemConnector task schema construction and task population macros to be safer and more efficient, improves const-correctness of SystemSplit accessors, and hardens the task results switch with an explicit unreachable default.

Class diagram for updated SystemConnector components

classDiagram
  class SystemTableHandle {
    +RowTypePtr taskSchema() const
  }

  class SystemDataSource {
    +RowVectorPtr getTaskResults()
    +std::optional~RowVectorPtr~ next(uint64_t size, ContinueFuture& future)
  }

  class SystemSplit {
    +SystemSplit(const std::string& schemaName, const std::string& tableName)
    +const std::string& schemaName() const
    +const std::string& tableName() const
    -std::string schemaName_
    -std::string tableName_
  }

  SystemDataSource ..> SystemSplit : uses_splits
  SystemTableHandle ..> SystemDataSource : defines_schema_for

Loading

File-Level Changes

Change	Details	Files
Make taskSchema() use a single static const RowTypePtr instead of mutable static vectors that are moved-from.	Inline the task column names directly into the ROW() call as an initializer list. Inline the task column types directly into the ROW() call using velox::VARCHAR/BIGINT/TIMESTAMP factories. Remove mutable static std::vector instances and std::move usage, leaving a single static const RowTypePtr kTaskSchema.	presto-native-execution/presto_cpp/main/connectors/SystemConnector.cpp
Improve macro hygiene and efficiency for task column population.	Change SET_TASK_COLUMN to bind task and taskInfo as [[maybe_unused]] const auto& instead of copying by value. Change SET_TASK_FMT_COLUMN similarly and keep a reusable std::string temp for formatting. Add VELOX_UNREACHABLE() as the default case in the TaskColumnEnum switch inside getTaskResults(). Add #undef for SET_TASK_COLUMN and SET_TASK_FMT_COLUMN after their last use to avoid macro leakage.	presto-native-execution/presto_cpp/main/connectors/SystemConnector.cpp
Make SystemSplit accessors const-correct.	Mark schemaName() as a const method returning const std::string&. Mark tableName() as a const method returning const std::string&.	presto-native-execution/presto_cpp/main/connectors/SystemSplit.h

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