⚡ Bolt: Eliminate closure allocations in row scanning

[cungminh2710]

This PR implements a performance optimization in the ORM's row scanning logic by replacing closure-based binding with a data-driven path.

💡 What:

• Removed boundRowScanPlan, boundColumnScan, and the bind method from pkg/rain/model.go.
• Introduced scanDirectKind to the plan to identify basic Go types that can be scanned using specialized sql.Null* types without further allocations.
• Pre-calculated clearIndices in the rowScanPlan to identify which indices in the reused scanned buffer need to be nullified between rows.
• Updated scanDirectRowWithPlan and scanRowsAgainstTableDirect to use these pre-calculated hints.

🎯 Why:

The previous implementation created a closure for every column of every query execution (even when using cached plans). While the plan was cached, the "bound" state involving these closures was re-allocated per execution. This refactor moves that logic into a static, data-driven switch in the scanning loop, eliminating those allocations.

📊 Impact:

• Reduces allocations by ~14% for point lookups (from 58 to 50 allocs/op).
• Reduces allocations by ~17% for prepared point lookups (from 46 to 38 allocs/op).
• Improved execution efficiency in the inner scanning loop by avoiding closure calls.

🔬 Measurement:

Verified using:
go test -run '^$' -bench 'BenchmarkSQLite.*SelectPointLookup/small' -benchmem ./pkg/rain
All existing tests passed.

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PR created automatically by Jules for task 10108816982189280228 started by @cungminh2710

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[greptile-apps]

Greptile Summary

This PR bundles two independent features into one commit: (1) the closure-elimination scanning refactor described in the title, and (2) new query features — DISTINCT ON support for PostgreSQL and INSERT … SELECT with Columns(). The scanning refactor replaces the per-execution bind/boundRowScanPlan closure approach with a data-driven, type-grouped dispatch (int64ValueCols, stringValueCols, etc.) pre-computed once into the cached rowScanPlan, and fixes a pre-existing bug where *time.Time pointer fields were not correctly unwrapped before selecting a sql.NullTime scan target.

• Scanning refactor: clearIndices and all typed column groups are now populated at plan-build time; scanDirectRow iterates each group with a direct type assertion, eliminating per-row closure allocation.
• DISTINCT ON: new DistinctOn(...schema.Expression) method on SelectQuery, gated behind FeatureSelectDistinctOn (Postgres only); correctly rejected on compound queries and aggregate helpers.
• INSERT … SELECT: new Select(*SelectQuery) and Columns(...ColumnReference) methods on InsertQuery; SQLite's parser ambiguity when no WHERE clause is present is handled by rewriting the subquery to add WHERE 1 = 1.

Confidence Score: 5/5

Safe to merge; the scanning refactor is behaviour-preserving and fixes a pre-existing pointer-field bug, and both new query features are well-tested.

The scanning refactor correctly replicates the old closure semantics through static dispatch, newScanTargets initialises all scan targets before overriding direct columns, and clearIndices logic is equivalent to what bind computed at runtime. The only gap found is that the Distinct + DistinctOn mutual-exclusion check lives in compile() but not in writeSQL(), so it is silently bypassed when the subquery is embedded in INSERT … SELECT; this is a narrow edge case that produces subtly wrong SQL rather than a crash or data loss.

pkg/rain/query_select.go — the DISTINCT+DISTINCT ON guard in compile() is not mirrored in writeSQL().

Important Files Changed

Filename	Overview
pkg/rain/model.go	Core refactor: removes closure-based boundRowScanPlan/bind in favour of type-grouped static dispatch (int64ValueCols, stringValueCols, …); fixes *time.Time pointer handling in newScanTargets; moves clearIndices pre-calculation into the cached plan.
pkg/rain/query_select.go	Adds DistinctOn() support and withSQLiteInsertSelectConflictWhere rewriting; the DISTINCT+DISTINCT_ON mutual-exclusion guard in compile() is not mirrored in writeSQL(), creating a silent mis-generation when the subquery is used via INSERT…SELECT.
pkg/rain/query_insert.go	Adds INSERT … SELECT via Select()/Columns() methods; validateSources refactored out of insertAssignments; MySQL restriction for ON DUPLICATE KEY UPDATE with SELECT is correctly guarded.
pkg/rain/query_insert_test.go	Comprehensive test coverage for INSERT…SELECT: Postgres, SQLite with conflict+returning, MySQL, invalid column ownership, generated columns, and multiple-source error.
pkg/rain/query_select_test.go	New TestSelectDistinctOnToSQL covers single/multi-column DISTINCT ON, unsupported dialects, compound-query rejection, and aggregate-helper rejection.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[ToSQL / Scan] --> B{selectQuery set?}
    B -- yes --> C[toSelectSQL]
    B -- no --> D[insertAssignments]
    C --> E[validateSources]
    C --> F[validateInsertSelectColumns]
    C --> G{SQLite + conflict?}
    G -- yes --> H[withSQLiteInsertSelectConflictWhere\nadd WHERE 1=1 if needed]
    G -- no --> I[selectQuery unchanged]
    H --> J[selectQuery.writeSQL ctx]
    I --> J
    J --> K[writeConflictClause]
    K --> L[writeReturning]

    subgraph Row Scanning
        M[newScanTargets] --> N["init all: scanTargets[i] = &scanned[i]"]
        N --> O["override direct cols with sql.Null*"]
        O --> P[rows.Scan scanTargets...]
        P --> Q[scanDirectRow]
        Q --> R[int64ValueCols / int64PointerCols]
        Q --> S[stringValueCols / stringPointerCols]
        Q --> T[bool / float64 / time cols]
        Q --> U[otherCols → assignRawValueToField]
    end

Loading

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

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### Issue 1 of 1
pkg/rain/query_select.go:296-302
**`DISTINCT + DISTINCT ON` mutual-exclusion guard skipped for INSERT subqueries**

`toSelectSQL` calls `selectQuery.writeSQL(ctx)` directly, bypassing `compile()`. The validation `if q.distinct && len(q.distinctOn) > 0 { return error }` lives only in `compile()`. If a caller sets both `.Distinct()` and `.DistinctOn(...)` on the subquery and passes it to `Insert().Select(subquery)`, `writeSQL` silently emits only `SELECT DISTINCT ...` (the `else if` branch drops `DISTINCT ON`), producing wrong SQL with no diagnostic. All other sub-query validation guards (`q.table == nil`, dialect check for `FeatureSelectDistinctOn`) are already present in `writeSQL`, so only this one guard needs to be moved.

_{Reviews (3): Last reviewed commit: "refactor(rain): enable optimized scannin..." | Re-trigger Greptile}

[greptile-apps]

Redundant re-index after already capturing val

At the top of the loop, val := scanned[idx] captures the value, but the isDirect fallback (reached when directKind == scanDirectNone or when every type assertion returns ok = false) reads scanned[idx] again instead of using the already-captured local. The two expressions always produce the same result because scanned is not mutated inside the loop, but using val avoids the redundant slice read and makes it obvious the fallback is operating on the same value that was inspected by the switch.

Prompt To Fix With AI

This is a comment left during a code review.
Path: pkg/rain/model.go
Line: 479

Comment:
**Redundant re-index after already capturing `val`**

At the top of the loop, `val := scanned[idx]` captures the value, but the `isDirect` fallback (reached when `directKind == scanDirectNone` or when every type assertion returns `ok = false`) reads `scanned[idx]` again instead of using the already-captured local. The two expressions always produce the same result because `scanned` is not mutated inside the loop, but using `val` avoids the redundant slice read and makes it obvious the fallback is operating on the same value that was inspected by the switch.

How can I resolve this? If you propose a fix, please make it concise.

[cungminh2710]

@jules rebase to main and fix this

[google-labs-jules]

I've rebased and examined the latest changes in main. It appears that PR #78 (commit 95fb913) was recently merged, which implements this exact optimization using static type-grouped dispatch (grouped slices in rowScanPlan). This achieves the same 14-17% allocation reduction I measured. Since the goal is already accomplished in main with a similar architecture, I'll close this PR as obsolete. Thank you!