⚡ Bolt: [performance improvement] Optimize D1 query generation

[bashandbone]

💡 What: Replaced intermediate vector allocations (columns, placeholders, update_clauses, where_clauses) in D1 query builders (build_upsert_stmt, build_delete_stmt) with a pre-allocated String using String::with_capacity and std::fmt::Write.

🎯 Why: SQL query generation happens frequently during D1 target synchronization. The previous implementation used multiple Vec<String> allocations and format! / join operations per query, causing unnecessary memory allocation and string copying overhead.

📊 Impact: Significantly reduces heap allocations and string formatting overhead for every D1 upsert and delete statement generated, leading to faster execution and less GC/memory churn during export operations.

🔬 Measurement: Verified by running formatting, linting, and targeted D1 target tests (cargo test -p thread-flow --test d1_target_tests --test d1_minimal_tests --test d1_cache_integration), ensuring no regressions and that the generated SQL exactly matches the previous logic.

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PR created automatically by Jules for task 12786738793941327599 started by @bashandbone

Summary by Sourcery

Optimize D1 SQL upsert and delete statement generation to reduce allocations and improve performance during target synchronization.

Enhancements:

• Replace intermediate vectors with preallocated SQL strings and direct writes in D1 upsert and delete builders to minimize memory allocations.
• Tidy up string handling and formatting in AST and rule engine modules for clearer, more consistent code.

[google-labs-jules]

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[sourcery-ai]

Reviewer's Guide

Refactors D1 upsert/delete SQL generation to build queries directly into pre-allocated Strings using fmt::Write, reducing intermediate allocations, and makes a few minor formatting/closure-style cleanups elsewhere in the codebase.

File-Level Changes

Change	Details	Files
Optimize D1 upsert SQL generation to avoid intermediate vector allocations and string joins.	Replace separate vectors for column names, placeholders, and update clauses with a single String buffer built via String::with_capacity and write!/push_str Append key column names and value column names directly into the SQL buffer while simultaneously building the params vector Generate the VALUES placeholder list by iterating over params and pushing '?' with comma separators Generate ON CONFLICT DO UPDATE SET clause in-place by iterating value_fields_schema and writing assignments into the same buffer	crates/flow/src/targets/d1.rs
Optimize D1 delete SQL generation by building the WHERE clause directly into a pre-allocated String.	Introduce a single SQL buffer initialized with DELETE FROM ... WHERE and write!/push_str for subsequent fragments Pre-allocate params vector based on key_fields_schema length Iterate key_fields_schema and append name = ? conditions directly, joining with AND using a first-element flag	crates/flow/src/targets/d1.rs
Apply minor formatting and style cleanups in AST and rule engine modules.	Reformat a from_utf8 unwrap_or_else call onto fewer lines without changing behavior Split a long assert_eq! into multiple lines for readability Expand Rule::Pattern branch in defined_vars into a multi-line iterator chain for clarity Condense a Registration::read lock/unwrap_or_else chain into a single line	crates/ast-engine/src/tree_sitter/mod.rs crates/rule-engine/src/rule/mod.rs crates/rule-engine/src/rule/referent_rule.rs

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[sourcery-ai]

Hey - I've found 1 issue, and left some high level feedback:

• In build_upsert_stmt, the number of VALUES placeholders is derived from params.len(), which implicitly assumes all params are for the insert columns only; consider tracking a dedicated placeholder count so this logic remains correct if additional parameters (e.g., for WHERE/RETURNING) are introduced in the future.
• The write! calls on a String cannot realistically fail except for formatting issues; if you don't expect dynamic formatting errors, using expect or an internal helper to avoid repetitive map_err(|e| RecocoError::internal_msg(e.to_string())) boilerplate could simplify the control flow.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- In `build_upsert_stmt`, the number of `VALUES` placeholders is derived from `params.len()`, which implicitly assumes all params are for the insert columns only; consider tracking a dedicated placeholder count so this logic remains correct if additional parameters (e.g., for WHERE/RETURNING) are introduced in the future.
- The `write!` calls on a `String` cannot realistically fail except for formatting issues; if you don't expect dynamic formatting errors, using `expect` or an internal helper to avoid repetitive `map_err(|e| RecocoError::internal_msg(e.to_string()))` boilerplate could simplify the control flow.

## Individual Comments

### Comment 1
<location path="crates/flow/src/targets/d1.rs" line_range="347-350" />
<code_context>
+            sql.push('?');
+        }
+
+        sql.push_str(") ON CONFLICT DO UPDATE SET ");
+
+        first = true;
+        for (idx, _value) in values.fields.iter().enumerate() {
+            if let Some(value_field) = self.value_fields_schema.get(idx) {
+                if !first {
</code_context>
<issue_to_address>
**issue (bug_risk):** Handle the case where there are no value fields to update in the `ON CONFLICT` clause

If `values.fields` contains no `value_field`s (e.g. only key columns or an empty payload), this will emit `... ON CONFLICT DO UPDATE SET ` with nothing after `SET`, which is invalid SQL. Since you’re already refactoring, consider guarding this case by falling back to `ON CONFLICT DO NOTHING` or omitting the `ON CONFLICT` clause when there are no updatable columns.
</issue_to_address>

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[sourcery-ai]

issue (bug_risk): Handle the case where there are no value fields to update in the ON CONFLICT clause

If values.fields contains no value_fields (e.g. only key columns or an empty payload), this will emit ... ON CONFLICT DO UPDATE SET with nothing after SET, which is invalid SQL. Since you’re already refactoring, consider guarding this case by falling back to ON CONFLICT DO NOTHING or omitting the ON CONFLICT clause when there are no updatable columns.

[Copilot]

Pull request overview

This PR optimizes D1 SQL statement generation by replacing temporary vector/string joins with direct preallocated String construction while preserving positional parameter ordering.

Changes:

• Builds D1 upsert/delete SQL using String::with_capacity and write!.
• Preallocates parameter vectors based on schema/value sizes.
• Applies rustfmt-only formatting changes in unrelated rule/tree-sitter files.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
crates/flow/src/targets/d1.rs	Optimizes D1 upsert and delete SQL builders.
crates/rule-engine/src/rule/referent_rule.rs	Formatting-only change.
crates/rule-engine/src/rule/mod.rs	Formatting-only change.
crates/ast-engine/src/tree_sitter/mod.rs	Formatting-only changes in string handling and a test assertion.

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