bcquality/microsoft/knowledge/style/variable-name-must-not-shadow.md
Jesper Schulz-Wedde a9f3c50863 Regenerate microsoft/knowledge from upstream BCApps instructions
The previous LLM-generated knowledge files contained factual
hallucinations. The most visible was the claim that `FindFirst` /
`FindLast` "forces a full-table scan" on an unfiltered record - it does
not; those APIs return a single row via the current key.

Other inaccuracies the audit found and fixed:

* `FindSet(true)` was described as "taking a LockTable". The correct
  upstream phrasing is that `FindSet(true)` sets
  `ReadIsolation::UpdLock` on the read. UpdLock and LockTable are
  related but distinct mechanisms.
* The list of production-scale tables had been invented beyond the
  upstream source (e.g. "Detailed Cust. Ledg. Entry") without a
  citation. The regenerated list matches the ten tables upstream lists
  with their P95 row counts.
* `SetLoadFields` guidance had been augmented with an extra mechanism
  claim ("the database resolves the filter using the index without
  hydrating the value") not present in upstream.

Approach: full regeneration of `microsoft/knowledge/` from the six
upstream BCApps Code Review instruction files, with Microsoft Learn /
the AL language reference as a secondary source. Every claim in every
regenerated file is anchored to a verbatim upstream quote (or a Learn
URL); the audit trail lives in artifacts/trace-<domain>.json on the
session workspace.

The PR #11 transaction/error-handling cluster is preserved verbatim:

* performance/understand-implicit-transaction-boundary.md
* performance/codeunit-run-as-atomic-sub-operation.{md,good.al,bad.al}
* performance/codeunit-run-requires-prior-commit-inside-transaction.{md,good.al,bad.al}
* performance/use-tryfunction-for-error-catching-not-rollback.{md,good.al,bad.al}
* performance/avoid-commit-inside-loops.{md,good.al,bad.al}
* security/commitbehavior-attribute-scopes-explicit-commits.{md,good.al,bad.al}
* testing/transactionmodel-attribute-governs-test-transactions.{md,good.al,bad.al}

These articles already cite Microsoft Learn and were carefully
cross-referenced; the regeneration skips their topics rather than
duplicating them.

File counts after regeneration:

  performance   35 .md  (5 preserved + 30 new)
  privacy       17 .md
  security      18 .md  (1 preserved + 17 new)
  style         33 .md
  testing        1 .md  (preserved)
  ui            19 .md
  upgrade       18 .md

Total 141 atomic knowledge files, each strictly one rule. All pass
.github/scripts/validate_frontmatter.py with 0 errors and 0 warnings.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
2026-05-21 09:53:09 +02:00

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1.7 KiB
Markdown

---
bc-version: [all]
domain: style
keywords: [variable-name, shadow, conflict, aa0198, aa0202, aa0204, codecop]
technologies: [al]
countries: [w1]
application-area: [all]
---
# Local variable names must not shadow globals, fields, methods, or actions (CodeCop AA0198/AA0202/AA0204)
## Description
Three CodeCop rules — AA0198, AA0202, AA0204 — together forbid a local variable from sharing a name with a global variable on the same object, with a field on the same table or page source, with a procedure on the same object, or with an action on the same page. The compiler resolves the conflict by binding the closer scope, so a local `Customer: Text` will silently override a global `Customer: Record Customer` for the duration of a procedure — every call site reading `Customer.Name` from inside that procedure refers to the text, and the breakage is invisible to a reader who has both declarations on screen.
## Best Practice
Differentiate every local declaration from globals, fields, procedures, and actions on the same object. `Customer` global plus `CustomerName` local; method `GetAmount` plus local `SalesAmount`. The standard pattern is to attach a noun suffix to the local (`CustomerName`, `CustomerRec`, `CustomerNo`) rather than to the global.
See sample: `variable-name-must-not-shadow.good.al`.
## Anti Pattern
A procedure that declares a local `Customer: Text` inside a codeunit that already has a global `Customer: Record Customer`. The local wins and the global becomes unreachable inside the procedure. AA0198/AA0202/AA0204 flag this category of conflict whether the colliding entity is a global, a field, a method, or an action.
See sample: `variable-name-must-not-shadow.bad.al`.