Checks reference

Every check plc-st-review ships with, what it catches, why it exists, how to configure it, an ST trigger, what the bot posts, and a suggested fix. See check-limitations.md for what each check deliberately doesn't catch.

Live demo: every check in this document fires at least once on PR #1, where you can see the exact inline comments the bot posts.

Common settings (apply to every check)

Two knobs work on every check, set in .plc-st-review.yml:

severity_overrides:
  CATEGORY_NAME: error      # raise / lower the severity for this category
disabled_checks:
  - CATEGORY_NAME           # turn the check off entirely

Each per-check page below only lists additional knobs (check-specific config, prefix lists, etc.).

Diff-based checks

These compare the before and after trees of a PR. Every finding implies a change happened in this PR.

• SIGNATURE_CHANGED
• CALL_SITE_OUTDATED
• TYPE_MISMATCH
• ENUM_VALUE_REMOVED
• ENUM_VALUE_ADDED
• TIMER_VALUE_CHANGED
• CONSTANT_VALUE_CHANGED
• COMMENT_ONLY
• ARRAY_BOUNDS_CHANGED
• STATE_UNHANDLED
• UNREACHABLE_CODE
• LOOP_BOUNDS_CHANGED
• POU_DELETED
• POU_RENAMED
• METHOD_ADDED_TO_INTERFACE
• INHERITANCE_CHANGED
• PRAGMA_CHANGED
• UNUSED_VAR_INTRODUCED
• COUNTER_VALUE_CHANGED

Static integrity checks

These run on the after tree alone and surface bugs that compile but mis-behave. Each one filters out findings already present in the before tree so the check only flags new problems introduced in the PR.

• ENUM_VALUE_UNUSED
• ENUM_MEMBER_UNKNOWN
• ARRAY_INDEX_OUT_OF_BOUNDS
• DIVISION_BY_ZERO
• INFINITE_LOOP
• LOOP_BOUNDS_REVERSED

FB-instance checks

These target standard IEC 61131-3 function-block patterns (TON, CTU, R_TRIG, SR/RS, etc.), wiring mistakes that won't trip a normal compiler but produce wrong runtime behavior.

• COUNTER_PV_ZERO
• TIMER_PT_ZERO
• TIMER_NOT_DRIVEN
• EDGE_TRIG_REUSED
• FB_INSTANCE_DOUBLE_CALL
• FB_INSTANCE_NEVER_CALLED
• BISTABLE_DOMINANCE_MISMATCH

Code-quality and style checks

These are stylistic / hygiene checks. Most ship at info severity and stay off your blocking gate by default; raise them in .plc-st-review.yml once your team agrees on a convention.

• EMPTY_STATEMENT
• UNUSED_RETURN_VALUE
• ARRAY_SINGLE_ELEMENT
• VARIABLE_SHADOWING
• UNQUALIFIED_ENUM_CONSTANT
• IDENTIFIER_CASE_MISMATCH
• UNUSED_INPUT_VAR
• INPUT_VAR_WRITTEN
• BOOL_COMPARISON
• REAL_EQUALITY
• MULTIPLE_EXIT_POINTS
• ASSIGNMENT_IN_CONDITION
• COMMENTED_OUT_CODE
• RECURSIVE_CALL
• FORBIDDEN_SYMBOL
• ADDRESS_OF_CONSTANT
• UNUSED_OUTPUT_VAR
• OUTPUT_VAR_READ_INTERNALLY
• NESTED_COMMENTS
• NAMING_CONVENTION

Using a check in your PR

plc-st-review runs automatically once you've set up the GitLab or GitHub integration (see gitlab-setup.md / github-setup.md). Every check above lands as either an inline comment on the relevant .st line or as part of the summary issue / discussion comment when the affected line falls outside the PR's diff hunks.

To suppress a check for a single repo, add it to disabled_checks in .plc-st-review.yml. To raise or lower its severity, use severity_overrides. See tuning-severities.md for the tuning ramp.

To compose policy across many repos, naming conventions, severity profiles, forbidden symbols, use extends: to pull from shared preset files. See preset-packs.md.