cpp-static-analysis

name	cpp-static-analysis
description	Use when asked to fix static analysis violations in C/C++ code — from clang-tidy, cppcheck, Coverity, MISRA C:2012, or AUTOSAR C++14 reports. Provides a safe per-rule fix workflow that prevents cascading new violations. Covers AUTOSAR C++14, MISRA C:2012, CERT C++, and clang-tidy findings. Does NOT cover tool setup or CI/CD configuration.
argument-hint	<rule-id|file|report>

C/C++ Static Issue Fix Workflow

This skill guides safe, rule-by-rule remediation of static analysis findings in automotive C/C++ codebases. It is designed to prevent the common failure mode where fixing one rule introduces a violation of another.

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When to Use This Skill

• A task says "fix static issues", "clean up warnings", "fix MISRA violations", etc.
• IDE / problems panel shows clang-tidy or cppcheck warnings.
• User pastes a Coverity, PC-lint, or static analysis report.
• A commit diff contains // NOLINT or // cppcheck-suppress that needs review.
• Pre-commit: final scan before pushing code for review.

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Source of Issues

Three intake paths — all lead to the same fix workflow:

Path	How to collect	Rule ID available?
IDE / problems tool	Use problems tool to list active diagnostics	Yes — clang-tidy check name or rule ID
Self-review	Use changes tool on staged diff; codebase search for patterns	Sometimes — derive from pattern
Report text	User pastes Coverity / PC-lint output	Yes — Coverity CID or rule ID

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Fix Workflow — Follow in Order

Step 1: Collect & Group Issues

Gather all issues from the available source. Group them by Rule ID:

AUTOSAR M5-0-2   → 4 occurrences in AudioManager.cpp
AUTOSAR A7-1-1   → 2 occurrences in SensorDriver.cpp
MISRA C 14.4     → 1 occurrence in can_driver.c
clang-tidy modernize-use-nullptr → 6 occurrences across 3 files

Never mix rule IDs in a single fix pass.

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Step 2: Prioritize

Fix in this order:

1. Mandatory / Required rules (MISRA Required, AUTOSAR Required) — safety-critical.
2. Advisory rules — quality improving.
3. clang-tidy modernization / style findings — lowest risk.

If the report comes from Coverity: fix High severity defects first.

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Step 3: Load the Rule Guide

For each Rule ID, load its guide from the cpp-static-analysis/references/ subfolder:

Rule ID pattern	Reference path
AUTOSAR A* or AUTOSAR M*	cpp-static-analysis/references/autosar-cpp14/<RULE-ID>.md
MISRA C *	cpp-static-analysis/references/misra-cpp/<RULE-ID>.md
CERT C++ *	cpp-static-analysis/references/cert-cpp/<RULE-ID>.md
clang-tidy check	cpp-static-analysis/references/static/<check-name>.md

If no guide file exists yet for this rule:

1. Inform the user: "No per-rule guide for <ID> yet. Add cpp-static-analysis/references/<category>/<ID>.md when this rule recurs."
2. Fall back to lang-cpp-code-writing / lang-c-code-writing for general idiom guidance, but proceed conservatively — prefer the minimal transformation.
3. Always verify the fix does not trigger related rules (see Step 5).

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Step 4: Apply the Compliant Transformation

Use only the transformation pattern described in the rule guide.

Rules for applying fixes:

• Fix one rule at a time — complete all occurrences of Rule X before moving to Rule Y.
• Change only the lines necessary — do not reformat surrounding code.
• Do not change related code "while you're there" — separate commits.
• If a fix requires changes in more than one file, apply them in the same commit but document all affected files in the commit message.

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Step 5: Post-Fix Verification

After fixing all occurrences of a rule, verify with the Post-Fix Checklist from the rule guide. If no guide exists, manually check:

1. Re-read the modified lines — does the fix match the "Compliant" example?
2. Check the Related Rules list in the guide. For each related rule, scan the modified lines for a new violation.
3. Compile mentally: are there new implicit conversions, narrowing, or type changes introduced?
4. If problems tool is available: re-run and confirm the finding is gone and no new findings appeared in the same file.

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Step 6: Suppression (Last Resort)

If a fix is technically impossible (e.g., hardware register access requires reinterpret_cast, or a third-party API forces a narrowing conversion):

// NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
// Justification: Direct MMIO register access mandated by BSP spec §4.2.
// Deviation permit: PROJ-DEV-042 — approved by safety architect.
volatile uint32_t* reg = reinterpret_cast<volatile uint32_t*>(kBaseAddr);

Rules for suppression:

• Every // NOLINT or // cppcheck-suppress must have a justification comment.
• Bare // NOLINT with no reason is not acceptable — treat it as a new violation.
• Suppression of MISRA Mandatory rules requires a formal deviation permit reference.

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Step 7: Commit

One commit per Rule ID (or one commit per logical group of the same rule across files):

static(<scope>): fix AUTOSAR M5-0-2 narrowing conversion in AudioManager

Replaced implicit narrowing int→uint8_t with explicit static_cast.
Post-fix: verified no new A4-7-1 (overflow) violations introduced.

Commit type: static — see project commit convention.

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Quick Reference — Common Patterns Without a Guide

Use these only when no cpp-static-analysis/references/ guide exists for the rule.

Narrowing conversion (AUTOSAR M5-0-2 / MISRA 10.3)

// ❌ Implicit narrowing
uint8_t val = some_int_expr;

// ✅ Explicit cast — add bounds assertion if value range is not proven
assert(some_int_expr >= 0 && some_int_expr <= 255); // or static_assert
uint8_t val = static_cast<uint8_t>(some_int_expr);

Boolean context (MISRA C 14.4)

// ❌ Non-boolean controlling expression
if (ptr) { ... }
if (count) { ... }

// ✅ Explicit comparison
if (ptr != nullptr) { ... }
if (count != 0U) { ... }

constexpr (AUTOSAR A7-1-1)

// ❌ const value known at compile time
const uint32_t kMaxRetries = 5U;

// ✅
constexpr uint32_t kMaxRetries = 5U;

Explicit new/delete (AUTOSAR A18-5-2)

// ❌
Sensor* s = new TemperatureSensor(id);
delete s;

// ✅
auto s = std::make_unique<TemperatureSensor>(id);

nullptr over NULL / 0 (clang-tidy modernize-use-nullptr)

// ❌
if (ptr == NULL) { ... }
callback_fn = 0;

// ✅
if (ptr == nullptr) { ... }
callback_fn = nullptr;

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Cross-Rule Contamination Map

The most common fix-triggers-new-violation patterns. Always check these after applying the primary rule fix:

Fix applied	Common new violation to check
Added static_cast<T> (M5-0-2)	A4-7-1 — arithmetic result within type range?
Added static_cast<T>	MISRA 10.5 — appropriate essential type cast?
Changed const to constexpr (A7-1-1)	Does expression remain valid in constexpr context?
Replaced new with make_unique (A18-5-2)	A8-4-7 — ownership transfer via parameter correct?
Added != nullptr check (MISRA 14.4)	Redundant null check if pointer already validated upstream?
Replaced NULL with nullptr	Function overload resolution changed?
Removed reinterpret_cast	Does the replacement static_cast preserve MMIO semantics?

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Prerequisites

• GCC 9+ or Clang 12+ toolchain installed.
• CMake 3.16+ on PATH.
• For cross-compilation: ARM/AArch64 sysroot or Android NDK r25+.
• ninja build tool recommended for faster builds.

Step-by-Step Workflows

The step-by-step fix workflow is defined in the Fix Workflow section below. Summary: collect violation report → fix one rule at a time → rebuild to confirm no regression → commit per rule.

Troubleshooting

• Fix introduced a new violation — re-run the tool after each rule batch; revert and refine if new violations appear.
• clang-tidy takes too long — run on changed files only: clang-tidy $(git diff --name-only HEAD | grep -E '\.(cpp|hpp|h)$').
• False positive from a third-party header — add the header path to HeaderFilterRegex in .clang-tidy to exclude it from reporting.
• Suppression comment not working — for clang-tidy use // NOLINT(<check-name>) at the end of the violating line; for cppcheck use // cppcheck-suppress <id>.

References Folder Layout

cpp-static-analysis/references/
├── autosar-cpp14/     ← one .md per AUTOSAR rule (e.g., M5-0-2.md, A7-1-1.md)
├── misra-cpp/         ← one .md per MISRA rule (e.g., 14-4.md, 10-3.md)
├── cert-cpp/          ← one .md per CERT rule
└── static/            ← one .md per clang-tidy check or cppcheck category

Add a new rule guide whenever a rule is encountered for the first time. Each rule guide file follows this template:

# Rule: <ID> — <short title>

## Rule Statement
Exact wording from the standard (no paraphrasing).

## Trigger Patterns
Code patterns that cause a violation — with examples.

## Compliant Transformations
Exact transformation to apply — before/after code samples.

## What NOT To Do
Wrong "fixes" that still violate this rule or introduce a new one.

## Post-Fix Verification Checklist
- [ ] Check these related rules after applying the fix.

## Suppression (if unavoidable)
Correct suppression annotation with required justification format.