Fix build-SITL-Mac VLA-folding-constant error in log.c

[sensei-hacker]

Summary

Fixes the build-SITL-Mac CI failure on maintenance-10.x: AppleClang errors on src/main/common/log.c:210 under -Werror -Wgnu-folding-constant.

Root Cause

_logBufferHex() sizes a stack buffer with:

const size_t charsPerByte = 5;
const size_t maxBytes = 8;
char buf[LOG_PREFIX_FORMATTED_SIZE + charsPerByte * maxBytes + 1];

In C (unlike C++), a const-qualified object is not an integer constant expression. So this array size is technically a variable-length array. Compilers have long tolerated this via a GNU extension that folds it back to a fixed size when the value happens to be known — but a newer AppleClang on the macOS CI runner now warns (and -Werror promotes to error) when code relies on that extension.

Fix

Replace the two const size_t locals with a local enum:

enum {
    charsPerByte = 5,
    maxBytes = 8,
};

Enum constants are genuine integer constant expressions in C (C11 6.6p6), so the buffer size expression is now a real compile-time constant on every compiler — not just one that happens to fold it. This removes the VLA classification at the root rather than suppressing the warning.

No behavior change: buffer size is 13 + 5*8 + 1 = 54 bytes both before and after.

Testing

• Full clean SITL build (Linux/GCC) succeeds with no warnings or errors in log.c.
• Verified via minimal reproduction that const size_t locals vs. enum constants differ in constant-expression classification per the C standard (C11 6.6p6 explicitly lists enumeration constants as valid ICE operands, and excludes const-qualified objects).
• build-SITL-Mac CI leg on this PR will provide the authoritative confirmation against the actual AppleClang toolchain that originally reported the error.
• No log output formatting change — only the kind of constant used to compute a buffer size changed, not its value.

Code Review

Reviewed with inav-code-review agent — no critical or important issues found. Approved.

Fixes the build-SITL-Mac failure reported against maintenance-10.x (see PR #11678 CI for original occurrence).

[qodo-code-review]

PR Summary by Qodo

Fix AppleClang VLA folding-constant build error in _logBufferHex()

🐞 Bug fix 🕐 10-20 Minutes

AI Description

• Fix macOS SITL build failure caused by AppleClang treating a non-constant array size as a VLA
• Replace const size_t locals with enum constants so the stack buffer size is a true ICE in C
• Preserve behavior and buffer size while eliminating reliance on GNU constant-folding extensions

Diagram

graph TD
  A["build-SITL-Mac CI"] --> B["AppleClang (-Werror)"] --> C["src/main/common/log.c"] --> D["_logBufferHex()"] --> E["ICE-sized stack buffer"] --> F["Build succeeds"]

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High-Level Assessment

The following are alternative approaches to this PR:

1. Use preprocessor macros (#define) for constants

• ➕ Guaranteed compile-time constants in C
• ➕ Clear intent for fixed sizes
• ➖ Pollutes macro namespace
• ➖ Harder to scope to a single function without naming ceremony

2. Use a file-scope enum/const for shared reuse

• ➕ Avoids repeating constants if used elsewhere
• ➕ Still provides true compile-time constants (enum)
• ➖ Unnecessary wider scope for a purely local formatting detail
• ➖ Slightly increases global surface area

3. Suppress/relax the warning on macOS build

• ➕ Minimal code churn
• ➖ Masks a real standards issue (VLA classification)
• ➖ Build flags become toolchain-specific and harder to maintain

Recommendation: The PR’s local enum approach is the best trade-off: it keeps the constants scoped to the function, produces a true integer constant expression in C on all compilers, and avoids weakening warnings or introducing global macros.

Files changed (1) +6 / -2

Bug fix (1) +6 / -2

log.cMake _logBufferHex() buffer size a true C constant expression +6/-2

Make _logBufferHex() buffer size a true C constant expression

• Replaces two 'const size_t' locals used in an array bound with local 'enum' constants so the bound is a true integer constant expression in C. This avoids AppleClang treating the array as a VLA under '-Wgnu-folding-constant' + '-Werror', while keeping the buffer size and behavior unchanged.

src/main/common/log.c

[qodo-code-review]

Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0)

Great, no issues found!

Qodo reviewed your code and found no material issues that require review

[github-actions]

Test firmware build ready — commit b13c96a

Download firmware for PR #11679

238 targets built. Find your board's .hex file by name on that page (e.g. MATEKF405SE.hex). Files are individually downloadable — no GitHub login required.

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