xuxin930 opened a new pull request, #17868:
URL: https://github.com/apache/nuttx/pull/17868
## Summary
**Fix incorrect include directory order in CMake application configuration**
This is a bugfix for include path handling in NuttX CMake build system. The
commits address a critical issue where private (application-provided) include
directories were not taking precedence over public library includes, contrary
to expected behavior and user intent.
### Problem
Previously, the CMake code processed include directories in a loop without
the `BEFORE` keyword:
```cmake
foreach(inc ${INCLUDE_DIRECTORIES})
target_include_directories(${TARGET} PRIVATE ${inc})
endforeach()
```
This caused include directories to be appended to the end of the search
path, allowing library headers to shadow user-provided headers. The correct
behavior is: **private includes should always take precedence over public
includes**.
### Solution
The fix consolidates the loop into a single call with the `BEFORE` keyword:
```cmake
target_include_directories(${TARGET} BEFORE PRIVATE ${INCLUDE_DIRECTORIES})
```
This ensures:
1. **Correct precedence**: Private includes (first on path) > public library
includes
2. **Preserves user order**: The exact order users specified in
`INCLUDE_DIRECTORIES` is maintained
3. **CMake best practice**: Uses single target call instead of loop for
better performance and clarity
### Root Cause
The bug was introduced because the loop-based approach didn't account for
the fact that without `BEFORE`, CMake appends paths instead of prepending them.
This meant that library include paths (added via `PUBLIC` properties) would be
searched before application-local includes, breaking header precedence.
### Testing Impact
- Applications that rely on local header overrides now work correctly
- No breaking changes for properly-configured applications
- Fixes mysterious header shadowing issues where wrong versions of headers
were being included
## Impact
- **Build correctness**: Critical fix ensuring correct header precedence
rules
- **Application compatibility**: No breaking changes; fixes non-standard
behavior
- **Developer experience**: Removes confusing header shadowing bugs where
developers couldn't override library headers locally
- **CMake conformance**: Aligns with standard CMake include path semantics
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