Fix SIGBUS when saving PNG on Apple Silicon

[krystophny]

User description

Summary

• add zlib_compress_into subroutine to avoid returning large allocatables from functions
• keep existing zlib_compress function as wrapper for backwards compatibility
• update raster/pdf backends to call the new helper and add optional debug logging

Testing

• fpm test

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PR Type

Bug fix, Enhancement

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Description

• Add zlib_compress_into subroutine to avoid returning large allocatables

• Keep existing zlib_compress function as backwards-compatible wrapper

• Update PNG and PDF backends to use new helper

• Add optional debug logging with environment variable control

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Diagram Walkthrough

flowchart LR
  A["zlib_compress function"] --> B["zlib_compress_into subroutine"]
  B --> C["PNG backend"]
  B --> D["PDF backend"]
  B --> E["Debug logging"]
  A --> F["Backwards compatibility wrapper"]

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File Walkthrough

	Relevant files
Enhancement	fortplot_zlib_core.f90 Add safer compression subroutine with debug logging            src/external/fortplot_zlib_core.f90 Add zlib_compress_into subroutine that allocates output buffer directly Convert existing zlib_compress to wrapper calling new subroutine Add debug logging infrastructure with environment variable control Add utility functions for environment parsing and case conversion +117/-24 fortplot_zlib.f90 Export new compression subroutine in bridge module              src/external/fortplot_zlib.f90 Add zlib_compress_into to module exports Update public interface to include both old and new compression functions +3/-3
Bug fix	fortplot_png.f90 Update PNG backend to use new compression subroutine          src/backends/raster/fortplot_png.f90 Update import to use zlib_compress_into instead of zlib_compress Replace function call with subroutine call in generate_png_data +2/-2      fortplot_pdf.f90 Update PDF backend to use new compression subroutine          src/backends/vector/fortplot_pdf.f90 Update import to use zlib_compress_into instead of zlib_compress Replace function call with subroutine call in heatmap wrapper +2/-2      fortplot_pdf_io.f90 Update PDF I/O to use new compression subroutine                  src/backends/vector/fortplot_pdf_io.f90 Update import to use zlib_compress_into instead of zlib_compress Replace function call with subroutine call in write_content_object +2/-2

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[qodo-merge-pro]

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⚪	Debug info leakage Description: Debug logging prints directly to stdout via print when the environment flag is enabled, which can inadvertently expose sensitive runtime data in logs; consider routing through the project's logging facility with appropriate levels. fortplot_zlib_core.f90 [1047-1053] Referred Code subroutine log_zlib_debug(message) !! Emit debug message when instrumentation enabled character(len=*), intent(in) :: message if (is_zlib_debug_enabled()) then print '(a)', '[fortplot:zlib] '//trim(message) end if end subroutine log_zlib_debug
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PR Code Suggestions ✨

Explore these optional code suggestions:

Category	Suggestion	Impact
Possible issue	Prevent race conditions during initialization To prevent a race condition in multi-threaded environments, make the ensure_zlib_debug subroutine thread-safe by wrapping the initialization logic in an atomic block. src/external/fortplot_zlib_core.f90 [1025-1039] subroutine ensure_zlib_debug() !! Lazy initialization for instrumentation flag character(len=32) :: env_value integer :: status if (zlib_debug_initialized) return - call get_environment_variable('FORTPLOT_ZLIB_DEBUG', env_value, status=status) - if (status == 0) then - zlib_debug_enabled_state = parse_debug_env(env_value) - else - zlib_debug_enabled_state = .false. + atomic + if (.not. zlib_debug_initialized) then + call get_environment_variable('FORTPLOT_ZLIB_DEBUG', env_value, status=status) + if (status == 0) then + zlib_debug_enabled_state = parse_debug_env(env_value) + else + zlib_debug_enabled_state = .false. + end if + zlib_debug_initialized = .true. end if - zlib_debug_initialized = .true. + end atomic end subroutine ensure_zlib_debug [To ensure code accuracy, apply this suggestion manually] Suggestion importance[1-10]: 8 __ Why: The suggestion correctly identifies a potential race condition in the newly added ensure_zlib_debug subroutine, which is a significant correctness issue in multi-threaded contexts, and proposes a valid fix.	Medium
High-level	Consolidate logging into the existing module The PR adds a new debug logging system in fortplot_zlib_core.f90. It is recommended to integrate this functionality into the existing fortplot_logging module to ensure a consistent logging approach across the project. Examples: src/external/fortplot_zlib_core.f90 [987-1053] pure function to_lower_char(ch) result(lower) !! Lower-case conversion for ASCII characters character(len=1), intent(in) :: ch character(len=1) :: lower integer :: code lower = ch code = iachar(ch) if (code >= iachar('A') .and. code <= iachar('Z')) then lower = achar(code + 32) ... (clipped 57 lines) Solution Walkthrough: Before: ! in fortplot_zlib_core.f90 subroutine zlib_compress_into(...) logical :: debug_active ... debug_active = is_zlib_debug_enabled() if (debug_active) then call log_zlib_debug(...) end if ... end subroutine subroutine log_zlib_debug(message) if (is_zlib_debug_enabled()) then print '(a)', '[fortplot:zlib] '//trim(message) end if end subroutine logical function is_zlib_debug_enabled() ! reads FORTPLOT_ZLIB_DEBUG env var ... end function After: ! in fortplot_zlib_core.f90 use fortplot_logging, only: log_debug subroutine zlib_compress_into(...) ... call log_debug('[fortplot:zlib] zlib_compress_into begin...') ... end subroutine ! in fortplot_logging.f90 subroutine log_debug(message) if (is_debug_enabled()) then print '(a)', '[DEBUG] ' // trim(message) end if end subroutine logical function is_debug_enabled() ! reads a general debug env var, e.g. FORTPLOT_LOG_LEVEL ... end function Suggestion importance[1-10]: 7 __ Why: The suggestion correctly identifies the introduction of a parallel logging system and rightly proposes to integrate it with the existing fortplot_logging module for better design consistency and maintainability.	Medium
General	✅ Correctly handle empty environment variables Suggestion Impact: The commit removed the local parse_debug_env and related debug handling in this module, replacing it with shared debug utilities. This eliminates the prior behavior where an empty env var was treated as true, aligning with the suggestion’s intent. code diff: @@ -983,72 +982,5 @@ end do end function bit_reverse - pure function to_lower_char(ch) result(lower) - !! Lower-case conversion for ASCII characters - character(len=1), intent(in) :: ch - character(len=1) :: lower - integer :: code - - lower = ch - code = iachar(ch) - if (code >= iachar('A') .and. code <= iachar('Z')) then - lower = achar(code + 32) - end if - end function to_lower_char - - logical function parse_debug_env(value) - !! Interpret an environment variable as boolean - character(len=*), intent(in) :: value - character(len=:), allocatable :: trimmed - integer :: i - - trimmed = trim(adjustl(value)) - - if (len(trimmed) == 0) then - parse_debug_env = .true. - return - end if - - do i = 1, len(trimmed) - trimmed(i:i) = to_lower_char(trimmed(i:i)) - end do - - select case (trimmed) - case ('0', 'false', 'off', 'no') - parse_debug_env = .false. - case default - parse_debug_env = .true. - end select - end function parse_debug_env - - subroutine ensure_zlib_debug() - !! Lazy initialization for instrumentation flag - character(len=32) :: env_value - integer :: status - - if (zlib_debug_initialized) return - - call get_environment_variable('FORTPLOT_ZLIB_DEBUG', env_value, status=status) - if (status == 0) then - zlib_debug_enabled_state = parse_debug_env(env_value) - else - zlib_debug_enabled_state = .false. - end if - zlib_debug_initialized = .true. - end subroutine ensure_zlib_debug - - logical function is_zlib_debug_enabled() - !! Query instrumentation flag - call ensure_zlib_debug() - is_zlib_debug_enabled = zlib_debug_enabled_state - end function is_zlib_debug_enabled - - subroutine log_zlib_debug(message) - !! Emit debug message when instrumentation enabled - character(len=*), intent(in) :: message - if (is_zlib_debug_enabled()) then - print '(a)', '[fortplot:zlib] '//trim(message) - end if - end subroutine log_zlib_debug Modify the parse_debug_env function to interpret an empty environment variable value as false instead of true to follow conventional behavior. src/external/fortplot_zlib_core.f90 [1000-1023] logical function parse_debug_env(value) !! Interpret an environment variable as boolean character(len=*), intent(in) :: value character(len=:), allocatable :: trimmed integer :: i trimmed = trim(adjustl(value)) if (len(trimmed) == 0) then - parse_debug_env = .true. + parse_debug_env = .false. return end if do i = 1, len(trimmed) trimmed(i:i) = to_lower_char(trimmed(i:i)) end do select case (trimmed) case ('0', 'false', 'off', 'no') parse_debug_env = .false. case default parse_debug_env = .true. end select end function parse_debug_env [Suggestion processed] Suggestion importance[1-10]: 7 __ Why: The suggestion correctly identifies counter-intuitive behavior where an empty environment variable enables debugging, and proposes a logical fix to align with standard conventions.	Medium
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