Single Threaded + Emscripten Support

[vincentlaucsb]

PR Summary: Emscripten + Single-Threading Support (v3.0.0)

Summary

This PR adds first-class support for threadless and Emscripten/WebAssembly targets while keeping the existing public API intact.

Goals

• Remove mmap dependency on Emscripten at compile time
• Support builds without thread libraries
• Preserve CSVReader("file.csv") ergonomics across platforms
• Improve portability and validation confidence

Key Changes

• Emscripten parser path:
  • Exclude MmapParser with compile-time guards
  • Route filename construction through stream parsing
  • Remove runtime mmap-failure behavior on wasm targets
• Threading configuration:
  • CSV_ENABLE_THREADS=0 forced on Emscripten
  • Default CSV_ENABLE_THREADS=1 elsewhere
  • Auto-disable threading when CMake cannot find thread support
• Reader internals:
  • Refactor shared stream initialization to remove duplication
  • Reuse shared init path in the Emscripten filename constructor
  • Scope owned_file_stream to Emscripten only
• Portability:
  • Remove CMAKE_CXX_STANDARD preprocessor dependency
  • Simplify C++ feature detection around __cplusplus and _MSVC_LANG
• Quality and correctness:
  • Harden streamoff to size_t conversions with checks
  • Fix CodeQL finding in pow10() via integral exponent enforcement
  • Restore important thread-safety/concurrency comments
• Workflow/security:
  • Pin setup-emsdk by commit hash
  • Add Emscripten workflow test execution via CMAKE_CROSSCOMPILING_EMULATOR=node
• Docs:
  • Update README Integration section for threading modes
  • Add non-CMake macro usage (#define CSV_ENABLE_THREADS 0)
  • Add Emscripten behavior notes

Compatibility

• No public API breakage for existing usage patterns
• Native builds still use threaded + mmap fast path when available
• Behavior changes are limited to build-time/platform path selection

Validation

• Native single-thread Release build: pass
• Native single-thread Release tests: 100% pass
• Emscripten workflow build/test validation added in this PR

Reviewer Focus

• Emscripten constructor path and parser selection
• Threading defaults and CMake fallback behavior
• Emscripten workflow run path (CMAKE_CROSSCOMPILING_EMULATOR=node)
• File I/O sizing assumptions across platforms

[codecov]

Codecov Report

❌ Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.87%. Comparing base (7577473) to head (7fa7a6a).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
include/internal/basic_csv_parser.cpp	60.00%	1 Missing and 1 partial ⚠️
include/internal/csv_reader.hpp	93.33%	0 Missing and 1 partial ⚠️
include/internal/data_type.hpp	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #301      +/-   ##
==========================================
- Coverage   90.95%   90.87%   -0.08%     
==========================================
  Files          23       23              
  Lines        1515     1513       -2     
  Branches      617      616       -1     
==========================================
- Hits         1378     1375       -3     
- Misses         42       43       +1     
  Partials       95       95              

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