yamlchan: Add libfyaml support as an alternative to libyaml

.github/workflows/cmake.yaml

@@ -16,6 +16,7 @@ jobs:
         shared_libs: [ON, OFF]
         fortran: [OFF]
         sanitizers: [OFF]
+        yaml_backend: [yaml, fyaml]
         c_flags: ['']
         include:
           # x86-64-v3 (Haswell+, 2013: AVX2/FMA) build.  Baseline x86-64
@@ -30,29 +31,47 @@ jobs:
             shared_libs: ON
             fortran: OFF
             sanitizers: OFF
+            yaml_backend: yaml
             c_flags: '-march=x86-64-v3'
           # Add a Fortran build on each platform (shared only)
           - os: ubuntu-latest
             build_type: Release
             shared_libs: ON
             fortran: ON
             sanitizers: OFF
+            yaml_backend: yaml
           - os: macos-latest
             build_type: Release
             shared_libs: ON
             fortran: ON
             sanitizers: OFF
+            yaml_backend: yaml
           # Debug builds with sanitizers
           - os: ubuntu-latest
             build_type: Debug
             shared_libs: ON
             fortran: OFF
             sanitizers: ON
+            yaml_backend: yaml
           - os: macos-latest
             build_type: Debug
             shared_libs: ON
             fortran: OFF
             sanitizers: ON
+            yaml_backend: yaml
+          # Debug builds with libfyaml
+          - os: ubuntu-latest
+            build_type: Debug
+            shared_libs: ON
+            fortran: OFF
+            sanitizers: OFF
+            yaml_backend: fyaml
+          - os: macos-latest
+            build_type: Debug
+            shared_libs: ON
+            fortran: OFF
+            sanitizers: OFF
+            yaml_backend: fyaml
 
     runs-on: ${{ matrix.os }}
 
@@ -63,11 +82,11 @@ jobs:
         if: runner.os == 'Linux'
         run: |
           sudo apt-get update
-          sudo apt-get install -y libyaml-dev gfortran libplplot-dev plplot-driver-cairo
+          sudo apt-get install -y libyaml-dev libfyaml-dev gfortran libplplot-dev plplot-driver-cairo
 
       - name: Install dependencies (macOS)
         if: runner.os == 'macOS'
-        run: brew install libyaml gcc plplot
+        run: brew install libyaml libfyaml gcc plplot
 
       - name: Configure
         run: >
@@ -76,6 +95,7 @@ jobs:
           -DBUILD_SHARED_LIBS=${{ matrix.shared_libs }}
           -DAST_BUILD_FORTRAN=${{ matrix.fortran }}
           -DAST_ENABLE_SANITIZERS=${{ matrix.sanitizers }}
+          -DAST_YAML_BACKEND=${{ matrix.yaml_backend }}
           -DAST_C_STANDARD=11
           "-DCMAKE_C_FLAGS=${{ matrix.c_flags }}"
 

CMakeLists.txt

@@ -279,19 +279,56 @@ else()
     set(HAVE_PTHREADS 0)
 endif()
 
-# YAML
+# YAML: by default try libyaml first, then libfyaml; override with AST_YAML_BACKEND
+set(AST_YAML_BACKEND "auto" CACHE STRING
+    "YAML backend: auto (try libyaml then libfyaml), yaml, or fyaml")
+
 if(AST_WITH_YAML)
-    find_library(YAML_LIBRARY NAMES yaml)
-    find_path(YAML_INCLUDE_DIR yaml.h)
-    if(YAML_LIBRARY AND YAML_INCLUDE_DIR)
-        set(HAVE_YAML 1)
-        message(STATUS "Found libyaml: ${YAML_LIBRARY}")
-    else()
-        set(HAVE_YAML 0)
-        message(STATUS "libyaml not found - building without YAML support")
+    find_package(PkgConfig QUIET)
+
+    if(NOT AST_YAML_BACKEND STREQUAL "auto" AND
+       NOT AST_YAML_BACKEND STREQUAL "yaml" AND
+       NOT AST_YAML_BACKEND STREQUAL "fyaml")
+        message(FATAL_ERROR
+            "Unknown AST_YAML_BACKEND '${AST_YAML_BACKEND}': expected auto, yaml, or fyaml")
+    endif()
+
+    if(AST_YAML_BACKEND STREQUAL "auto" OR AST_YAML_BACKEND STREQUAL "yaml")
+        find_library(YAML_LIBRARY NAMES yaml)
+        find_path(YAML_INCLUDE_DIR yaml.h)
+        if(YAML_LIBRARY AND YAML_INCLUDE_DIR)
+            set(HAVE_YAML 1)
+            message(STATUS "Found libyaml: ${YAML_LIBRARY}")
+        elseif(AST_YAML_BACKEND STREQUAL "yaml")
+            message(FATAL_ERROR "libyaml requested but not found")
+        endif()
+    endif()
+
+    if(NOT HAVE_YAML AND
+       (AST_YAML_BACKEND STREQUAL "auto" OR AST_YAML_BACKEND STREQUAL "fyaml"))
+        # Try pkg-config first; fall back to find_library/find_path.
+        if(PKG_CONFIG_FOUND)
+            pkg_check_modules(FYAML QUIET libfyaml)
+        endif()
+        if(FYAML_FOUND)
+            set(HAVE_FYAML 1)
+            message(STATUS "Found libfyaml via pkg-config: ${FYAML_LINK_LIBRARIES}")
+        else()
+            find_library(FYAML_LIBRARY NAMES fyaml)
+            find_path(FYAML_INCLUDE_DIR libfyaml.h)
+            if(FYAML_LIBRARY AND FYAML_INCLUDE_DIR)
+                set(HAVE_FYAML 1)
+                set(FYAML_LINK_LIBRARIES ${FYAML_LIBRARY})
+                set(FYAML_INCLUDE_DIRS ${FYAML_INCLUDE_DIR})
+                message(STATUS "Found libfyaml: ${FYAML_LIBRARY}")
+            elseif(AST_YAML_BACKEND STREQUAL "fyaml")
+                message(FATAL_ERROR "libfyaml requested but not found")
+            endif()
+        endif()
+    endif()
+    if(NOT HAVE_YAML AND NOT HAVE_FYAML)
+        message(STATUS "No YAML library found - building without YAML support")
     endif()
-else()
-    set(HAVE_YAML 0)
 endif()
 
 # External PAL
@@ -736,7 +773,9 @@ if(HAVE_PTHREADS)
     target_compile_definitions(ast PRIVATE THREAD_SAFE)
 endif()
 if(HAVE_YAML)
-    target_compile_definitions(ast PRIVATE YAML)
+    target_compile_definitions(ast PRIVATE YAML "YAML_BACKEND=\"libyaml\"")
+elseif(HAVE_FYAML)
+    target_compile_definitions(ast PRIVATE FYAML "YAML_BACKEND=\"libfyaml\"")
 endif()
 if(AST_WITH_MEMDEBUG)
     target_compile_definitions(ast PRIVATE MEM_DEBUG)
@@ -767,6 +806,9 @@ endif()
 if(HAVE_YAML)
     target_link_libraries(ast PRIVATE ${YAML_LIBRARY})
     target_include_directories(ast PRIVATE ${YAML_INCLUDE_DIR})
+elseif(HAVE_FYAML)
+    target_link_libraries(ast PRIVATE ${FYAML_LINK_LIBRARIES})
+    target_include_directories(ast PRIVATE ${FYAML_INCLUDE_DIRS})
 endif()
 if(AST_WITH_EXTERNAL_PAL)
     target_link_libraries(ast PRIVATE ${PAL_LIBRARY})

Makefile.am

@@ -230,6 +230,7 @@ AST_H_FILES = \
                    src/stcobsdatalocation.h \
              src/timeframe.h \
        src/channel.h \
+          src/yaml_backend.h \
           src/yamlchan.h \
           src/fitschan.h \
           src/mocchan.h \
@@ -658,11 +659,9 @@ stardocs_DATA = @STAR_LATEX_DOCUMENTATION@
 dist_starnews_DATA = ast.news
 dist_pkgdata_DATA = COPYING
 
-if !NOYAML
-yaml = -DYAML
-else
-yaml =
-endif
+# -DYAML or -DFYAML (or empty), depending on which backend AST_CHECK_YAML
+# selected; this is the macro yaml_backend.h switches on.
+yaml = @AST_YAML_DEFINE@
 
 if !NOTHREADS
 threadsafe = -DTHREAD_SAFE

ast_tester/CMakeLists.txt

@@ -456,14 +456,26 @@ if(AST_ENABLE_HUGE_TEST)
 endif()
 
 # --- Conditional tests ---
+# testyamlchan is always built; it skips YAML tests at runtime when no backend
+# is compiled in, so that the test suite still runs clean without YAML support.
+foreach(_f imaging_wcs.asdf rotate_seq3d_cartesian.asdf tanSipWcs.txt lsst_wcs.txt)
+    configure_file("${CMAKE_CURRENT_SOURCE_DIR}/${_f}"
+                   "${CMAKE_CURRENT_BINARY_DIR}/${_f}" COPYONLY)
+endforeach()
+ast_add_test(testyamlchan)
 if(HAVE_YAML)
-    # Input data files read by the round-trip tests (the .asdf/.yaml files
-    # written by the test are created in the working directory at run time).
-    configure_file(imaging_wcs.asdf "${CMAKE_CURRENT_BINARY_DIR}/imaging_wcs.asdf" COPYONLY)
-    configure_file(tanSipWcs.txt "${CMAKE_CURRENT_BINARY_DIR}/tanSipWcs.txt" COPYONLY)
-    configure_file(lsst_wcs.txt "${CMAKE_CURRENT_BINARY_DIR}/lsst_wcs.txt" COPYONLY)
-    configure_file(rotate_seq3d_cartesian.asdf "${CMAKE_CURRENT_BINARY_DIR}/rotate_seq3d_cartesian.asdf" COPYONLY)
-    ast_add_test(testyamlchan)
+    target_compile_definitions(testyamlchan PRIVATE YAML "YAML_BACKEND=\"libyaml\"")
+elseif(HAVE_FYAML)
+    target_compile_definitions(testyamlchan PRIVATE FYAML "YAML_BACKEND=\"libfyaml\"")
+endif()
+# Run testyamlchan with LeakSanitizer enabled (overriding the suite-wide
+# detect_leaks=0) so real leaks in the YAML read/write path are caught. The
+# libfyaml backend has a known upstream leak on tagged events (in versions
+# <0.9); libfyaml.supp suppresses just that, so genuine leaks still surface.
+# LeakSanitizer only works on Linux.
+if(AST_ENABLE_SANITIZERS AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
+    set_tests_properties(testyamlchan PROPERTIES ENVIRONMENT
+        "ASAN_OPTIONS=detect_leaks=1;LSAN_OPTIONS=suppressions=${CMAKE_CURRENT_SOURCE_DIR}/libfyaml.supp")
 endif()
 
 if(HAVE_PTHREADS)

ast_tester/libfyaml.supp

@@ -0,0 +1,13 @@
+# LeakSanitizer suppressions for the libfyaml YAML backend.
+#
+# libfyaml<0.9 leaks the malloc'd buffer backing a tag token whenever an emitted
+# event carries a tag. See the analysis in
+#   https://github.com/Starlink/ast/pull/67#issuecomment-4970509982
+# Fixed upstream in
+#   https://github.com/pantoniou/libfyaml/commit/115365e1600b2c11d7cb94d59ca72586a990cdae
+#
+# The system library is stripped of its internal symbols, so the deepest named
+# frame is the exported fy_emit_event_vcreate(). Matching on it is reasonably
+# safe: AST's own allocations never pass through libfyaml's event creation,
+# so this cannot hide a genuine AST leak.
+leak:fy_emit_event_vcreate