Check for POSIX features with the build system

4 files changed, 105 insertions, 42 deletions

diff --git a/NEWS b/NEWS
index fe0d5cca..b9a34beb 100644
--- a/NEWS
+++ b/NEWS
@@ -5,6 +5,7 @@ serd (0.31.0) unstable; urgency=medium
   * Allow SERD_API to be defined by the user
   * Avoid creating test files in the current directory
   * Avoid using ASCII grave as a quote
+  * Check for POSIX features with the build system
   * Clean up code
   * Fix crash when trying to read chunks without starting
   * Fix hang when skipping an error at EOF when lax parsing
@@ -15,7 +16,7 @@ serd (0.31.0) unstable; urgency=medium
   * Replace duplicated dox_to_sphinx script with sphinxygen dependency
   * Test header for warnings more strictly
 
- -- David Robillard <d@drobilla.net>  Tue, 20 Dec 2022 12:31:33 +0000
+ -- David Robillard <d@drobilla.net>  Tue, 07 Feb 2023 23:34:12 +0000
 
 serd (0.30.16) stable; urgency=medium
 
diff --git a/meson.build b/meson.build
index de5ba40c..ddef9fe2 100644
--- a/meson.build
+++ b/meson.build
@@ -42,13 +42,6 @@ m_dep = cc.find_library('m', required: false)
 # Platform Configuration #
 ##########################
 
-platform_args = []
-if host_machine.system() in ['gnu', 'linux']
-  platform_args += [
-    '-D_POSIX_C_SOURCE=200809L',
-  ]
-endif
-
 # Use versioned name everywhere to support parallel major version installations
 if host_machine.system() == 'windows'
   if get_option('default_library') == 'both'
@@ -59,6 +52,49 @@ else
   soversion = meson.project_version().split('.')[0]
 endif
 
+# Request POSIX APIs from standard headers if necessary
+system_c_args = []
+if host_machine.system() in ['cygwin', 'gnu', 'linux']
+  system_c_args += ['-D_POSIX_C_SOURCE=200809L']
+endif
+
+# Build platform-specific configuration arguments
+platform_c_args = []
+if get_option('checks').disabled()
+  # Generic build without platform-specific features
+  platform_c_args += ['-DSERD_NO_DEFAULT_CONFIG']
+elif get_option('checks').auto()
+  # Statically detect configuration from the build environment
+  platform_c_args += system_c_args
+else
+  # Only use the features detected by the build system
+  platform_c_args += ['-DSERD_NO_DEFAULT_CONFIG'] + system_c_args
+
+  # Define HAVE_SOMETHING symbols for all detected features
+  template = '#include <@0@>\nint main(void) { @1@; }'
+  if cc.links(
+    template.format('stdio.h',
+                    'return fileno(stdin);'),
+    args: system_c_args,
+    name: 'fileno')
+    platform_c_args += ['-DHAVE_FILENO']
+  endif
+  if cc.links(
+    template.format('fcntl.h',
+                    'posix_fadvise(0, 0, 4096, POSIX_FADV_SEQUENTIAL))'),
+    args: system_c_args,
+    name: 'posix_fadvise')
+    platform_c_args += ['-DHAVE_POSIX_FADVISE']
+  endif
+  if cc.links(
+    template.format('stdlib.h',
+                    'void* mem=NULL; posix_memalign(&mem, 8U, 8U);'),
+    args: system_c_args,
+    name: 'posix_memalign')
+    platform_c_args += ['-DHAVE_POSIX_MEMALIGN']
+  endif
+endif
+
 ###########
 # Library #
 ###########
@@ -92,10 +128,10 @@ endif
 libserd = library(
   versioned_name,
   sources,
-  c_args: c_suppressions + extra_c_args + platform_args + [
+  c_args: [
     '-DSERD_INTERNAL',
     '-DSERD_VERSION="@0@"'.format(meson.project_version()),
-  ],
+  ] + c_suppressions + extra_c_args + platform_c_args,
   dependencies: m_dep,
   gnu_symbol_visibility: 'hidden',
   include_directories: include_dirs,
@@ -142,7 +178,7 @@ if not get_option('tools').disabled()
   serdi = executable(
     'serdi',
     files('src/serdi.c'),
-    c_args: c_suppressions + platform_args,
+    c_args: c_suppressions + platform_c_args,
     dependencies: serd_dep,
     install: true,
     link_args: tool_link_args,
diff --git a/meson_options.txt b/meson_options.txt
index 38bc94e3..b32b4693 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -1,6 +1,9 @@
 # Copyright 2021-2022 David Robillard <d@drobilla.net>
 # SPDX-License-Identifier: 0BSD OR ISC
 
+option('checks', type: 'feature', value: 'enabled', yield: true,
+       description: 'Check for platform-specific features')
+
 option('docs', type: 'feature', value: 'auto', yield: true,
        description: 'Build documentation')
 
diff --git a/src/serd_config.h b/src/serd_config.h
index df73522b..e54b8688 100644
--- a/src/serd_config.h
+++ b/src/serd_config.h
@@ -1,15 +1,35 @@
-// Copyright 2021-2022 David Robillard <d@drobilla.net>
+// Copyright 2021-2023 David Robillard <d@drobilla.net>
 // SPDX-License-Identifier: ISC
 
 /*
-  Configuration header that defines reasonable defaults at compile time.
-
-  This allows compile-time configuration from the command line (typically via
-  the build system) while still allowing the source to be built without any
-  configuration.  The build system can define SERD_NO_DEFAULT_CONFIG to disable
-  defaults, in which case it must define things like HAVE_FEATURE to enable
-  features.  The design here ensures that compiler warnings or
-  include-what-you-use will catch any mistakes.
+  Configuration header that defines reasonable defaults at compile-time.
+
+  This allows configuration from the command-line (usually by the build system)
+  while still allowing the code to compile "as-is" with reasonable default
+  features on supported platforms.
+
+  This system is designed so that, ideally, no command-line or build-system
+  configuration is needed, but automatic feature detection can be disabled or
+  overridden for maximum control.  It should never be necessary to edit the
+  source code to achieve a given configuration.
+
+  Usage:
+
+  - By default, features are enabled if they can be detected or assumed to be
+    available from the build environment, unless `SERD_NO_DEFAULT_CONFIG` is
+    defined, which disables everything by default.
+
+  - If a symbol like `HAVE_SOMETHING` is defined to non-zero, then the
+    "something" feature is assumed to be available.
+
+  Code rules:
+
+  - To check for a feature, this header must be included, and the symbol
+    `USE_SOMETHING` used as a boolean in an `#if` expression.
+
+  - None of the other configuration symbols described here may be used
+    directly.  In particular, this header should be the only place in the
+    source code that touches `HAVE` symbols.
 */
 
 #ifndef SERD_CONFIG_H
@@ -21,62 +41,65 @@
 #if !defined(SERD_NO_DEFAULT_CONFIG)
 
 // We need unistd.h to check _POSIX_VERSION
-#  ifndef SERD_NO_POSIX
-#    ifdef __has_include
-#      if __has_include(<unistd.h>)
-#        include <unistd.h>
-#      endif
-#    elif defined(__unix__)
+#  ifdef __has_include
+#    if __has_include(<unistd.h>)
 #      include <unistd.h>
 #    endif
+#  elif defined(__unix__)
+#    include <unistd.h>
+#  endif
+
+// Define SERD_POSIX_VERSION unconditionally for convenience
+#  if defined(_POSIX_VERSION)
+#    define SERD_POSIX_VERSION _POSIX_VERSION
+#  else
+#    define SERD_POSIX_VERSION 0
 #  endif
 
 // POSIX.1-2001: fileno()
 #  ifndef HAVE_FILENO
-#    if defined(_POSIX_VERSION) && _POSIX_VERSION >= 200112L
-#      define HAVE_FILENO
+#    if SERD_POSIX_VERSION >= 200112L || defined(_WIN32)
+#      define HAVE_FILENO 1
 #    endif
 #  endif
 
 // POSIX.1-2001: posix_fadvise()
 #  ifndef HAVE_POSIX_FADVISE
-#    ifndef __APPLE__
-#      if defined(_POSIX_VERSION) && _POSIX_VERSION >= 200112L
-#        define HAVE_POSIX_FADVISE
-#      endif
+#    if SERD__POSIX_VERSION >= 200112L && !defined(__APPLE__)
+#      define HAVE_POSIX_FADVISE 1
 #    endif
 #  endif
 
 // POSIX.1-2001: posix_memalign()
 #  ifndef HAVE_POSIX_MEMALIGN
-#    if defined(_POSIX_VERSION) && _POSIX_VERSION >= 200112L
-#      define HAVE_POSIX_MEMALIGN
+#    if SERD_POSIX_VERSION >= 200112L
+#      define HAVE_POSIX_MEMALIGN 1
 #    endif
 #  endif
 
 #endif // !defined(SERD_NO_DEFAULT_CONFIG)
 
 /*
-  Make corresponding USE_FEATURE defines based on the HAVE_FEATURE defines from
-  above or the command line.  The code checks for these using #if (not #ifdef),
-  so there will be an undefined warning if it checks for an unknown feature,
-  and this header is always required by any code that checks for features, even
-  if the build system defines them all.
+  Unconditionally define symbols like USE_SOMETHING based on HAVE_SOMETHING, if
+  it's defined.  The code checks these using #if (not #ifdef), so there will be
+  a warning if it checks for an unknown feature or doesn't include this header.
+  This header should be the only file in the source code that touches symbols
+  like HAVE_SOMETHING.
 */
 
-#ifdef HAVE_FILENO
+#if defined(HAVE_FILENO) && HAVE_FILENO
 #  define USE_FILENO 1
 #else
 #  define USE_FILENO 0
 #endif
 
-#ifdef HAVE_POSIX_FADVISE
+#if defined(HAVE_POSIX_FADVISE) && HAVE_POSIX_FADVISE
 #  define USE_POSIX_FADVISE 1
 #else
 #  define USE_POSIX_FADVISE 0
 #endif
 
-#ifdef HAVE_POSIX_MEMALIGN
+#if defined(HAVE_POSIX_MEMALIGN) && HAVE_POSIX_MEMALIGN
 #  define USE_POSIX_MEMALIGN 1
 #else
 #  define USE_POSIX_MEMALIGN 0