[ruby/prism] Use `_POSIX_MAPPED_FILES` and `_WIN32` to know if memory map interface is available in the target platform

https://github.com/ruby/prism/commit/88e2ff52d4

prism/defines.h

@@ -99,4 +99,13 @@
 #   define PM_STATIC_ASSERT(line, condition, message) typedef char PM_CONCATENATE(static_assert_, line)[(condition) ? 1 : -1]
 #endif
 
+/**
+ * In general, libc for embedded systems does not support memory-mapped files.
+ * If the target platform is POSIX or Windows, we can map a file in memory and
+ * read it in a more efficient manner.
+ */
+#if defined(_POSIX_MAPPED_FILES) || defined(_WIN32)
+#   define PRISM_HAS_MMAP
+#endif
+
 #endif

prism/templates/src/serialize.c.erb

@@ -41,9 +41,11 @@ pm_serialize_string(pm_parser_t *parser, pm_string_t *string, pm_buffer_t *buffe
             pm_buffer_append_bytes(buffer, pm_string_source(string), length);
             break;
         }
+#ifdef PRISM_HAS_MMAP
         case PM_STRING_MAPPED:
             assert(false && "Cannot serialize mapped strings.");
             break;
+#endif
     }
 }
 

prism/util/pm_string.c

@@ -102,7 +102,7 @@ pm_string_mapped_init(pm_string_t *string, const char *filepath) {
 
     *string = (pm_string_t) { .type = PM_STRING_MAPPED, .source = source, .length = (size_t) file_size };
     return true;
-#else
+#elif defined(_POSIX_MAPPED_FILES)
     // Open the file for reading
     int fd = open(filepath, O_RDONLY);
     if (fd == -1) {
@@ -135,6 +135,11 @@ pm_string_mapped_init(pm_string_t *string, const char *filepath) {
     close(fd);
     *string = (pm_string_t) { .type = PM_STRING_MAPPED, .source = source, .length = size };
     return true;
+#else
+    (void) string;
+    (void) filepath;
+    perror("pm_string_mapped_init is not implemented for this platform");
+    return false;
 #endif
 }
 
@@ -213,11 +218,13 @@ pm_string_free(pm_string_t *string) {
 
     if (string->type == PM_STRING_OWNED) {
         free(memory);
+#ifdef PRISM_HAS_MMAP
     } else if (string->type == PM_STRING_MAPPED && string->length) {
 #if defined(_WIN32)
         UnmapViewOfFile(memory);
-#else
+#elif defined(_POSIX_MAPPED_FILES)
         munmap(memory, string->length);
 #endif
+#endif /* PRISM_HAS_MMAP */
     }
 }

prism/util/pm_string.h

@@ -17,7 +17,7 @@
 // The following headers are necessary to read files using demand paging.
 #ifdef _WIN32
 #include <windows.h>
-#else
+#elif defined(_POSIX_MAPPED_FILES)
 #include <fcntl.h>
 #include <sys/mman.h>
 #include <sys/stat.h>
@@ -45,8 +45,10 @@ typedef struct {
         /** This string owns its memory, and should be freed using `pm_string_free`. */
         PM_STRING_OWNED,
 
+#ifdef PRISM_HAS_MMAP
         /** This string is a memory-mapped file, and should be freed using `pm_string_free`. */
         PM_STRING_MAPPED
+#endif
     } type;
 } pm_string_t;