ruby · tenderlove · Jul 17, 2025 · Jul 17, 2025
diff --git a/prism/extension.c b/prism/extension.c
@@ -994,6 +994,14 @@ profile_file(int argc, VALUE *argv, VALUE self) {
     return Qnil;
 }
 
+static int
+parse_stream_eof(void *stream) {
+    if (rb_funcall((VALUE) stream, rb_intern("eof?"), 0)) {
+        return 1;
+    }
+    return 0;
+}
+
 /**
  * An implementation of fgets that is suitable for use with Ruby IO objects.
  */
@@ -1034,7 +1042,7 @@ parse_stream(int argc, VALUE *argv, VALUE self) {
     pm_parser_t parser;
     pm_buffer_t buffer;
 
-    pm_node_t *node = pm_parse_stream(&parser, &buffer, (void *) stream, parse_stream_fgets, &options);
+    pm_node_t *node = pm_parse_stream(&parser, &buffer, (void *) stream, parse_stream_fgets, parse_stream_eof, &options);
     rb_encoding *encoding = rb_enc_find(parser.encoding->name);
 
     VALUE source = pm_source_new(&parser, encoding, options.freeze);

diff --git a/prism/prism.c b/prism/prism.c
@@ -22830,7 +22830,7 @@ pm_parse(pm_parser_t *parser) {
  * otherwise return true.
  */
 static bool
-pm_parse_stream_read(pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets) {
+pm_parse_stream_read(pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, pm_parse_stream_feof_t *stream_feof) {
 #define LINE_SIZE 4096
     char line[LINE_SIZE];
 
@@ -22866,6 +22866,12 @@ pm_parse_stream_read(pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t
                 if (strncmp(line, "__END__\r\n", 9) == 0) return false;
                 break;
         }
+
+        // All data should be read via gets.  If the string returned by gets
+        // _doesn't_ end with a newline, then we assume we hit EOF condition.
+        if (stream_feof(stream)) {
+            break;
+        }
     }
 
     return true;
@@ -22901,16 +22907,17 @@ pm_parse_stream_unterminated_heredoc_p(pm_parser_t *parser) {
  * can stream stdin in to Ruby so we need to support a streaming API.
  */
 PRISM_EXPORTED_FUNCTION pm_node_t *
-pm_parse_stream(pm_parser_t *parser, pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, const pm_options_t *options) {
+pm_parse_stream(pm_parser_t *parser, pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, pm_parse_stream_feof_t *stream_feof, const pm_options_t *options) {
     pm_buffer_init(buffer);
 
-    bool eof = pm_parse_stream_read(buffer, stream, stream_fgets);
+    bool eof = pm_parse_stream_read(buffer, stream, stream_fgets, stream_feof);
+
     pm_parser_init(parser, (const uint8_t *) pm_buffer_value(buffer), pm_buffer_length(buffer), options);
     pm_node_t *node = pm_parse(parser);
 
     while (!eof && parser->error_list.size > 0 && (parser->lex_modes.index > 0 || pm_parse_stream_unterminated_heredoc_p(parser))) {
         pm_node_destroy(parser, node);
-        eof = pm_parse_stream_read(buffer, stream, stream_fgets);
+        eof = pm_parse_stream_read(buffer, stream, stream_fgets, stream_feof);
 
         pm_parser_free(parser);
         pm_parser_init(parser, (const uint8_t *) pm_buffer_value(buffer), pm_buffer_length(buffer), options);
@@ -23002,13 +23009,13 @@ pm_serialize_parse(pm_buffer_t *buffer, const uint8_t *source, size_t size, cons
  * given stream into to the given buffer.
  */
 PRISM_EXPORTED_FUNCTION void
-pm_serialize_parse_stream(pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, const char *data) {
+pm_serialize_parse_stream(pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, pm_parse_stream_feof_t *stream_feof, const char *data) {
     pm_parser_t parser;
     pm_options_t options = { 0 };
     pm_options_read(&options, data);
 
     pm_buffer_t parser_buffer;
-    pm_node_t *node = pm_parse_stream(&parser, &parser_buffer, stream, stream_fgets, &options);
+    pm_node_t *node = pm_parse_stream(&parser, &parser_buffer, stream, stream_fgets, stream_feof, &options);
     pm_serialize_header(buffer);
     pm_serialize_content(&parser, node, buffer);
     pm_buffer_append_byte(buffer, '\0');

diff --git a/prism/prism.h b/prism/prism.h
@@ -87,17 +87,25 @@ PRISM_EXPORTED_FUNCTION pm_node_t * pm_parse(pm_parser_t *parser);
  */
 typedef char * (pm_parse_stream_fgets_t)(char *string, int size, void *stream);
 
+/**
+ * This function is used in pm_parse_stream to check whether a stream is EOF.
+ * It closely mirrors that of feof so that feof can be used as the
+ * default implementation.
+ */
+typedef int (pm_parse_stream_feof_t)(void *stream);
+
 /**
  * Parse a stream of Ruby source and return the tree.
  *
  * @param parser The parser to use.
  * @param buffer The buffer to use.
  * @param stream The stream to parse.
  * @param stream_fgets The function to use to read from the stream.
+ * @param stream_feof The function to use to determine if the stream has hit eof.
  * @param options The optional options to use when parsing.
  * @return The AST representing the source.
  */
-PRISM_EXPORTED_FUNCTION pm_node_t * pm_parse_stream(pm_parser_t *parser, pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, const pm_options_t *options);
+PRISM_EXPORTED_FUNCTION pm_node_t * pm_parse_stream(pm_parser_t *parser, pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, pm_parse_stream_feof_t *stream_feof, const pm_options_t *options);
 
 // We optionally support serializing to a binary string. For systems that don't
 // want or need this functionality, it can be turned off with the
@@ -113,7 +121,7 @@ PRISM_EXPORTED_FUNCTION pm_node_t * pm_parse_stream(pm_parser_t *parser, pm_buff
  * @param stream_fgets The function to use to read from the stream.
  * @param data The optional data to pass to the parser.
  */
-PRISM_EXPORTED_FUNCTION void pm_serialize_parse_stream(pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, const char *data);
+PRISM_EXPORTED_FUNCTION void pm_serialize_parse_stream(pm_buffer_t *buffer, void *stream, pm_parse_stream_fgets_t *stream_fgets, pm_parse_stream_feof_t *stream_feof, const char *data);
 
 /**
  * Serialize the given list of comments to the given buffer.

diff --git a/prism_compile.c b/prism_compile.c
@@ -11503,6 +11503,18 @@ pm_parse_string(pm_parse_result_t *result, VALUE source, VALUE filepath, VALUE *
     return pm_parse_process(result, node, script_lines);
 }
 
+struct rb_stdin_wrapper {
+    VALUE rb_stdin;
+    int eof_seen;
+};
+
+static int
+pm_parse_stdin_eof(void *stream)
+{
+    struct rb_stdin_wrapper * wrapped_stdin = (struct rb_stdin_wrapper *)stream;
+    return wrapped_stdin->eof_seen;
+}
+
 /**
  * An implementation of fgets that is suitable for use with Ruby IO objects.
  */
@@ -11511,7 +11523,9 @@ pm_parse_stdin_fgets(char *string, int size, void *stream)
 {
     RUBY_ASSERT(size > 0);
 
-    VALUE line = rb_funcall((VALUE) stream, rb_intern("gets"), 1, INT2FIX(size - 1));
+    struct rb_stdin_wrapper * wrapped_stdin = (struct rb_stdin_wrapper *)stream;
+
+    VALUE line = rb_funcall(wrapped_stdin->rb_stdin, rb_intern("gets"), 1, INT2FIX(size - 1));
     if (NIL_P(line)) {
         return NULL;
     }
@@ -11522,6 +11536,13 @@ pm_parse_stdin_fgets(char *string, int size, void *stream)
     memcpy(string, cstr, length);
     string[length] = '\0';
 
+    // We're reading strings from stdin via gets.  We'll assume that if the
+    // string is smaller than the requested length, and doesn't end with a
+    // newline, that we hit EOF.
+    if (length < (size - 1) && string[length - 1] != '\n') {
+        wrapped_stdin->eof_seen = 1;
+    }
+
     return string;
 }
 
@@ -11538,8 +11559,13 @@ pm_parse_stdin(pm_parse_result_t *result)
 {
     pm_options_frozen_string_literal_init(&result->options);
 
+    struct rb_stdin_wrapper wrapped_stdin = {
+        rb_stdin,
+        0
+    };
+
     pm_buffer_t buffer;
-    pm_node_t *node = pm_parse_stream(&result->parser, &buffer, (void *) rb_stdin, pm_parse_stdin_fgets, &result->options);
+    pm_node_t *node = pm_parse_stream(&result->parser, &buffer, (void *) &wrapped_stdin, pm_parse_stdin_fgets, pm_parse_stdin_eof, &result->options);
 
     // Copy the allocated buffer contents into the input string so that it gets
     // freed. At this point we've handed over ownership, so we don't need to