fix: wrong syntax error line number

plain_file.py

@@ -455,6 +455,19 @@ def process_imports(
     return required_concepts
 
 
+def normalize_line_endings(plain_source_text: str) -> str:
+    return plain_source_text.replace("\r\n", "\n").replace("\r", "\n")
+
+
+def restore_stripped_lines(plain_source_text: str, content: str) -> str:
+    stripped_source = plain_source_text.rstrip()
+    if not content or not stripped_source.endswith(content):
+        return content
+
+    stripped_line_count = stripped_source[: len(stripped_source) - len(content)].count("\n")
+    return "\n" * stripped_line_count + content
+
+
 def read_plain_source_metadata(plain_source_text):
     try:
         plain_source_obj = frontmatter.loads(plain_source_text)
@@ -490,6 +503,8 @@ def parse_plain_source(  # noqa: C901
     imported_modules: list[str],
     modules_trace: list[str],
 ) -> PlainFileParseResult:
+    plain_source_text = normalize_line_endings(plain_source_text)
+
     plain_source_obj = read_plain_source_metadata(plain_source_text)
 
     plain_source = PLAIN_SOURCE_TEMPLATE.copy()
@@ -508,7 +523,9 @@ def parse_plain_source(  # noqa: C901
 
     [_, loaded_templates] = file_utils.get_loaded_templates(template_dirs, plain_source_text)
 
-    plain_source_full_text = render_plain_source(plain_source_obj.content, loaded_templates, code_variables)
+    plain_source_content = restore_stripped_lines(plain_source_text, plain_source_obj.content)
+
+    plain_source_full_text = render_plain_source(plain_source_content, loaded_templates, code_variables)
 
     plain_file = mistletoe.Document(io.StringIO(plain_source_full_text))
 

tests/test_plainfileparser.py

@@ -36,7 +36,7 @@ def test_unknown_section():
     with pytest.raises(
         Exception,
         match=re.escape(
-            "Syntax error at line 3: Invalid specification heading (`Unknown Section:`). Allowed headings: definitions, implementation reqs, test reqs, functional specs, acceptance tests"
+            "Syntax error at line 4: Invalid specification heading (`Unknown Section:`). Allowed headings: definitions, implementation reqs, test reqs, functional specs, acceptance tests"
         ),
     ):
         plain_file.parse_plain_source(plain_source, {}, [], [], [])
@@ -50,7 +50,7 @@ def test_duplicate_section():
 """
     with pytest.raises(
         Exception,
-        match=re.escape("Syntax error at line 3: Duplicate specification heading (`definitions`)"),
+        match=re.escape("Syntax error at line 4: Duplicate specification heading (`definitions`)"),
     ):
         plain_file.parse_plain_source(plain_source, {}, [], [], [])
 
@@ -64,11 +64,48 @@ def test_invalid_top_level_element():
 """
     with pytest.raises(
         Exception,
-        match=re.escape("Syntax error at line 2: Invalid source structure  (`code block`)"),
+        match=re.escape("Syntax error at line 3: Invalid source structure  (`code block`)"),
     ):
         plain_file.parse_plain_source(plain_source, {}, [], [], [])
 
 
+def test_syntax_error_line_number_accounts_for_frontmatter():
+    plain_source = """---
+description: 'Plain file with frontmatter'
+---
+
+***definitions***
+
+***Unknown Section:***
+"""
+    with pytest.raises(
+        Exception,
+        match=re.escape("Syntax error at line 7: Invalid specification heading (`Unknown Section:`)"),
+    ):
+        plain_file.parse_plain_source(plain_source, {}, [], [], [])
+
+
+def test_syntax_error_line_number_with_windows_line_endings():
+    plain_source = (
+        "---\r\n"
+        "description: 'Plain file with frontmatter'\r\n"
+        "---\r\n"
+        "\r\n"
+        "***definitions***\r\n"
+        "\r\n"
+        "***Unknown Section:***\r\n"
+    )
+    with pytest.raises(
+        Exception,
+        match=re.escape("Syntax error at line 7: Invalid specification heading (`Unknown Section:`)"),
+    ):
+        plain_file.parse_plain_source(plain_source, {}, [], [], [])
+
+
+def test_normalize_line_endings_does_not_duplicate_newlines():
+    assert plain_file.normalize_line_endings("a\r\nb\rc\nd") == "a\nb\nc\nd"
+
+
 def test_plain_file_parser_with_comments(get_test_data_path):
     _, plain_sections, _ = plain_file.plain_file_parser(
         "plain_file_parser_with_comments.plain",
@@ -423,7 +460,7 @@ def test_acceptance_tests_top_level_rejected():
     with pytest.raises(
         PlainSyntaxError,
         match=re.escape(
-            "Syntax error at line 1: acceptance tests heading should be nested under specific functional spec."
+            "Syntax error at line 2: acceptance tests heading should be nested under specific functional spec."
         ),
     ):
         plain_file.parse_plain_source(plain_source, {}, [], [], [])