Work around bug where frames report lineno outside source block

stackprinter/extraction.py

@@ -95,6 +95,24 @@ def get_info(tb_or_frame, lineno=None):
         source = []
         startline = lineno
 
+    if lineno < startline:
+        # Catch an edge case where the frame's current line numer is wrong,
+        # or the discoverd line number where the frame's code block starts is.
+        # This looks like a python bug or an `inspect.getsource` bug --
+        # OR a getsource bug that is ultimately a python bug, because `inspect`
+        # just uses `frame.f_code.co_firstlineno` (= the frame's own reported
+        # beginning of its code block), and I can't imagine a situation where
+        # that can legitimately not contain `frame.f_lineno`.
+        # I deal with this here by showing a warning in-band that the line
+        # number can't be 100% trusted, while also  moving the active line shown
+        # down to the first available source line.
+        corrected_lineno = startline  # move the reported active line
+        source = ["# // Stackprinter: This frame reported a line number outside"
+                  " its reported code scope. Line %d reported, but guessing"
+                  " %d instead.\n" % (lineno, corrected_lineno)] + source
+        startline -= 1 # account for the in-band warning prepended to our source
+        lineno = corrected_lineno
+
     source_map, line2names, name2lines, head_lns, lineno = annotate(source, startline, lineno)
 
     if function in NON_FUNCTION_SCOPES: