Improve error tracebacks so that it shows the cell prompts

docs/source/whatsnew/pr/traceback-improvements.rst

@@ -0,0 +1,39 b''
+Traceback improvements
+======================
+
+Previously, error tracebacks for errors happening in code cells were showing a hash, the one used for compiling the Python AST.
+
+    In [1]: def foo():
+    ...:     return 3 / 0
+    ...:
+
+    In [2]: foo()
+    ---------------------------------------------------------------------------
+    ZeroDivisionError                         Traceback (most recent call last)
+    <ipython-input-2-c19b6d9633cf> in <module>
+    ----> 1 foo()
+
+    <ipython-input-1-1595a74c32d5> in foo()
+        1 def foo():
+    ----> 2     return 3 / 0
+        3
+
+    ZeroDivisionError: division by zero
+
+The error traceback is now correctly formatted, showing the cell number in which the error happened:
+
+    In [1]: def foo():
+    ...:     return 3 / 0
+    ...:
+
+    In [2]: foo()
+    ---------------------------------------------------------------------------
+    ZeroDivisionError                         Traceback (most recent call last)
+    In [2], in <module>
+    ----> 1 foo()
+
+    In [1], in foo()
+        1 def foo():
+    ----> 2     return 3 / 0
+
+    ZeroDivisionError: division by zero

IPython/core/compilerop.py

@@ -92,6 +92,10 b' class CachingCompiler(codeop.Compile):'
         # (otherwise we'd lose our tracebacks).
         linecache.checkcache = check_linecache_ipython
 
+        # Caching a dictionary { filename: execution_count } for nicely
+        # rendered tracebacks. The filename corresponds to the filename
+        # argument used for the builtins.compile function.
+        self._filename_map = {}
 
     def ast_parse(self, source, filename='<unknown>', symbol='exec'):
         """Parse code to an AST with the current compiler flags active.
@@ -153,6 +157,10 b' class CachingCompiler(codeop.Compile):'
             raw_code = transformed_code
 
         name = self.get_code_name(raw_code, transformed_code, number)
+
+        # Save the execution count
+        self._filename_map[name] = number
+
         entry = (
             len(transformed_code),
             time.time(),

IPython/core/ultratb.py

@@ -581,25 +581,31 b' class VerboseTB(TBTools):'
         Colors = self.Colors  # just a shorthand + quicker name lookup
         ColorsNormal = Colors.Normal  # used a lot
 
-
-
         if isinstance(frame_info, stack_data.RepeatedFrames):
             return '    %s[... skipping similar frames: %s]%s\n' % (
                 Colors.excName, frame_info.description, ColorsNormal)
 
+        file = frame_info.filename
+
+        ipinst = get_ipython()
+        if ipinst is not None and file in ipinst.compile._filename_map:
+            file = "[%s]" % ipinst.compile._filename_map[file]
+            tpl_link = "In %s%%s%s," % (Colors.filenameEm, ColorsNormal)
+        else:
+            file = util_path.compress_user(
+                py3compat.cast_unicode(file, util_path.fs_encoding)
+            )
+            tpl_link = "File %s%%s%s," % (Colors.filenameEm, ColorsNormal)
+
         indent = ' ' * INDENT_SIZE
         em_normal = '%s\n%s%s' % (Colors.valEm, indent, ColorsNormal)
-        tpl_link = '%s%%s%s' % (Colors.filenameEm, ColorsNormal)
         tpl_call = 'in %s%%s%s%%s%s' % (Colors.vName, Colors.valEm,
                                         ColorsNormal)
         tpl_call_fail = 'in %s%%s%s(***failed resolving arguments***)%s' % \
                         (Colors.vName, Colors.valEm, ColorsNormal)
-        tpl_local_var = '%s%%s%s' % (Colors.vName, ColorsNormal)
         tpl_name_val = '%%s %s= %%s%s' % (Colors.valEm, ColorsNormal)
 
-        file = frame_info.filename
-        file = py3compat.cast_unicode(file, util_path.fs_encoding)
-        link = tpl_link % util_path.compress_user(file)
+        link = tpl_link % file
         args, varargs, varkw, locals_ = inspect.getargvalues(frame_info.frame)
 
         func = frame_info.executing.code_qualname()