(core) Error explanations from friendly-traceback

Summary: Extend formula error messages with explanations from https://github.com/friendly-traceback/friendly-traceback. Only for Python 3.

Test Plan: Updated several Python tests. In general, these require separate branches for Python 2 and 3.

Reviewers: georgegevoian

Reviewed By: georgegevoian

Differential Revision: https://phab.getgrist.com/D3542

sandbox/grist/codebuilder.py

@@ -1,11 +1,14 @@
 import ast
 import contextlib
 import itertools
+import linecache
 import re
 import six
 
 import astroid
 import asttokens
+
+import friendly_errors
 import textbuilder
 import logger
 log = logger.Logger(__name__, logger.INFO)
@@ -22,6 +25,13 @@ LAZY_ARG_FUNCTIONS = {
   'PEEK': slice(0, 1),
 }
 
+
+class GristSyntaxError(SyntaxError):
+  """
+  Indicates a formula is invalid in a Grist-specific way.
+  """
+
+
 def make_formula_body(formula, default_value, assoc_value=None):
   """
   Given a formula, returns a textbuilder.Builder object suitable to be the body of a function,
@@ -46,7 +56,7 @@ def make_formula_body(formula, default_value, assoc_value=None):
 
   # Parse the formula into an abstract syntax tree (AST), catching syntax errors.
   try:
-    atok = asttokens.ASTTokens(tmp_formula.get_text(), parse=True)
+    atok = asttokens.ASTTokens(tmp_formula.get_text(), parse=True, filename=code_filename)
   except SyntaxError as e:
     return textbuilder.Text(_create_syntax_error_code(tmp_formula, formula, e))
 
@@ -91,8 +101,7 @@ def make_formula_body(formula, default_value, assoc_value=None):
     message = "No `return` statement, and the last line isn't an expression."
     if isinstance(last_statement, ast.Assign):
       message += " If you want to check for equality, use `==` instead of `=`."
-    error = SyntaxError(message,
-                        ('<string>', 1, 1, ""))
+    error = GristSyntaxError(message, ('<string>', 1, 1, ""))
     return textbuilder.Text(_create_syntax_error_code(tmp_formula, formula, error))
 
   # Apply the new set of patches to the original formula to get the real output.
@@ -129,11 +138,24 @@ def _create_syntax_error_code(builder, input_text, err):
   output_offset = output_ln.line_to_offset(err.lineno, err.offset - 1 if err.offset else 0)
   input_offset = builder.map_back_offset(output_offset)
   line, col = input_ln.offset_to_line(input_offset)
-  message = err.args[0]
   input_text_line = input_text.splitlines()[line - 1]
+
+  message = err.args[0]
+  err_type = type(err)
+  if isinstance(err, GristSyntaxError):
+    # Just use SyntaxError in the final code
+    err_type = SyntaxError
+  elif six.PY3:
+    # Add explanation from friendly-traceback.
+    # Only supported in Python 3.
+    # Not helpful for Grist-specific errors.
+    # Needs to use the source code, so save it to its source cache.
+    save_to_linecache(builder.get_text())
+    message += friendly_errors.friendly_message(err)
+
   return "%s\nraise %s(%r, ('usercode', %r, %r, %r))" % (
     textbuilder.line_start_re.sub('# ', input_text.rstrip()),
-    type(err).__name__, message, line, col + 1, input_text_line)
+    err_type.__name__, message, line, col + 1, input_text_line)
 
 #----------------------------------------------------------------------
 
@@ -299,7 +321,7 @@ class InferRecAssignment(InferenceTip):
   @classmethod
   def filter(cls, node):
     if node.name == 'rec':
-      raise SyntaxError('Grist disallows assignment to the special variable "rec"',
+      raise GristSyntaxError('Grist disallows assignment to the special variable "rec"',
           ('<string>', node.lineno, node.col_offset, ""))
 
   @classmethod
@@ -315,8 +337,8 @@ class InferRecAttrAssignment(InferenceTip):
   @classmethod
   def filter(cls, node):
     if isinstance(node.expr, astroid.nodes.Name) and node.expr.name == 'rec':
-      raise SyntaxError("You can't assign a value to a column with `=`. "
-                        "If you mean to check for equality, use `==` instead.",
+      raise GristSyntaxError("You can't assign a value to a column with `=`. "
+                             "If you mean to check for equality, use `==` instead.",
           ('<string>', node.lineno, node.col_offset, ""))
 
   @classmethod
@@ -379,3 +401,23 @@ def parse_grist_names(builder):
           parsed_names.append(make_tuple(start, end, obj.name, node.arg))
 
   return [name for name in parsed_names if name]
+
+
+code_filename = "usercode"
+
+
+def save_to_linecache(source_code):
+  """
+  Makes source code available to friendly-traceback and traceback formatting in general.
+  """
+  if six.PY3:
+    import friendly_traceback.source_cache
+
+    friendly_traceback.source_cache.cache.add(code_filename, source_code)
+  else:
+    linecache.cache[code_filename] = (
+      len(source_code),
+      None,
+      [line + '\n' for line in source_code.splitlines()],
+      code_filename,
+    )