compiler: give suggestions in diagnostics for unbound variable.

This uses the Jaro-Winkler edit distance, which seemed like the best
fit for identifiers, even though it is intended for people's names.

artiq/compiler/embedding.py

@@ -11,6 +11,8 @@ from collections import OrderedDict, defaultdict
 from pythonparser import ast, algorithm, source, diagnostic, parse_buffer
 from pythonparser import lexer as source_lexer, parser as source_parser
 
+from Levenshtein import jaro_winkler
+
 from ..language import core as language_core
 from . import types, builtins, asttyped, prelude
 from .transforms import ASTTypedRewriter, Inferencer, IntMonomorphizer
@@ -224,12 +226,31 @@ class StitchingASTTypedRewriter(ASTTypedRewriter):
             # Try to find this value in the host environment and quote it.
             if node.id in self.host_environment:
                 return self.quote(self.host_environment[node.id], node.loc)
+            else:
+                suggestion = self._most_similar_ident(node.id)
+                if suggestion is not None:
+                    diag = diagnostic.Diagnostic("fatal",
+                        "name '{name}' is not bound to anything; did you mean '{suggestion}'?",
+                        {"name": node.id, "suggestion": suggestion},
+                        node.loc)
+                    self.engine.process(diag)
                 else:
                     diag = diagnostic.Diagnostic("fatal",
                         "name '{name}' is not bound to anything", {"name": node.id},
                         node.loc)
                     self.engine.process(diag)
 
+    def _most_similar_ident(self, id):
+        names = set()
+        names.update(self.host_environment.keys())
+        for typing_env in reversed(self.env_stack):
+            names.update(typing_env.keys())
+
+        sorted_names = sorted(names, key=lambda other: jaro_winkler(id, other), reverse=True)
+        if len(sorted_names) > 0:
+            if jaro_winkler(id, sorted_names[0]) > 0.0:
+                return sorted_names[0]
+
 class StitchingInferencer(Inferencer):
     def __init__(self, engine, value_map, quote):
         super().__init__(engine)

setup.py

@@ -27,7 +27,8 @@ requirements = [
     "sphinx", "sphinx-argparse", "pyserial", "numpy", "scipy",
     "python-dateutil", "prettytable", "h5py", "pydaqmx", "pyelftools",
     "quamash", "pyqtgraph", "pygit2", "aiohttp",
-    "llvmlite_artiq", "pythonparser", "lit", "OutputCheck",
+    "llvmlite_artiq", "pythonparser", "python-Levenshtein",
+    "lit", "OutputCheck",
 ]
 
 scripts = [