Retain source and stack information for exceptions

This commit refactors the exception/error classes and their handling.
It also retains Hy source strings and their originating file information, when
available, all throughout the core parser and compiler functions.

As well, with these changes, calling code is no longer responsible for providing
source and file details to exceptions,

Closes hylang#657.

hy/_compat.py

@@ -6,7 +6,10 @@
     import __builtin__ as builtins
 except ImportError:
     import builtins  # NOQA
-import sys, keyword
+
+import sys
+import keyword
+import textwrap
 
 PY3 = sys.version_info[0] >= 3
 PY35 = sys.version_info >= (3, 5)
@@ -22,11 +25,39 @@
 long_type    = int   if PY3 else long         # NOQA
 string_types = str   if PY3 else basestring   # NOQA
 
+#
+# Inspired by the same-named `six` functions.
+#
 if PY3:
-    exec('def raise_empty(t, *args): raise t(*args) from None')
+    raise_src = textwrap.dedent('''
+    def raise_from(value, from_value):
+        try:
+            raise value from from_value
+        finally:
+            traceback = None
+    ''')
+
+    def reraise(exc_type, value, traceback=None):
+        try:
+            raise value.with_traceback(traceback)
+        finally:
+            traceback = None
+
 else:
-    def raise_empty(t, *args):
-        raise t(*args)
+    def raise_from(value, from_value=None):
+        raise value
+
+    raise_src = textwrap.dedent('''
+    def reraise(exc_type, value, traceback=None):
+        try:
+            raise exc_type, value, traceback
+        finally:
+            traceback = None
+    ''')
+
+raise_code = compile(raise_src, __file__, 'exec')
+exec(raise_code)
+
 
 def isidentifier(x):
     if x in ('True', 'False', 'None', 'print'):

hy/cmdline.py

@@ -17,8 +17,11 @@
 import astor.code_gen
 
 import hy
-from hy.lex import LexException, PrematureEndOfInput, mangle
-from hy.compiler import HyTypeError, hy_compile
+
+from hy.lex import mangle
+from hy.lex.exceptions import PrematureEndOfInput
+from hy.errors import HyLanguageError, HySyntaxError
+from hy.compiler import hy_compile
 from hy.importer import hy_eval, hy_parse, runhy
 from hy.completer import completion, Completer
 from hy.macros import macro, require
@@ -83,15 +86,11 @@ def error_handler(e, use_simple_traceback=False):
                 self.showtraceback()
 
         try:
-            try:
-                do = hy_parse(source)
-            except PrematureEndOfInput:
-                return True
-        except LexException as e:
-            if e.source is None:
-                e.source = source
-                e.filename = filename
-            error_handler(e, use_simple_traceback=True)
+            do = hy_parse(source, filename=filename)
+        except PrematureEndOfInput:
+            return True
+        except HySyntaxError as e:
+            error_handler(e, use_simple_traceback=SIMPLE_TRACEBACKS)
             return False
 
         try:
@@ -102,16 +101,13 @@ def ast_callback(main_ast, expr_ast):
                     new_ast = ast.Module(main_ast.body +
                                          [ast.Expr(expr_ast.body)])
                     print(astor.to_source(new_ast))
+
             value = hy_eval(do, self.locals, "__console__",
-                            ast_callback)
-        except HyTypeError as e:
-            if e.source is None:
-                e.source = source
-                e.filename = filename
-            error_handler(e, use_simple_traceback=SIMPLE_TRACEBACKS)
-            return False
+                            ast_callback, filename=filename, source=source)
+        except SystemExit:
+            raise
         except Exception as e:
-            error_handler(e)
+            error_handler(e, use_simple_traceback=SIMPLE_TRACEBACKS)
             return False
 
         if value is not None:
@@ -190,16 +186,17 @@ def ideas_macro(ETname):
 def pretty_error(func, *args, **kw):
     try:
         return func(*args, **kw)
-    except (HyTypeError, LexException) as e:
+    except HyLanguageError as e:
         if SIMPLE_TRACEBACKS:
             print(e, file=sys.stderr)
             sys.exit(1)
         raise
 
 
-def run_command(source):
-    tree = hy_parse(source)
-    pretty_error(hy_eval, tree, module_name="__main__")
+def run_command(source, filename=None):
+    tree = hy_parse(source, filename=filename)
+    pretty_error(hy_eval, tree, module_name="__main__", filename=filename,
+                 source=source)
     return 0
 
 
@@ -321,7 +318,7 @@ def cmdline_handler(scriptname, argv):
 
     if options.command:
         # User did "hy -c ..."
-        return run_command(options.command)
+        return run_command(options.command, filename='<string>')
 
     if options.mod:
         # User did "hy -m ..."
@@ -337,7 +334,7 @@ def cmdline_handler(scriptname, argv):
     if options.args:
         if options.args[0] == "-":
             # Read the program from stdin
-            return run_command(sys.stdin.read())
+            return run_command(sys.stdin.read(), filename='<stdin>')
 
         else:
             # User did "hy <filename>"
@@ -429,11 +426,12 @@ def hy2py_main():
 
     if options.FILE is None or options.FILE == '-':
         source = sys.stdin.read()
+        hst = pretty_error(hy_parse, source, filename='<stdin>')
     else:
         with io.open(options.FILE, 'r', encoding='utf-8') as source_file:
             source = source_file.read()
+            hst = hy_parse(source, filename=options.FILE)
 
-    hst = pretty_error(hy_parse, source)
     if options.with_source:
         # need special printing on Windows in case the
         # codepage doesn't support utf-8 characters