Merge pull request #2556 from Kodiologist/misplaced-tracebacks

Fix some traceback positions

Author: Kodiologist

NEWS.rst

@@ -20,6 +20,10 @@ New Features
 * You can now set `repl-ps1` and `repl-ps2` in your `HYSTARTUP` to customize
   `sys.ps1` and `sys.ps2` for the Hy REPL.
 
+Bug Fixes
+------------------------------
+* Tracebacks now point to the correct code in more cases.
+
 0.28.0 (released 2024-01-05)
 =============================
 

docs/semantics.rst

@@ -3,7 +3,8 @@ Semantics
 ==============
 
 This chapter describes features of Hy semantics that differ from Python's and
-aren't better categorized elsewhere, such as in the chapter :doc:`macros`.
+aren't better categorized elsewhere, such as in the chapter :doc:`macros`. Each
+is a potential trap for the unwary.
 
 .. _implicit-names:
 
@@ -71,3 +72,28 @@ following:
 Why didn't the second run of ``b.hy`` print ``2``? Because ``b.hy`` was
 unchanged, so it didn't get recompiled, so its bytecode still had the old
 expansion of the macro ``m``.
+
+Traceback positioning
+---------------------
+
+When an exception results in a traceback, Python uses line and column numbers
+associated with AST nodes to point to the source code associated with the
+exception:
+
+.. code-block:: text
+
+    Traceback (most recent call last):
+      File "cinco.py", line 4, in <module>
+        find()
+      File "cinco.py", line 2, in find
+        print(chippy)
+              ^^^^^^
+    NameError: name 'chippy' is not defined
+
+This position information is stored as attributes of the AST nodes. Hy tries to
+set these attributes appropriately so that it can also produce correctly
+targeted tracebacks, but there are cases where it can't, such as when
+evaluating code that was built at runtime out of explicit calls to :ref:`model
+constructors <models>`. Python still requires line and column numbers, so Hy
+sets these to 1 as a fallback; consequently, tracebacks can point to the
+beginning of a file even though the relevant code isn't there.

hy/compiler.py

@@ -422,7 +422,7 @@ def compile(self, tree):
             # These are unexpected errors that will--hopefully--never be seen
             # by the user.
             f_exc = traceback.format_exc()
-            exc_msg = "Internal Compiler Bug 😱\n⤷ {}".format(f_exc)
+            exc_msg = "Internal Compiler Bug\n {}".format(f_exc)
             raise HyCompileError(exc_msg)
 
     def _syntax_error(self, expr, message):

hy/core/result_macros.py

@@ -135,7 +135,7 @@ def compile_eval_foo_compile(compiler, expr, root, body):
         raise HyEvalError(str(e), compiler.filename, body, compiler.source)
 
     return (
-        compiler.compile(as_model(value))
+        compiler.compile(as_model(value).replace(expr))
         if root == "do-mac"
         else compiler._compile_branch(body)
         if root == "eval-and-compile"

hy/models.py

@@ -385,12 +385,19 @@ class Sequence(Object, tuple):
     for this purpose.
     """
 
+    _extra_kwargs = ()
+
     def replace(self, other, recursive=True):
-        if recursive:
-            for x in self:
-                replace_hy_obj(x, other)
-        Object.replace(self, other)
-        return self
+        return (
+            Object.replace(
+                Object.replace(
+                    type(self)(
+                        (replace_hy_obj(x, other) for x in self),
+                        **{k: getattr(self, k) for k in self._extra_kwargs}),
+                    self),
+                other)
+            if recursive
+            else Object.replace(self, other))
 
     def __add__(self, other):
         return self.__class__(
@@ -431,6 +438,8 @@ class FComponent(Sequence):
     format spec (if any).
     """
 
+    _extra_kwargs = ("conversion",)
+
     def __new__(cls, s=None, conversion=None):
         value = super().__new__(cls, s)
         value.conversion = conversion
@@ -465,6 +474,8 @@ class FString(Sequence):
     :ivar brackets: As in :class:`hy.models.String`.
     """
 
+    _extra_kwargs = ("brackets",)
+
     def __new__(cls, s=None, brackets=None):
         value = super().__new__(
             cls,

tests/test_positions.py

@@ -0,0 +1,27 @@
+'''Check that positioning attributes for AST nodes (which Python
+ultimately uses for tracebacks) are set correctly.'''
+
+import ast
+from hy import read_many
+from hy.compiler import hy_compile
+
+
+def cpl(string):
+    '''Compile the Hy `string` and get its final body element. A
+    newline is prepended so that line 1 is guaranteed to be the wrong
+    position for generated nodes.'''
+    return hy_compile(read_many('\n' + string), __name__).body[-1]
+
+
+def test_do_mac():
+    # https://github.com/hylang/hy/issues/2424
+    x = cpl("(do-mac '9)")
+    assert isinstance(x, ast.Expr)
+    assert x.lineno == 2
+
+
+def test_defmacro_raise():
+    # https://github.com/hylang/hy/issues/2424
+    x = cpl("(defmacro m [] '(do (raise)))\n(m)")
+    assert isinstance(x, ast.Raise)
+    assert x.lineno == 3