Repository: hylang/hy (Python)

Issue:
More misplaced tracebacks
There are cases not fixed by #2423 in which position information is still set incorrectly:

```
$ echo ';;;;;;\n(do-mac (quote (raise (ValueError))))' >ex.hy
$ hy ex.hy 
Traceback (most recent call last):
  …
  File "/tmp/ex.hy", line 1, in <module>
    ;;;;;;
ValueError
```

```
$ echo ';;;;;\n(defmacro m [] (quote (do (raise (ValueError)))))\n(m)' >ex.hy                      
$ hy ex.hy
Traceback (most recent call last):
  …
  File "/tmp/ex.hy", line 1, in <module>
    ;;;;;
ValueError
```

(Note that the `do` is necessary to reproduce the bug in the second case.)

These don't look so easy to fix. I think #1951 may have been ill-advised: producing bogus default positions for models without positions leads to bugs that are harder to track down than crashes that occur immediately upon constructing the AST. But ultimately there may be no reasonable positions to assign to some dynamically generated models, in which case Python still needs something. I'm not sure.

I've opened https://github.com/pytest-dev/pytest/pull/10840 to prevent pytest from crashing on this and any other cases. (Edit: This was merged, and indeed pytest no longer seems to have those crashes.)


Discussion:

Patch:
diff --git a/NEWS.rst b/NEWS.rst
index ac9068e1f..2b48f0ae6 100644
--- a/NEWS.rst
+++ b/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)
 =============================
 
diff --git a/docs/semantics.rst b/docs/semantics.rst
index 626c091d9..1dcd5b36e 100644
--- a/docs/semantics.rst
+++ b/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.
diff --git a/hy/compiler.py b/hy/compiler.py
index a72af4204..5aaa4b1a3 100755
--- a/hy/compiler.py
+++ b/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):
diff --git a/hy/core/result_macros.py b/hy/core/result_macros.py
index c4676f796..f43bdabb3 100644
--- a/hy/core/result_macros.py
+++ b/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"
diff --git a/hy/models.py b/hy/models.py
index 23ccb6c56..ad370d3f4 100644
--- a/hy/models.py
+++ b/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,


Test patch:
diff --git a/tests/test_positions.py b/tests/test_positions.py
new file mode 100644
index 000000000..c3fc8f39d
--- /dev/null
+++ b/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