Merge pull request #2616 from Kodiologist/pragma-hy

Add the `:hy` pragma

NEWS.rst

@@ -5,6 +5,10 @@ Unreleased
 
 Supports Python 3.9 – Python 3.x
 
+New Features
+------------------------------
+* New pragma `hy`.
+
 1.0.0 ("Afternoon Review", released 2024-09-22)
 ======================================================================
 

docs/api.rst

@@ -169,9 +169,17 @@ Fundamentals
   The effect of each pragma is locally scoped to its containing function,
   class, or comprehension form (other than ``for``), if there is one.
 
-  Only one pragma is currently implemented:
+  These pragmata are currently implemented:
 
-.. _warn-on-core-shadow:
+  - ``:hy``: Set this to a string giving a Hy version number or prefix thereof,
+    such as "1.1.0" or "1", to raise a compile-time error if the currently
+    executing version of Hy isn't at least this new. If you're writing a
+    package, you should still declare the required version of Hy in ``setup.py``
+    or ``pyproject.toml`` or whatever, because ``pip`` won't look for ``(pragma
+    :hy …)`` calls. In the future, this pragma may also switch on features of Hy
+    that were introduced in or before the given version.
+
+    .. _warn-on-core-shadow:
 
   - ``:warn-on-core-shadow``: If true (the default), :hy:func:`defmacro` and
     :hy:func:`require` will raise a warning at compile-time if you define a macro

docs/versioning.rst

@@ -4,6 +4,6 @@ Versioning and compatibility
 
 Starting with Hy 1.0.0, Hy is `semantically versioned <https://semver.org>`_. Refer to `the NEWS file <https://github.com/hylang/hy/blob/master/NEWS.rst>`_ for a summary of user-visible changes brought on by each version, and how to update your code in case of breaking changes. Be sure you're reading the version of this manual (shown at the top of each page) that matches the version of Hy you're running.
 
-Hy is tested on `all released and currently maintained versions of CPython <https://devguide.python.org/versions>`_ (on Linux, Windows, and Mac OS), and on recent versions of PyPy and Pyodide. We usually find that for Hy, unlike most Python packages, we need to change things to fully support each new 3.x release of Python. We may drop compatibility with a version of Python after the CPython guys cease maintaining it. Note that we construe such a change as non-breaking, so we won't bump Hy's major version for it. But we will at least bump the minor version, and ``python_requires`` in Hy's ``setup.py`` should prevent you from installing a Hy version that won't work with your Python version.
+Hy is tested on `all released and currently maintained versions of CPython <https://devguide.python.org/versions>`_ (on Linux, Windows, and Mac OS), and on recent versions of `PyPy <https://pypy.org>`_ and `Pyodide <https://pyodide.org>`_. We usually find that for Hy, unlike most Python packages, we need to change things to fully support each new 3.x release of Python. We may drop compatibility with a version of Python after the CPython guys cease maintaining it. Note that we construe such a change as non-breaking, so we won't bump Hy's major version for it. But we will at least bump the minor version, and ``python_requires`` in Hy's ``setup.py`` should prevent you from installing a Hy version that won't work with your Python version.
 
 Starting with Hy 1.0.0, each version of Hy also has a nickname, such as "Afternoon Review". Nicknames are used in alphabetical order, with a nickname starting with "Z" then wrapping around to "A". Nicknames are provided mostly for the amusement of the maintainer, but can be useful as a conspicuous sign that you're not using the version you expected. In code, you can get the current nickname as a string (or ``None``, for unreleased commits of Hy) with ``hy.nickname``.

hy/__init__.py

@@ -1,5 +1,9 @@
 __version__ = 'unreleased'
 nickname = None
+last_version = '1.0.0'
+  # This is used by `(pragma :hy …)` to guess whether an unreleased
+  # version of Hy is new enough. In a released version, it's simply
+  # equal to `__version__`.
 
 
 def _initialize_env_var(env_var, default_val):

hy/core/result_macros.py

@@ -11,10 +11,11 @@
 import ast
 import textwrap
 from contextlib import nullcontext
-from itertools import dropwhile
+from itertools import dropwhile, zip_longest
 
 from funcparserlib.parser import finished, forward_decl, many, maybe, oneplus, some
 
+from hy import last_version
 from hy.compat import PY3_11, PY3_12
 from hy.compiler import Result, asty, mkexpr
 from hy.errors import HyEvalError, HyInternalError, HyTypeError
@@ -165,11 +166,31 @@ def compile_inline_python(compiler, expr, root, code):
 @pattern_macro("pragma", [many(KEYWORD + FORM)])
 def compile_pragma(compiler, expr, root, kwargs):
     for kw, value in kwargs:
-        if kw == Keyword("warn-on-core-shadow"):
+
+        if kw == Keyword("hy"):
+            min_version = compiler.eval(value)
+            if not isinstance(min_version, str):
+                raise compiler._syntax_error(value, "The version given to the pragma `:hy` must be a string")
+            parts = min_version.split('.')
+            if not all(p.isdigit() for p in parts):
+                raise compiler._syntax_error(value, "The string given to the pragma `:hy` must be a dot-separated sequence of integers")
+            for have, need in zip_longest(
+                    map(int, last_version.split('.')),
+                    map(int, parts)):
+                if need is None:
+                    break
+                if have is None or have < need:
+                    raise compiler._syntax_error(kw, f"Hy version {min_version} or later required")
+                if have > need:
+                    break
+
+        elif kw == Keyword("warn-on-core-shadow"):
             compiler.local_state_stack[-1]['warn_on_core_shadow'] = (
                 bool(compiler.eval(value)))
+
         else:
             raise compiler._syntax_error(kw, f"Unknown pragma `{kw}`. Perhaps it's implemented by a newer version of Hy.")
+
     return Result()
 
 
@@ -565,17 +586,16 @@ def compile_global_or_nonlocal(compiler, expr, root, syms):
         return asty.Pass(expr)
 
     names = [mangle(s) for s in syms]
-    if root == "global":
-        ret = asty.Global(expr, names=names)
-    else:
-        ret = OuterVar(expr, compiler.scope, names)
+    ret = (asty.Global(expr, names = names)
+        if root == "global" else
+        OuterVar(expr, compiler.scope, names))
 
     try:
         compiler.scope.define_nonlocal(ret, root)
     except SyntaxError as e:
         raise compiler._syntax_error(expr, e.msg)
 
-    return ret if syms else Result()
+    return ret
 
 
 @pattern_macro("del", [many(FORM)])

tests/native_tests/other.hy

@@ -6,7 +6,27 @@
   importlib
   pydoc
   pytest
-  hy.errors [HyLanguageError])
+  hy.errors [HyLanguageError HySyntaxError])
+
+
+(defn test-pragma-hy []
+
+  (pragma :hy "1")
+  (pragma :hy "1.0")
+  (pragma :hy "1.0.0")
+  (pragma :hy "0.28.0")
+
+  (eval-when-compile (setv a-version "1.0"))
+  (pragma :hy a-version)
+
+  (defn bad [v msg]
+    (with [e (pytest.raises HySyntaxError)]
+      (hy.eval `(pragma :hy ~v)))
+    (assert (in msg e.value.msg)))
+  (bad "5" "version 5 or later required")
+  (bad "1.99.1" "version 1.99.1 or later required")
+  (bad 5 "must be a string")
+  (bad "Afternoon Review" "must be a dot-separated sequence of integers"))
 
 
 (defn test-illegal-assignments []