Unroll top-level do forms (#1061)

Fixes #1028 

`do` forms emitted by macros are still not completely unrolled.

Author: chrisrink10

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
  * The compiler will issue a warning when adding any alias that might conflict with any other alias (#1045)
+ * The compiler is now capable of unrolling top level `do` forms (not including `do` forms emitted by macros) (#1028)
 
 ### Fixed
  * Fix a bug where Basilisp did not respect the value of Python's `sys.dont_write_bytecode` flag when generating bytecode (#1054)

docs/runtime.rst

@@ -111,6 +111,27 @@ This is roughly analogous to the Java classpath in Clojure.
 These values may be set manually, but are more often configured by some project management tool such as Poetry or defined in your Python virtualenv.
 These values may also be set via :ref:`cli` arguments.
 
+Requiring Code Dynamically
+##########################
+
+The Basilisp compiler attempts to verify the existence of Vars and Python module members during its analysis phase.
+It typically does that by introspecting the runtime environment (Namespaces or Python modules).
+Requiring a namespace in a highly dynamic context (e.g. from within a function call) and then immediately attempting to reference that value prevents the compiler from verifying references (which is an error).
+
+.. code-block::
+
+   ((fn []
+     (require 'basilisp.set)
+     (basilisp.set/difference #{:b} #{:a})))
+   ;; => error occurred during macroexpansion: unable to resolve symbol 'basilisp.set/difference' in this context
+
+In such cases, it may be preferable to use :lpy:fn:`requiring-resolve` to dynamically require and resolve the Var rather than fighting the compiler:
+
+.. code-block::
+
+   ((fn []
+     ((requiring-resolve 'basilisp.set/difference) #{:b} #{:a})))  ;; => #{:b}
+
 .. _namespace_imports:
 
 Namespace Imports

src/basilisp/core.lpy

@@ -5068,7 +5068,7 @@
   .. warning::
 
      Reloading namespaces has many of the same limitations described for
-     :external:py:func:`importlib.reload_module`. Below is a non-exhaustive set of
+     :external:py:func:`importlib.reload`. Below is a non-exhaustive set of
      limitations of reloading Basilisp namespace:
 
      - Vars will be re-``def``'ed based on the current definition of the underlying

src/basilisp/lang/compiler/__init__.py

@@ -23,6 +23,7 @@
     macroexpand,
     macroexpand_1,
 )
+from basilisp.lang.compiler.constants import SpecialForm
 from basilisp.lang.compiler.exception import CompilerException, CompilerPhase  # noqa
 from basilisp.lang.compiler.generator import (
     USE_VAR_INDIRECTION,
@@ -34,6 +35,7 @@
 from basilisp.lang.compiler.generator import gen_py_ast, py_module_preamble
 from basilisp.lang.compiler.generator import statementize as _statementize
 from basilisp.lang.compiler.optimizer import PythonASTOptimizer
+from basilisp.lang.interfaces import ISeq
 from basilisp.lang.typing import CompilerOpts, ReaderForm
 from basilisp.lang.util import genname
 from basilisp.util import Maybe
@@ -148,6 +150,18 @@ def _emit_ast_string(
         runtime.add_generated_python(to_py_str(module), which_ns=ns)
 
 
+def _flatmap_forms(forms: Iterable[ReaderForm]) -> Iterable[ReaderForm]:
+    """Flatmap over an iterable of forms, unrolling any top-level `do` forms"""
+    for form in forms:
+        if isinstance(form, ISeq) and form.first == SpecialForm.DO:
+            yield from _flatmap_forms(form.rest)
+        else:
+            yield form
+
+
+_sentinel = object()
+
+
 def compile_and_exec_form(
     form: ReaderForm,
     ctx: CompilerContext,
@@ -166,34 +180,42 @@ def compile_and_exec_form(
     if not ns.module.__basilisp_bootstrapped__:
         _bootstrap_module(ctx.generator_context, ctx.py_ast_optimizer, ns)
 
-    final_wrapped_name = genname(wrapped_fn_name)
-
-    lisp_ast = analyze_form(ctx.analyzer_context, form)
-    py_ast = gen_py_ast(ctx.generator_context, lisp_ast)
-    form_ast = list(
-        map(
-            _statementize,
-            itertools.chain(
-                py_ast.dependencies,
-                [_expressionize(GeneratedPyAST(node=py_ast.node), final_wrapped_name)],
-            ),
+    last = _sentinel
+    for unrolled_form in _flatmap_forms([form]):
+        final_wrapped_name = genname(wrapped_fn_name)
+        lisp_ast = analyze_form(ctx.analyzer_context, unrolled_form)
+        py_ast = gen_py_ast(ctx.generator_context, lisp_ast)
+        form_ast = list(
+            map(
+                _statementize,
+                itertools.chain(
+                    py_ast.dependencies,
+                    [
+                        _expressionize(
+                            GeneratedPyAST(node=py_ast.node), final_wrapped_name
+                        )
+                    ],
+                ),
+            )
         )
-    )
 
-    ast_module = ast.Module(body=form_ast, type_ignores=[])
-    ast_module = ctx.py_ast_optimizer.visit(ast_module)
-    ast.fix_missing_locations(ast_module)
+        ast_module = ast.Module(body=form_ast, type_ignores=[])
+        ast_module = ctx.py_ast_optimizer.visit(ast_module)
+        ast.fix_missing_locations(ast_module)
 
-    _emit_ast_string(ns, ast_module)
+        _emit_ast_string(ns, ast_module)
 
-    bytecode = compile(ast_module, ctx.filename, "exec")
-    if collect_bytecode:
-        collect_bytecode(bytecode)
-    exec(bytecode, ns.module.__dict__)  # pylint: disable=exec-used
-    try:
-        return getattr(ns.module, final_wrapped_name)()
-    finally:
-        del ns.module.__dict__[final_wrapped_name]
+        bytecode = compile(ast_module, ctx.filename, "exec")
+        if collect_bytecode:
+            collect_bytecode(bytecode)
+        exec(bytecode, ns.module.__dict__)  # pylint: disable=exec-used
+        try:
+            last = getattr(ns.module, final_wrapped_name)()
+        finally:
+            del ns.module.__dict__[final_wrapped_name]
+
+    assert last is not _sentinel, "Must compile at least one form"
+    return last
 
 
 def _incremental_compile_module(
@@ -257,7 +279,7 @@ def compile_module(
     """
     _bootstrap_module(ctx.generator_context, ctx.py_ast_optimizer, ns)
 
-    for form in forms:
+    for form in _flatmap_forms(forms):
         nodes = gen_py_ast(
             ctx.generator_context, analyze_form(ctx.analyzer_context, form)
         )