Allow recursive def references inside def init values (#578)

Author: chrisrink10

CHANGELOG.md

@@ -9,6 +9,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  * Added support for auto-resolving namespaces for keyword from the current namespace using the `::kw` syntax (#576)
  * Added support for namespaced map syntax (#577)
 
+### Fixed
+ * Fixed a bug where `def` forms did not permit recursive references to the `def`'ed Vars (#578)
+
 ## [v0.1.dev14] - 2020-06-18
 ### Added
  * Added support for `future`s (#441)

src/basilisp/lang/compiler/analyzer.py

@@ -838,19 +838,18 @@ def _def_ast(  # pylint: disable=too-many-branches,too-many-locals
             f"def names must be symbols, not {type(name)}", form=name
         )
 
+    init_idx: Optional[int]
     children: vec.Vector[kw.Keyword]
     if nelems == 2:
-        init = None
+        init_idx = None
         doc = None
         children = vec.Vector.empty()
     elif nelems == 3:
-        with ctx.expr_pos():
-            init = _analyze_form(ctx, runtime.nth(form, 2))
+        init_idx = 2
         doc = None
         children = vec.v(INIT)
     else:
-        with ctx.expr_pos():
-            init = _analyze_form(ctx, runtime.nth(form, 3))
+        init_idx = 3
         doc = runtime.nth(form, 2)
         if not isinstance(doc, str):
             raise AnalyzerException("def docstring must be a string", form=doc)
@@ -918,6 +917,15 @@ def _def_ast(  # pylint: disable=too-many-branches,too-many-locals
         dynamic=def_meta.val_at(SYM_DYNAMIC_META_KEY, False),  # type: ignore
         meta=var_meta,
     )
+
+    # Set the value after interning the Var so the symbol is available for
+    # recursive definition.
+    if init_idx is not None:
+        with ctx.expr_pos():
+            init = _analyze_form(ctx, runtime.nth(form, init_idx))
+    else:
+        init = None
+
     descriptor = Def(
         form=form,
         name=bare_name,

tests/basilisp/compiler_test.py

@@ -288,6 +288,12 @@ def test_def_unbound(self, lcompile: CompileFn, ns: runtime.Namespace):
         assert var.root == runtime.Unbound(var)
         assert not var.is_bound
 
+    def test_recursive_def(self, lcompile: CompileFn, ns: runtime.Namespace):
+        lcompile("(def a a)")
+        var = Var.find_in_ns(sym.symbol(ns.name), sym.symbol("a"))
+        assert var.root == runtime.Unbound(var)
+        assert var.is_bound
+
     def test_def_number_of_elems(self, lcompile: CompileFn, ns: runtime.Namespace):
         with pytest.raises(compiler.CompilerException):
             lcompile("(def)")