Fix docstring extraction

Correctly extract docstrings (and other parts) from
`function-lambda-expression`.

Closes #6

src/doctest.lisp

@@ -255,13 +255,28 @@
   (with-input-from-string (docstring (or documentation ""))
     (run-doctests docstring output)))
 
+(defun parse-lambda-body (body)
+  (values (and (stringp (car body)) (cdr body) (pop body))
+          (and (consp (car body)) (eq 'declare (caar body)) (pop body))
+          body))
+
+(defun parse-function-lambda-expression (function)
+  (multiple-value-bind (lambda-expression closure-p name) (function-lambda-expression function)
+    (declare (ignore closure-p))
+    (let ((parameters (cadr lambda-expression))
+          (lambda-body (cddr lambda-expression)))
+      (multiple-value-bind (docstring declare body) (parse-lambda-body lambda-body)
+        (values name parameters docstring declare body)))))
+
 (defun extract-function-documentation-and-name (function)
   ;; ABCL doesn't give documentation for (documentation function 'function) for all expressions.
   ;; We try function-lambda-expression too
-  (multiple-value-bind (lambda-expression closure-p name) (function-lambda-expression function)
-    (declare (ignore closure-p))
-    (values (or (documentation function 'function) (third lambda-expression))
-            (symbol-name name))))
+  (multiple-value-bind (name parameters docstring declare body) (parse-function-lambda-expression function)
+    (declare (ignore parameters declare body))
+    (values (or (documentation function 'function)
+                docstring
+                "")
+            name)))
 
 (defun test-function (function &key (output t))
   "Test-function extracts and tests code snippets in <function>'s documentation

tests/doctest.lisp

@@ -16,6 +16,39 @@
       (assert-equalp expected-output actual-output))
     (values (first result) (second result))))
 
+(defun test-parse-function-lambda-expression (function &key
+                                                         (expected-parameters nil)
+                                                         (expected-docstring nil)
+                                                         (expected-declare nil)
+                                                         (expected-body nil))
+  (multiple-value-bind (name parameters docstring declare body) (doctest::parse-function-lambda-expression function)
+    (assert-true name)
+    (assert-equalp expected-parameters parameters)
+    (assert-equalp expected-docstring docstring)
+    (assert-equalp expected-declare declare)
+    (assert-equalp expected-body body)))
+
+(define-test parse-function-lambda-expression ()
+  (test-parse-function-lambda-expression (lambda ()))
+  (test-parse-function-lambda-expression (lambda (a b))
+                                         :expected-parameters '(a b))
+  (test-parse-function-lambda-expression (lambda () "body")
+                                         :expected-body '("body"))
+  (test-parse-function-lambda-expression (lambda () (declare) "body")
+                                         :expected-declare '(declare)
+                                         :expected-body '("body"))
+  (test-parse-function-lambda-expression (lambda () "docstring" "body")
+                                         :expected-docstring "docstring"
+                                         :expected-body '("body"))
+  (test-parse-function-lambda-expression (lambda () "docstring" (declare) "body")
+                                         :expected-docstring "docstring"
+                                         :expected-declare '(declare)
+                                         :expected-body '("body"))
+  (test-parse-function-lambda-expression (lambda () (declare))
+                                         :expected-declare '(declare))
+  (test-parse-function-lambda-expression (lambda () "docstring" (declare))
+                                         :expected-docstring "docstring"
+                                         :expected-declare '(declare)))
 
 (define-test doctest ()
   ;; Test the documentation for the library itself