Infer ret-tag for fn forms

infer-ret-tag-fn.patch

From 3db640efe0f312598199838a2e8fd58b358ac748 Mon Sep 17 00:00:00 2001
From: Mike Fikes <mike@fikesfarm.com>
Date: Sun, 2 Apr 2017 15:07:05 -0400
Subject: [PATCH] Infer ret-tag for fn forms

---
 src/main/clojure/cljs/analyzer.cljc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/main/clojure/cljs/analyzer.cljc b/src/main/clojure/cljs/analyzer.cljc
index 75f64f3..6dbb154 100644
--- a/src/main/clojure/cljs/analyzer.cljc
+++ b/src/main/clojure/cljs/analyzer.cljc
@@ -1337,7 +1337,7 @@
                           (analyze (assoc env :context :expr) (:init args) sym))))
           fn-var? (and (some? init-expr) (= (:op init-expr) :fn))
           tag (if fn-var?
-                (or (:ret-tag init-expr) tag)
+                (or (:ret-tag init-expr) tag (:inferred-ret-tag init-expr))
                 (or tag (:tag init-expr)))
           export-as (when-let [export-val (-> sym meta :export)]
                       (if (= true export-val) var-name export-val))
@@ -1547,6 +1547,9 @@
         js-doc       (when (true? variadic)
                        "@param {...*} var_args")
         children     (mapv :expr methods)
+        inferred-ret-tag (let [inferred-tags (map (partial infer-tag env) children)]
+                           (when (apply = inferred-tags)
+                             (first inferred-tags)))
         ast          {:op :fn
                       :env env
                       :form form
@@ -1554,6 +1557,7 @@
                       :methods methods
                       :variadic variadic
                       :tag 'function
+                      :inferred-ret-tag inferred-ret-tag
                       :recur-frames *recur-frames*
                       :loop-lets *loop-lets*
                       :jsdoc [js-doc]
-- 
2.5.4 (Apple Git-61)