Improve heuristics for finding ns form

The ns-form? function is too broad in what it accepts. For example, it
considers this to be a valid ns form:

  (let [ns (range 100)] ...)

This commit makes the function more restrictive: an ns form must now be
a top-level list that starts with the symbol ns.

Fixes #247.

Author: mainej

cljfmt/src/cljfmt/core.cljc

@@ -41,16 +41,16 @@
   (nil? (z/up* zloc)))
 
 (defn- top? [zloc]
-  (and zloc (not= (z/node zloc) (z/root zloc))))
+  (some-> zloc z/up root?))
 
-(defn- top [zloc]
+(defn- root [zloc]
   (if (root? zloc) zloc (recur (z/up zloc))))
 
 (defn- clojure-whitespace? [zloc]
   (z/whitespace? zloc))
 
 (defn- surrounding-whitespace? [zloc]
-  (and (top? (z/up zloc))
+  (and (not (top? zloc))
        (surrounding? zloc clojure-whitespace?)))
 
 (defn remove-surrounding-whitespace [form]
@@ -220,7 +220,9 @@
        (= 'ns (z/sexpr zloc))))
 
 (defn- ns-form? [zloc]
-  (some-> zloc z/down ns-token?))
+  (and (top? zloc)
+       (= (z/tag zloc) :list)
+       (some-> zloc z/down ns-token?)))
 
 (defn- indent-matches? [key sym]
   (if (symbol? sym)
@@ -334,7 +336,7 @@
       zloc)))
 
 (defn- find-namespace [zloc]
-  (some-> zloc top (z/find z/next ns-form?) z/down z/next z/sexpr))
+  (some-> zloc root (z/find z/next ns-form?) z/down z/next z/sexpr))
 
 (defn indent
   ([form]

cljfmt/test/cljfmt/core_test.cljc

@@ -281,7 +281,33 @@
           "                  (prn x)))"]
          {:indents {'thing.core/defrecord [[:inner 0]]}
           #?@(:cljs [:alias-map {"t" "thing.core"}])})
-        "applies custom indentation to namespaced defrecord"))
+        "applies custom indentation to namespaced defrecord")
+    (is (reformats-to?
+         ["(let [ns subs]"
+          "  (ns \"string\"))"
+          ""
+          "(ns thing.core)"
+          ""
+          "(defthing foo [x]"
+          "(+ x 1))"]
+         ["(let [ns subs]"
+          "  (ns \"string\"))"
+          ""
+          "(ns thing.core)"
+          ""
+          "(defthing foo [x]"
+          "  (+ x 1))"]
+         {:indents {'thing.core/defthing [[:inner 0]]
+                    'let [[:inner 0]]}
+          #?@(:cljs [:alias-map {}])})
+        "recognises the current namespace as part of a qualifed indent spec, even if preceded by a local var named ns")
+    (is (reformats-to?
+         ["(let [ns (range 10)]"
+          "  (reduce + ns"
+          "          ))"]
+         ["(let [ns (range 10)]"
+          "  (reduce + ns))"]
+         "doesn't throw with local vars named ns bound to expressions")))
 
   (testing "function #() syntax"
     (is (reformats-to?