Merge pull request #334 from fredrikekre/fe/nothing

Nothing comparison with ==/!=: also check LHS for nothing

Author: davidanthoff

src/linting/checks.jl

@@ -363,9 +363,15 @@ end
 
 function check_nothing_equality(x::EXPR, env::ExternalEnv)
     if isbinarycall(x) && length(x.args) == 3
-        if valof(x.args[1]) == "==" && valof(x.args[3]) == "nothing" && refof(x.args[3]) === getsymbols(env)[:Core][:nothing]
+        if valof(x.args[1]) == "==" && (
+                (valof(x.args[2]) == "nothing" && refof(x.args[2]) === getsymbols(env)[:Core][:nothing]) ||
+                (valof(x.args[3]) == "nothing" && refof(x.args[3]) === getsymbols(env)[:Core][:nothing])
+            )
             seterror!(x.args[1], NothingEquality)
-        elseif valof(x.args[1]) == "!=" && valof(x.args[3]) == "nothing" && refof(x.args[3]) === getsymbols(env)[:Core][:nothing]
+        elseif valof(x.args[1]) == "!=" && (
+                (valof(x.args[2]) == "nothing" && refof(x.args[2]) === getsymbols(env)[:Core][:nothing]) ||
+                (valof(x.args[3]) == "nothing" && refof(x.args[3]) === getsymbols(env)[:Core][:nothing])
+            )
             seterror!(x.args[1], NothingNotEq)
         end
     end

test/runtests.jl

@@ -300,9 +300,12 @@ f(arg) = arg
                 @test errorof(cst[4][2][3]) === nothing
             end
 
-            let cst = parse_and_pass("a == nothing")
+            for cst in parse_and_pass.(["a == nothing", "nothing == a"])
                 @test errorof(cst[1][2]) === StaticLint.NothingEquality
             end
+            for cst in parse_and_pass.(["a != nothing", "nothing != a"])
+                @test errorof(cst[1][2]) === StaticLint.NothingNotEq
+            end
 
             let cst = parse_and_pass("""
         struct Graph