From 5c0c3923389df75bbf529c4a78976ee1f961fadd Mon Sep 17 00:00:00 2001
From: Kristoffer Carlsson <kristoffer.carlsson@chalmers.se>
Date: Wed, 16 Aug 2017 23:21:12 +0200
Subject: [PATCH] no longer warn in code_warntype for unused variables

---
 base/interactiveutil.jl | 25 +++++++++++++++++++++++--
 test/reflection.jl      |  5 +++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/base/interactiveutil.jl b/base/interactiveutil.jl
index 4ad8d2795ad6f..1e50a94bebbf5 100644
--- a/base/interactiveutil.jl
+++ b/base/interactiveutil.jl
@@ -347,14 +347,35 @@ problematic for performance, so the results need to be used judiciously.
 See [`@code_warntype`](@ref man-code-warntype) for more information.
 """
 function code_warntype(io::IO, f, @nospecialize(t))
+    function slots_used(ci, slotnames)
+        used = falses(length(slotnames))
+        scan_exprs!(used, ci.code)
+        return used
+    end
+
+    function scan_exprs!(used, exprs)
+        for ex in exprs
+            if isa(ex, Slot)
+                used[ex.id] = true
+            elseif isa(ex, Expr)
+                scan_exprs!(used, ex.args)
+            end
+        end
+    end
+
     emph_io = IOContext(io, :TYPEEMPHASIZE => true)
     for (src, rettype) in code_typed(f, t)
         println(emph_io, "Variables:")
         slotnames = sourceinfo_slotnames(src)
+        used_slotids = slots_used(src, slotnames)
         for i = 1:length(slotnames)
             print(emph_io, "  ", slotnames[i])
-            if isa(src.slottypes, Array)
-                show_expr_type(emph_io, src.slottypes[i], true)
+            if used_slotids[i]
+                if isa(src.slottypes, Array)
+                    show_expr_type(emph_io, src.slottypes[i], true)
+                end
+            else
+                print(emph_io, " <optimized out>")
             end
             print(emph_io, '\n')
         end
diff --git a/test/reflection.jl b/test/reflection.jl
index b77e7d4e778a8..45ae7bf78a654 100644
--- a/test/reflection.jl
+++ b/test/reflection.jl
@@ -92,6 +92,11 @@ show(iob, expand(Main, :(x -> x^2)))
 str = String(take!(iob))
 @test isempty(search(str, tag))
 
+# Make sure non used variables are not emphasized
+has_unused() = (a = rand(5))
+@test !warntype_hastag(has_unused, Tuple{}, tag)
+@test warntype_hastag(has_unused, Tuple{}, "<optimized out>")
+
 module ImportIntrinsics15819
 # Make sure changing the lookup path of an intrinsic doesn't break
 # the heuristic for type instability warning.