util.cache: Keep eviction candidate if callback resized to make room

Previously either the old or the new values would be rejected, even if
the cache was resized to allow more items.

spec/util_cache_spec.lua

@@ -388,5 +388,26 @@ describe("util.cache", function()
 			c:resize(3);
 			assert.same({"v5", "v4", "v3"}, vs(c));
 		end);
+
+		it("eviction stuff", function ()
+			local c;
+			c = cache.new(4, function(_k,_v)
+				if c.size < 10 then
+					c:resize(c.size*2);
+				end
+			end)
+			for i = 1,20 do
+				c:set(i,i)
+			end
+			assert.equal(16, c.size);
+			assert.is_nil(c:get(1))
+			assert.is_nil(c:get(4))
+			assert.equal(5, c:get(5))
+			assert.equal(20, c:get(20))
+			c:resize(4)
+			assert.equal(20, c:get(20))
+			assert.equal(17, c:get(17))
+			assert.is_nil(c:get(10))
+		end)
 	end);
 end);

util/cache.lua

@@ -54,12 +54,17 @@ function cache_methods:set(k, v)
 	if self._count == self.size then
 		local tail = self._tail;
 		local on_evict, evicted_key, evicted_value = self._on_evict, tail.key, tail.value;
-		if on_evict ~= nil and (on_evict == false or on_evict(evicted_key, evicted_value) == false) then
+
+		local do_evict = on_evict and on_evict(evicted_key, evicted_value);
+
+		if do_evict == false then
 			-- Cache is full, and we're not allowed to evict
 			return false;
+		elseif self._count == self.size then
+			-- Cache wasn't grown
+			_remove(self, tail);
+			self._data[evicted_key] = nil;
 		end
-		_remove(self, tail);
-		self._data[evicted_key] = nil;
 	end
 
 	m = { key = k, value = v, prev = nil, next = nil };