Fixing the error that occurs when a failing assertion that uses the m…

…atcher `match._` tries to format that matcher into the message.

spec/formatters_spec.lua

@@ -175,6 +175,8 @@ describe("Test Formatters", function()
     local nostringformatted = assert:format({nostring, ["n"] = 1})[1]
     assert.is.same("(matcher) no.string()",
                    nostringformatted)
+    local anythingmatcherformatted = assert:format({match._, ["n"] = 1})[1]
+    assert.is.same("(matcher) _ *anything*", anythingmatcherformatted)
   end)
 
   it("checks arglist formatting", function()

spec/spies_spec.lua

@@ -65,7 +65,18 @@ describe("Tests dealing with spies", function()
       .. "      %[1%] = 'test' } } }.\n"
       .. "Expected:\n"
       .. "%(values list%) %(%(number%) 5, %(number%) 6%)")
-  end)
+    -- assertion can format the `_` anything matcher appropriately in the fail message
+    assert.error_matches(
+      function() assert.spy(s).returned_with(5, _) end,
+      "Function never returned matching arguments.\n"
+      .. "Returned %(last call if any%):\n"
+      .. "%(values list%) %(%(table: 0x%x+%) {\n"
+      .. "  %[foo%] = {\n"
+      .. "    %[bar%] = {\n"
+      .. "      %[1%] = 'test' } } }.\n"
+      .. "Expected:\n"
+      .. "%(values list%) %(%(number%) 5, %(matcher%) _ %*anything%*%)")
+  end) -- (matcher) _ *anything*
 
   it("checks called() and called_with() assertions", function()
     local s = spy.new(function() end)
@@ -97,6 +108,17 @@ describe("Tests dealing with spies", function()
       .. "      %[1%] = 'test' } } }%)\n"
       .. "Expected:\n"
       .. "%(values list%) %(%(number%) 5, %(number%) 6%)")
+    -- assertion can format the `_` anything matcher appropriately in the fail message
+    assert.error_matches(
+      function() assert.spy(s).was.called_with(5, _) end,
+      "Function was never called with matching arguments.\n"
+      .. "Called with %(last call if any%):\n"
+      .. "%(values list%) %(%(table: 0x%x+%) {\n"
+      .. "  %[foo%] = {\n"
+      .. "    %[bar%] = {\n"
+      .. "      %[1%] = 'test' } } }%)\n"
+      .. "Expected:\n"
+      .. "%(values list%) %(%(number%) 5, %(matcher%) _ %*anything%*%)")
   end)
 
   it("checks called() and called_with() assertions using refs", function()

src/formatters/init.lua

@@ -221,7 +221,7 @@ local function fmt_matcher(arg)
   for idx = 1, arg.arguments.n do
     table.insert(args, assert:format({ arg.arguments[idx], n = 1, })[1])
   end
-  return string.format("(matcher) %s%s(%s)",
+  return string.format("(matcher) " .. (arg.name == "_" and "_ *anything*" or "%s%s(%s)"),
                        not_inverted[arg.mod],
                        tostring(arg.name),
                        table.concat(args, ", "))

src/match.lua

@@ -56,7 +56,12 @@ local state_mt = {
 }
 
 local match = {
-  _ = setmetatable({mod=true, callback=function() return true end}, matcher_mt),
+  _ = setmetatable({
+    name = "_",
+    mod = true,
+    callback = function() return true end,
+    arguments = { n = 0 },
+  }, matcher_mt),
 
   state = function() return setmetatable({mod=true, tokens={}}, state_mt) end,