Reworked default values

* Better out-of-the-box behavior: commonly used feature should work without configuration. Only use default value if argument/option was not used at all.
* Add `defmode` field so that old behaviour can be used, too.

spec/default_spec.lua

@@ -4,21 +4,33 @@ describe("tests related to default values", function()
    describe("default values for arguments", function()
       it("handles default argument correctly", function()
          local parser = Parser()
-         parser:argument("foo", {
-            default = "bar"
-         })
-         local args = parser:parse({})
+         parser:argument "foo"
+            :default "bar"
+         local args = parser:parse{}
          assert.same({foo = "bar"}, args)
+         local args = parser:parse{"baz"}
+         assert.same({foo = "baz"}, args)
       end)
 
-      it("handles default multi-argument correctly", function()
+      it("handles default argument for multi-argument correctly", function()
+         local parser = Parser()
+         parser:argument("foo", {
+            args = 3,
+            default = "bar",
+            defmode = "arg"
+         })
+         local args = parser:parse{"baz"}
+         assert.same({foo = {"baz", "bar", "bar"}}, args)
+      end)
+
+      it("handles default value for multi-argument correctly", function()
          local parser = Parser()
          parser:argument("foo", {
             args = 3,
             default = "bar"
          })
-         local args = parser:parse({"baz"})
-         assert.same({foo = {"baz", "bar", "bar"}}, args)
+         local args = parser:parse{}
+         assert.same({foo = {"bar", "bar", "bar"}}, args)
       end)
 
       it("does not use default values if not needed", function()
@@ -34,29 +46,57 @@ describe("tests related to default values", function()
 
    describe("default values for options", function()
       it("handles option with default value correctly", function()
-         local parser = Parser()
-         parser:option("-f", "--foo", {
-            default = "bar"
-         })
-         local args = parser:parse({"-f"})
-         assert.same({foo = "bar"}, args)
-      end)
-
-      it("handles underused option with default value correctly", function()
          local parser = Parser()
          parser:option "-o" "--output"
-            :count(1)
             :default "a.out"
          local args = parser:parse{}
          assert.same({output = "a.out"}, args)
+         args = parser:parse{"--output", "foo.txt"}
+         assert.same({output = "foo.txt"}, args)
+         assert.has_error(function() parser:parse{"-o"} end, "too few arguments")
       end)
 
-      it("doesn't use default if option is not invoked", function()
+      it("handles option with default value for multi-argument option correctly", function()
+         local parser = Parser()
+         parser:option("-s", "--several", {
+            default = "foo",
+            args = "2-3"
+         })
+         local args = parser:parse{}
+         assert.same({several = {"foo", "foo"}}, args)
+      end)
+
+      it("handles option with default value and argument", function()
+         local parser = Parser()
+         parser:option("-o", "--output", {
+            default = "a.out",
+            defmode = "arg+count"
+         })
+         local args = parser:parse{}
+         assert.same({output = "a.out"}, args)
+         args = parser:parse{"-o"}
+         assert.same({output = "a.out"}, args)
+         args = parser:parse{"-o", "value"}
+         assert.same({output = "value"}, args)
+      end)
+
+      it("handles option with default argument correctly", function()
+         local parser = Parser()
+         parser:option "-p" "--protected"
+            :target "password"
+            :default "password"
+            :defmode "arg"
+         local args = parser:parse{"-p"}
+         assert.same({password = "password"}, args)
+      end)
+
+      it("doesn't use default argument if option is not invoked", function()
          local parser = Parser()
          parser:option("-f", "--foo", {
-            default = "bar"
+            default = "bar",
+            defmode = "arg"
          })
-         local args = parser:parse({})
+         local args = parser:parse{}
          assert.same({}, args)
       end)
 
@@ -64,7 +104,8 @@ describe("tests related to default values", function()
          local parser = Parser()
          parser:option("-f", "--foo", {
             args = 3,
-            default = "bar"
+            default = "bar",
+            defmode = "arg"
          })
          local args = parser:parse({"--foo=baz"})
          assert.same({foo = {"baz", "bar", "bar"}}, args)
@@ -74,7 +115,8 @@ describe("tests related to default values", function()
          local parser = Parser()
           parser:option("-f", "--foo", {
             args = "1-2",
-            default = "bar"
+            default = "bar",
+            defmode = "arg"
          })
          local args = parser:parse({"-f", "baz"})
          assert.same({foo = {"baz"}}, args)
@@ -84,7 +126,8 @@ describe("tests related to default values", function()
          local parser = Parser()
           parser:option("-f", "--foo", {
             count = "*",
-            default = "bar"
+            default = "bar",
+            defmode = "arg + count"
          })
          local args = parser:parse({"-f", "--foo=baz", "--foo"})
          assert.same({foo = {"bar", "baz", "bar"}}, args)