Add Rugged::Config#add

This method allows you to set multiple values for the same key in a
particular config, similar to `git config --add "include.path" some/path`.

For example, I have a git config with an existing `include.path` value:

```
$ cat ~/src/opensource/rugged/.git/config
[core]
        repositoryformatversion = 0
        filemode = true
        bare = false
        logallrefupdates = true
        ignorecase = true
        precomposeunicode = true
[remote "origin"]
        url = git@github.com:codenamev/rugged.git
        fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
        remote = origin
        merge = refs/heads/master
[submodule "vendor/libgit2"]
        active = true
        url = https://github.com/libgit2/libgit2.git
[include]
        path = /Users/codenamev/.gitconfig.reflow
```

With `Rugged::Config#add` I can set another value for `include.path`
without overwriting the existing value:

```
ruby -I lib -rrugged -e'\
config = Rugged::Repository.new("/Users/codenamev/src/opensource/rugged").config;
config.add("include.path", "/Users/codenamev/.gitconfig.extras");
p config.get_all("include.path")'
["/Users/codenamev/.gitconfig.reflow", "/Users/codenamev/.gitconfig.extras"]
```

References #725

README.md

@@ -553,6 +553,32 @@ repo.config['user.name'] = true
 repo.config.delete('user.name')
 ```
 
+#### Targeting a specific config file
+
+You can also target a specific config file to perform the same actions
+as above.
+
+```ruby
+# Target a specific git-config file
+config = Rugged::Config.new "absolute/path/to/file"
+
+# Read values from the above file
+repo.config['core.bare']
+```
+
+#### Working with multiple values
+
+Rugged also makes it easy to work with configurations that have multiple values
+for the same key (`multivar`s).
+
+```ruby
+# Read all values for the 'remote.origin.fetch' key
+repo.config.get_all('remote.origin.fetch')
+
+# Add a new value to the 'remote.origin.fetch' key
+repo.config.add('remote.origin.fetch', '+refs/pull/*:refs/prs/*')
+```
+
 ---
 
 ### General methods

ext/rugged/rugged_config.c

@@ -143,6 +143,53 @@ static VALUE rb_git_config_store(VALUE self, VALUE rb_key, VALUE rb_val)
 	return Qnil;
 }
 
+/*
+ *  call-seq:
+ *   cfg.add(key, value)
+ *
+ *  Store the given +value+ in the Config file, under the section
+ *  and name specified by +key+, without replacing any existing
+ *  entries. Value can be any of the following Ruby types:
+ *  +String+, +true+, +false+ and +Fixnum+.
+ *
+ *  The config file will be automatically stored to disk.
+ *
+ *    cfg.add('custom.multi.value', 'fix')
+ *    cfg.add('custom.multi.value', true)
+ *    cfg.add('custom.multi.value', 90)
+ */
+static VALUE rb_git_config_add(VALUE self, VALUE rb_key, VALUE rb_val)
+{
+	git_config *config;
+	const char *key;
+	int error;
+
+	Data_Get_Struct(self, git_config, config);
+	Check_Type(rb_key, T_STRING);
+
+	key = StringValueCStr(rb_key);
+
+	/*
+	 * "$^" is an unmatchable regexp: it will not match anything at all, so
+	 * all values will be considered new and will not replace any present value.
+	 */
+	if (RB_TYPE_P(rb_val, T_STRING)) {
+		error = git_config_set_multivar(config, key, "$^", StringValueCStr(rb_val));
+	} else if (RB_TYPE_P(rb_val, T_TRUE) || RB_TYPE_P(rb_val, T_FALSE)) {
+		error = git_config_set_multivar(config, key, "$^", (rb_val == Qtrue) ? "true" : "false");
+	} else if (FIXNUM_P(rb_val)) {
+		char str_value[32];
+		snprintf(str_value, sizeof(str_value), "%" PRId64, (int64_t)FIX2INT(rb_val));
+		error = git_config_set_multivar(config, key, "$^", str_value);
+	} else {
+		rb_raise(rb_eTypeError,
+			"Invalid value; config files can only store string, bool or int keys");
+	}
+
+	rugged_exception_check(error);
+	return Qnil;
+}
+
 /*
  *  call-seq:
  *    cfg.delete(key) -> true or false
@@ -415,6 +462,7 @@ void Init_rugged_config(void)
 
 	rb_define_method(rb_cRuggedConfig, "store", rb_git_config_store, 2);
 	rb_define_method(rb_cRuggedConfig, "[]=", rb_git_config_store, 2);
+	rb_define_method(rb_cRuggedConfig, "add", rb_git_config_add, 2);
 
 	rb_define_method(rb_cRuggedConfig, "get", rb_git_config_get, 1);
 	rb_define_method(rb_cRuggedConfig, "[]", rb_git_config_get, 1);

test/config_test.rb

@@ -85,6 +85,22 @@ def test_write_config_values
     assert_match(/value = my value/, content)
   end
 
+  def test_write_multivar_config_values
+    config = @repo.config
+    config.add('custom.multivalue', 'my value')
+    config.add('custom.multivalue', true)
+    config.add('custom.multivalue', 42)
+
+    config2 = @repo.config
+    custom_multivar = ['my value', 'true', '42']
+    assert_equal custom_multivar, config2.get_all('custom.multivalue')
+
+    content = File.read(File.join(@repo.path, 'config'))
+    assert_match(/multivalue = my value/, content)
+    assert_match(/multivalue = true/, content)
+    assert_match(/multivalue = 42/, content)
+  end
+
   def test_delete_config_values
     config = @repo.config
     config.delete('core.bare')

test/fixtures/text_file.md

@@ -418,6 +418,32 @@ repo.config['user.name'] = true
 repo.config.delete('user.name')
 ```
 
+#### Targeting a specific config file
+
+You can also target a specific config file to perform the same actions
+as above.
+
+```ruby
+# Target a specific git-config file
+config = Rugged::Config.new "absolute/path/to/file"
+
+# Read values from the above file
+repo.config['core.bare']
+```
+
+#### Working with multiple values
+
+Rugged also makes it easy to work with configurations that have multiple values
+for the same key (`multivar`s).
+
+```ruby
+# Read all values for the 'remote.origin.fetch' key
+repo.config.get_all('remote.origin.fetch')
+
+# Add a new value to the 'remote.origin.fetch' key
+repo.config.add('remote.origin.fetch', '+refs/pull/*:refs/prs/*')
+```
+
 ---
 
 ### General methods