util: Support snakecase and kebabcase formats in transformations

doc/luasnip.txt

@@ -1,4 +1,4 @@
-*luasnip.txt*           For NeoVim 0.9-0.11           Last change: 2026 May 19
+*luasnip.txt*           For NeoVim 0.9-0.11          Last change: 2026 July 05
 
 ==============================================================================
 Table of Contents                                  *luasnip-table-of-contents*

flake.nix

@@ -94,42 +94,56 @@
           shellHook = "";
         });
 
-        test_nvim_012 = nvim_master.outputs.devShells.${pkgs.system}.default.overrideAttrs(attrs: {
-          TEST_09=false_bin;
-          TEST_012=true_bin;
-          TEST_MASTER=true_bin;
-
-          # same reasoning as in nvim_09
-          DEPS_CMAKE_FLAGS="-D USE_BUNDLED=OFF -D USE_BUNDLED_TS_PARSERS=ON";
-
-          # unset lua-path here, to make sure the global env does not leak, and
-          # prevent unset later, s.t. the lua env imported by this flake
-          # exists.
-          LUA_PATH="";
-          LUA_CPATH="";
-          PREVENT_LUA_PATH_LEAK=false_bin;
+        # the package is used here instead of the dev shell that neovim-nightly-overlay provides
+        # since, for some reason, it uses an older version of fetch-cargo-vendor-util which
+        # makes crates.io return a 403 error (https://github.com/rust-lang/crates.io/issues/13482)
+        test_nvim_012 = nvim_master.packages.${pkgs.system}.neovim-developer.overrideAttrs(attrs: {
+          nativeBuildInputs = attrs.nativeBuildInputs ++ [
+            pkgs.stylua
+            pkgs.include-what-you-use
+            pkgs.clang-tools
+          ];
 
-          # clear shellHook, it doesn't do anything we really need.
-          shellHook = "";
+          # a shell hook must be used when setting env variables when using a package derivation
+          # as a dev shell
+          shellHook = /* sh */ ''
+            export TEST_09=${false_bin};
+            export TEST_012=${true_bin};
+            export TEST_MASTER=${false_bin};
+
+            # unset lua-path here, to make sure the global env does not leak, and
+            # prevent unset later, s.t. the lua env imported by this flake
+            # exists.
+            export LUA_PATH="";
+            export LUA_CPATH="";
+            export PREVENT_LUA_PATH_LEAK=${false_bin};
+          '';
         });
 
-        test_nvim_master = nvim_master.outputs.devShells.${pkgs.system}.default.overrideAttrs(attrs: {
-          TEST_09=false_bin;
-          TEST_012=false_bin;
-          TEST_MASTER=true_bin;
-
-          # same reasoning as in nvim_09
-          DEPS_CMAKE_FLAGS="-D USE_BUNDLED=OFF -D USE_BUNDLED_TS_PARSERS=ON";
-
-          # unset lua-path here, to make sure the global env does not leak, and
-          # prevent unset later, s.t. the lua env imported by this flake
-          # exists.
-          LUA_PATH="";
-          LUA_CPATH="";
-          PREVENT_LUA_PATH_LEAK=false_bin;
+        # the package is used here instead of the dev shell that neovim-nightly-overlay provides
+        # since, for some reason, it uses an older version of fetch-cargo-vendor-util which
+        # makes crates.io return a 403 error (https://github.com/rust-lang/crates.io/issues/13482)
+        test_nvim_master = nvim_master.packages.${pkgs.system}.neovim-developer.overrideAttrs(attrs: {
+          nativeBuildInputs = attrs.nativeBuildInputs ++ [
+            pkgs.stylua
+            pkgs.include-what-you-use
+            pkgs.clang-tools
+          ];
 
-          # clear shellHook, it doesn't do anything we really need.
-          shellHook = "";
+          # a shell hook must be used when setting env variables when using a package derivation
+          # as a dev shell
+          shellHook = /* sh */ ''
+            export TEST_09=${false_bin};
+            export TEST_012=${false_bin};
+            export TEST_MASTER=${true_bin};
+
+            # unset lua-path here, to make sure the global env does not leak, and
+            # prevent unset later, s.t. the lua env imported by this flake
+            # exists.
+            export LUA_PATH="";
+            export LUA_CPATH="";
+            export PREVENT_LUA_PATH_LEAK=${false_bin};
+          '';
         });
       });
     };

lua/luasnip/util/parser/neovim_parser.lua

@@ -254,7 +254,9 @@ S.format = P.any(
 				P.token("downcase"),
 				P.token("capitalize"),
 				P.token("camelcase"),
-				P.token("pascalcase")
+				P.token("pascalcase"),
+				P.token("snakecase"),
+				P.token("kebabcase")
 			),
 			S.close
 		),

lua/luasnip/util/str.lua

@@ -267,6 +267,12 @@ local function pascalcase(str)
 	end
 	return pascalcased
 end
+local function snakecase(str)
+	return string
+		.lower(str:gsub("(%l)(%u)", "%1_%2"))
+		:gsub("(%l)%s(%l)", "%1_%2")
+		:gsub("-", "_")
+end
 
 M.vscode_string_modifiers = {
 	upcase = string.upper,
@@ -277,6 +283,10 @@ M.vscode_string_modifiers = {
 		-- same as pascalcase, but first character lowercased.
 		return pascalcase(str):gsub("^.", string.lower)
 	end,
+	snakecase = snakecase,
+	kebabcase = function(str)
+		return snakecase(str):gsub("_", "-")
+	end,
 }
 
 return M

tests/integration/parser_spec.lua

@@ -301,6 +301,8 @@ describe("Parser", function()
 			capitalize = true,
 			camelcase = true,
 			pascalcase = true,
+			snakecase = true,
+			kebabcase = true,
 		}
 
 		for modifier, modified_expected in pairs(expected_map) do
@@ -335,6 +337,8 @@ describe("Parser", function()
 		capitalize = "Test text Text",
 		camelcase = "testTextText",
 		pascalcase = "TestTextText",
+		snakecase = "test_text_text",
+		kebabcase = "test-text-text",
 	})
 
 	it("modifies invalid $0 with choice.", function()