4 files changed, 49 insertions, 10 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0cbf3d35..798f3c5f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -48,6 +48,7 @@ Rockspec 3.0
 
 These features are only enabled if `rockspec_format = "3.0"` is set in the rockspec:
 
+* Build type `builtin` is the default if `build.type` is not specified.
 * New table `build_dependencies`: dependencies used only for running `luarocks build`
   but not when installing binary rocks.
 * New table `test_dependencies`: dependencies used only for running `luarocks test`
diff --git a/spec/build_spec.lua b/spec/build_spec.lua
index f042cbb9..b703478e 100644
--- a/spec/build_spec.lua
+++ b/spec/build_spec.lua
@@ -244,6 +244,33 @@ describe("LuaRocks build tests #integration", function()
       end)
    end)
 
+   describe("rockspec format 3.0 #rs3", function()
+      it("defaults to build.type == 'builtin'", function()
+         local rockspec = "a_rock-1.0-1.rockspec"
+         test_env.write_file(rockspec, [[
+            rockspec_format = "3.0"
+            package = "a_rock"
+            version = "1.0-1"
+            source = {
+               url = "file://]] .. testing_paths.fixtures_dir .. [[/a_rock.lua"
+            }
+            description = {
+               summary = "An example rockspec",
+            }
+            dependencies = {
+               "lua >= 5.1"
+            }
+            build = {
+               modules = {
+                  build = "a_rock.lua"
+               },
+            }
+         ]], finally)
+         assert.truthy(run.luarocks_bool("build " .. rockspec))
+         assert.is.truthy(run.luarocks("show a_rock"))
+      end)
+   end)
+
    describe("#mock external dependencies", function()
       setup(function()
          test_env.mock_server_init()
diff --git a/spec/util/test_env.lua b/spec/util/test_env.lua
index 08d5c850..0c140be7 100644
--- a/spec/util/test_env.lua
+++ b/spec/util/test_env.lua
@@ -344,12 +344,17 @@ local function download_rocks(urls, save_path)
 end
 
 --- Create a file containing a string.
--- @param path string: path to file.
+-- @param pathname string: path to file.
 -- @param str string: content of the file.
-local function write_file(path, str)
-   local file = assert(io.open(path, "w"))
+function test_env.write_file(pathname, str, finally)
+   local file = assert(io.open(pathname, "w"))
    file:write(str)
    file:close()
+   if finally then
+      finally(function()
+         os.remove(pathname)
+      end)
+   end
 end
 
 --- Create md5sum of directory structure recursively, based on filename and size
@@ -666,8 +671,8 @@ local function create_configs()
       testing_cache = test_env.testing_paths.testing_cache
    })
 
-   write_file(test_env.testing_paths.testrun_dir .. "/testing_config.lua", config_content .. " \nweb_browser = \"true\"")
-   write_file(test_env.testing_paths.testrun_dir .. "/testing_config_show_downloads.lua", config_content
+   test_env.write_file(test_env.testing_paths.testrun_dir .. "/testing_config.lua", config_content .. " \nweb_browser = \"true\"")
+   test_env.write_file(test_env.testing_paths.testrun_dir .. "/testing_config_show_downloads.lua", config_content
                   .. "show_downloads = true \n rocks_servers={\"http://luarocks.org/repositories/rocks\"}")
 
    -- testing_config_sftp.lua
@@ -691,7 +696,7 @@ local function create_configs()
       testing_cache = test_env.testing_paths.testing_cache
    })
 
-   write_file(test_env.testing_paths.testrun_dir .. "/testing_config_sftp.lua", config_content)
+   test_env.write_file(test_env.testing_paths.testrun_dir .. "/testing_config_sftp.lua", config_content)
 
    -- luacov.config
    config_content = substitute([[
@@ -710,7 +715,7 @@ local function create_configs()
       testrun_dir = test_env.testing_paths.testrun_dir
    })
 
-   write_file(test_env.testing_paths.testrun_dir .. "/luacov.config", config_content)
+   test_env.write_file(test_env.testing_paths.testrun_dir .. "/luacov.config", config_content)
 
    config_content = [[
       -- Config file of mock LuaRocks.org site for tests
@@ -720,7 +725,7 @@ local function create_configs()
          api_version = "1",
       }
    ]]
-   write_file(test_env.testing_paths.testrun_dir .. "/luarocks_site.lua", config_content)
+   test_env.write_file(test_env.testing_paths.testrun_dir .. "/luarocks_site.lua", config_content)
 end
 
 --- Remove testing directories.
diff --git a/src/luarocks/build.lua b/src/luarocks/build.lua
index fe004fb5..25e73b0d 100644
--- a/src/luarocks/build.lua
+++ b/src/luarocks/build.lua
@@ -170,8 +170,14 @@ function build.build_rockspec(rockspec_file, need_to_fetch, minimal_mode, deps_m
       return nil, err, errcode
    elseif not rockspec.build then
       return nil, "Rockspec error: build table not specified"
-   elseif not rockspec.build.type then
-      return nil, "Rockspec error: build type not specified"
+   end
+
+   if not rockspec.build.type then
+      if rockspec:format_is_at_least("3.0") then
+         rockspec.build.type = "builtin"
+      else
+         return nil, "Rockspec error: build type not specified"
+      end
    end
 
    if not build_only_deps then