Move the package library into a separate module

Hopefully this makes it a little easier for people to use in custom
shells (and anything else where it might be useful).

src/main/resources/assets/computercraft/lua/rom/modules/main/cc/require.lua

@@ -0,0 +1,121 @@
+--- This provides a pure Lua implementation of the builtin @{require} function
+-- and @{package} library.
+--
+-- Generally you do not need to use this module - it is injected into the
+-- every program's environment. However, it may be useful when building a
+-- custom shell or when running programs yourself.
+--
+-- @module cc.require
+-- @usage Construct the package and require function, and insert them into a
+-- custom environment.
+--
+--     local env = setmetatable({}, { __index = _ENV })
+--     local r = require "cc.require"
+--     env.require, env.package = r.make(env, "/")
+
+local expect = require and require("cc.expect") or dofile("rom/modules/main/cc/expect.lua")
+local expect = expect.expect
+
+local function preload(package)
+    return function(name)
+        if package.preload[name] then
+            return package.preload[name]
+        else
+            return nil, "no field package.preload['" .. name .. "']"
+        end
+    end
+end
+
+local function from_file(package, env, dir)
+    return function(name)
+        local fname = string.gsub(name, "%.", "/")
+        local sError = ""
+        for pattern in string.gmatch(package.path, "[^;]+") do
+            local sPath = string.gsub(pattern, "%?", fname)
+            if sPath:sub(1, 1) ~= "/" then
+                sPath = fs.combine(dir, sPath)
+            end
+            if fs.exists(sPath) and not fs.isDir(sPath) then
+                local fnFile, sError = loadfile(sPath, nil, env)
+                if fnFile then
+                    return fnFile, sPath
+                else
+                    return nil, sError
+                end
+            else
+                if #sError > 0 then
+                    sError = sError .. "\n  "
+                end
+                sError = sError .. "no file '" .. sPath .. "'"
+            end
+        end
+        return nil, sError
+    end
+end
+
+local function make_require(package)
+    local sentinel = {}
+    return function(name)
+        expect(1, name, "string")
+
+        if package.loaded[name] == sentinel then
+            error("loop or previous error loading module '" .. name .. "'", 0)
+        end
+
+        if package.loaded[name] then
+            return package.loaded[name]
+        end
+
+        local sError = "module '" .. name .. "' not found:"
+        for _, searcher in ipairs(package.loaders) do
+            local loader = table.pack(searcher(name))
+            if loader[1] then
+                package.loaded[name] = sentinel
+                local result = loader[1](name, table.unpack(loader, 2, loader.n))
+                if result == nil then result = true end
+
+                package.loaded[name] = result
+                return result
+            else
+                sError = sError .. "\n  " .. loader[2]
+            end
+        end
+        error(sError, 2)
+    end
+end
+
+--- Build an implementation of Lua's @{package} library, and a @{require}
+-- function to load modules within it.
+--
+-- @tparam table env The environment to load packages into.
+-- @tparam string dir The directory that relative packages are loaded from.
+-- @treturn function The new @{require} function.
+-- @treturn table The new @{package} library.
+local function make_package(env, dir)
+    expect(1, env, "table")
+    expect(2, dir, "string")
+
+    local package = {}
+    package.loaded = {
+        _G = _G,
+        bit32 = bit32,
+        coroutine = coroutine,
+        math = math,
+        package = package,
+        string = string,
+        table = table,
+    }
+    package.path = "?;?.lua;?/init.lua;/rom/modules/main/?;/rom/modules/main/?.lua;/rom/modules/main/?/init.lua"
+    if turtle then
+        package.path = package.path .. ";/rom/modules/turtle/?;/rom/modules/turtle/?.lua;/rom/modules/turtle/?/init.lua"
+    elseif commands then
+        package.path = package.path .. ";/rom/modules/command/?;/rom/modules/command/?.lua;/rom/modules/command/?/init.lua"
+    end
+    package.config = "/\n;\n?\n!\n-"
+    package.preload = {}
+    package.loaders = { preload(package), from_file(package, env, dir) }
+
+    return make_require(package), package
+end
+
+return { make = make_package }

src/main/resources/assets/computercraft/lua/rom/programs/shell.lua

@@ -11,6 +11,7 @@
 -- @module[module] shell
 
 local expect = dofile("rom/modules/main/cc/expect.lua").expect
+local make_package = dofile("rom/modules/main/cc/require.lua").make
 
 local multishell = multishell
 local parentShell = shell
@@ -28,94 +29,10 @@ local tCompletionInfo = parentShell and parentShell.getCompletionInfo() or {}
 local tProgramStack = {}
 
 local shell = {} --- @export
-local function createShellEnv(sDir)
-    local tEnv = {}
-    tEnv.shell = shell
-    tEnv.multishell = multishell
-
-    local package = {}
-    package.loaded = {
-        _G = _G,
-        bit32 = bit32,
-        coroutine = coroutine,
-        math = math,
-        package = package,
-        string = string,
-        table = table,
-    }
-    package.path = "?;?.lua;?/init.lua;/rom/modules/main/?;/rom/modules/main/?.lua;/rom/modules/main/?/init.lua"
-    if turtle then
-        package.path = package.path .. ";/rom/modules/turtle/?;/rom/modules/turtle/?.lua;/rom/modules/turtle/?/init.lua"
-    elseif commands then
-        package.path = package.path .. ";/rom/modules/command/?;/rom/modules/command/?.lua;/rom/modules/command/?/init.lua"
-    end
-    package.config = "/\n;\n?\n!\n-"
-    package.preload = {}
-    package.loaders = {
-        function(name)
-            if package.preload[name] then
-                return package.preload[name]
-            else
-                return nil, "no field package.preload['" .. name .. "']"
-            end
-        end,
-        function(name)
-            local fname = string.gsub(name, "%.", "/")
-            local sError = ""
-            for pattern in string.gmatch(package.path, "[^;]+") do
-                local sPath = string.gsub(pattern, "%?", fname)
-                if sPath:sub(1, 1) ~= "/" then
-                    sPath = fs.combine(sDir, sPath)
-                end
-                if fs.exists(sPath) and not fs.isDir(sPath) then
-                    local fnFile, sError = loadfile(sPath, nil, tEnv)
-                    if fnFile then
-                        return fnFile, sPath
-                    else
-                        return nil, sError
-                    end
-                else
-                    if #sError > 0 then
-                        sError = sError .. "\n  "
-                    end
-                    sError = sError .. "no file '" .. sPath .. "'"
-                end
-            end
-            return nil, sError
-        end,
-    }
-
-    local sentinel = {}
-    local function require(name)
-        expect(1, name, "string")
-        if package.loaded[name] == sentinel then
-            error("loop or previous error loading module '" .. name .. "'", 0)
-        end
-        if package.loaded[name] then
-            return package.loaded[name]
-        end
-
-        local sError = "module '" .. name .. "' not found:"
-        for _, searcher in ipairs(package.loaders) do
-            local loader = table.pack(searcher(name))
-            if loader[1] then
-                package.loaded[name] = sentinel
-                local result = loader[1](name, table.unpack(loader, 2, loader.n))
-                if result == nil then result = true end
-
-                package.loaded[name] = result
-                return result
-            else
-                sError = sError .. "\n  " .. loader[2]
-            end
-        end
-        error(sError, 2)
-    end
-
-    tEnv.package = package
-    tEnv.require = require
-
-    return tEnv
+local function createShellEnv(dir)
+    local env = { shell = shell, multishell = multishell }
+    env.require, env.package = make_package(env, dir)
+    return env
 end
 
 -- Colours

src/test/resources/test-rom/spec/modules/cc/shell/require_spec.lua

@@ -0,0 +1,79 @@
+describe("cc.require", function()
+    local r = require "cc.require"
+    local function mk()
+        local env = setmetatable({}, { __index = _ENV })
+        env.require, env.package = r.make({}, "/test-files/modules")
+        return env.require, env.package
+    end
+
+    local function setup(path, contents)
+        fs.delete("/test-files/modules")
+        io.open(path, "w"):write(contents):close()
+    end
+
+    describe("require", function()
+        it("errors on recursive modules", function()
+            local require, package = mk()
+            package.preload.pkg = function() require "pkg" end
+            expect.error(require, "pkg"):eq("loop or previous error loading module 'pkg'")
+        end)
+
+        it("supplies the current module name", function()
+            local require, package = mk()
+            package.preload.pkg = table.pack
+            expect(require("pkg")):same { n = 1, "pkg" }
+        end)
+
+        it("returns true instead of nil", function()
+            local require, package = mk()
+            package.preload.pkg = function() return nil end
+            expect(require("pkg")):eq(true)
+        end)
+
+        it("returns a constant value", function()
+            local require, package = mk()
+            package.preload.pkg = function() return {} end
+            expect(require("pkg")):eq(require("pkg"))
+        end)
+
+        it("returns an error on not-found modules", function()
+            local require, package = mk()
+            package.path = "/?;/?.lua"
+            expect.error(require, "pkg"):eq(
+                "module 'pkg' not found:\n" ..
+                "  no field package.preload['pkg']\n" ..
+                "  no file '/pkg'\n" ..
+                "  no file '/pkg.lua'")
+        end)
+    end)
+
+    describe("the file loader", function()
+        local function get(path)
+            local require, package = mk()
+            if path then package.path = path end
+            return require
+        end
+
+        it("works on absolute paths", function()
+            local require = get("/test-files/?.lua")
+            setup("test-files/some_module.lua", "return 123")
+            expect(require("some_module")):eq(123)
+        end)
+
+        it("works on relative paths", function()
+            local require = get("?.lua")
+            setup("test-files/modules/some_module.lua", "return 123")
+            expect(require("some_module")):eq(123)
+        end)
+
+        it("fails on syntax errors", function()
+            local require = get("?.lua")
+            setup("test-files/modules/some_module.lua", "1")
+            expect.error(require, "some_module"):str_match(
+                "^module 'some_module' not found:\n" ..
+                "  no field package.preload%['some_module'%]\n" ..
+                "  [^:]*some_module.lua:1: unexpected symbol near '1'$"
+            )
+        end)
+    end)
+end)