Reworked how shell creates environments. Implemented require

"shell" now runs each program in a new lua environment, instead of
sharing that lua environment between all programs launched under a one
shell. Said environment now includes an implemenation of "require" and
the "package" API, so that programs can require modules into that
environment.

This means that programs can require in libraries without polluting the
global namespace, and without breaking the virtual computer model, as
each program has it's own set of requires, which are discarded when the
program ends.

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

@@ -15,10 +15,83 @@ local tCompletionInfo = (parentShell and parentShell.getCompletionInfo()) or {}
 local tProgramStack = {}
 
 local shell = {}
-local tEnv = {
-    [ "shell" ] = shell,
-    [ "multishell" ] = multishell,
-}
+local function createShellEnv( sDir )
+    local tEnv = {}
+    tEnv[ "shell" ] = shell
+    tEnv[ "multishell" ] = multishell
+
+    local package = {}
+    package.loaded = {}
+    package.path = "?;?.lua;?/init.lua"
+    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, 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 )
+        if package.loaded[name] == sentinel then
+            error("Loop detected requiring '" .. name .. "'", 0)
+        end
+        if package.loaded[name] then
+            return package.loaded[name]
+        end
+
+        local sError = "Error loading modile '" .. name .. "':"
+        for n,searcher in ipairs(package.loaders) do
+            local loader, err = searcher(name)
+            if loader then
+                package.loaded[name] = sentinel
+                local result, err = loader( err )
+                if result ~= nil then
+                    package.loaded[name] = result
+                    return result
+                else
+                    package.loaded[name] = true
+                    return true
+                end
+            else
+                sError = sError .. "\n" .. err
+            end
+        end
+        error(sError, 2)
+    end
+
+    tEnv["package"] = package
+    tEnv["require"] = require
+
+    return tEnv
+end
 
 -- Colours
 local promptColour, textColour, bgColour
@@ -43,7 +116,8 @@ local function run( _sCommand, ... )
             end
             multishell.setTitle( multishell.getCurrent(), sTitle )
         end
-           local result = os.run( tEnv, sPath, ... )
+        local sDir = fs.getDir( sPath )
+        local result = os.run( createShellEnv( sDir ), sPath, ... )
         tProgramStack[#tProgramStack] = nil
         if multishell then
             if #tProgramStack > 0 then
@@ -325,9 +399,9 @@ if multishell then
         if sCommand then
             local sPath = shell.resolveProgram( sCommand )
             if sPath == "rom/programs/shell.lua" then
-                return multishell.launch( tEnv, sPath, table.unpack( tWords, 2 ) )
+                return multishell.launch( createShellEnv( "rom/programs" ), sPath, table.unpack( tWords, 2 ) )
             elseif sPath ~= nil then
-                return multishell.launch( tEnv, "rom/programs/shell.lua", sCommand, table.unpack( tWords, 2 ) )
+                return multishell.launch( createShellEnv( "rom/programs" ), "rom/programs/shell.lua", sCommand, table.unpack( tWords, 2 ) )
             else
                 printError( "No such program" )
             end