local_fs_map for DAP

On DAP via TCP/IP connection, all the source code are detected
as remote files (without `localfs:true` in launch.json for VSCode).
In this case, DAP clients (VSCode, ...) receive the contents
of the file from DAP server and open an editor window in readonly mode.

`local_fs_map` configuration can set remote->local path translation.

For example,

```
RUBY_DEBUG_LOCAL_FS_MAP=/remote/src/:/local/src/ rdbg -O --port=...
```

On this case, if remote path is `/remote/src/is/foo.rb`, then DAP
returns `/local/src/is/foo.rb` and open the local file as writable
mode.

You can specify multiple path maps with ',' character like

```
RUBY_DEBUG_LOCAL_FS_MAP=/r1/:/l1/,/r2/:/l2/ ...
```

and also you can specify this map within launch.json for VSCode like:

```
        {
            "type": "rdbg",
            "name": "Attach with rdbg (TCP/IP 12345)",
            "request": "attach",
            "debugPort": "localhost:12345",
            "localfsMap": "/remote/src/:/local/src/"
        }
```

If both are provided, launch.json setting is used.

fix #463
fix ruby/vscode-rdbg#32

Author: ko1

lib/debug/config.rb

@@ -42,6 +42,7 @@ module DEBUGGER__
     host:           ['RUBY_DEBUG_HOST',         "REMOTE: TCP/IP remote debugging: host", :string, "127.0.0.1"],
     sock_path:      ['RUBY_DEBUG_SOCK_PATH',    "REMOTE: UNIX Domain Socket remote debugging: socket path"],
     sock_dir:       ['RUBY_DEBUG_SOCK_DIR',     "REMOTE: UNIX Domain Socket remote debugging: socket directory"],
+    local_fs_map:   ['RUBY_DEBUG_LOCAL_FS_MAP', "REMOTE: Specify local fs map", :path_map],
     cookie:         ['RUBY_DEBUG_COOKIE',       "REMOTE: Cookie for negotiation"],
     open_frontend:  ['RUBY_DEBUG_OPEN_FRONTEND',"REMOTE: frontend used by open command (vscode, chrome, default: rdbg)."],
     chrome_path:    ['RUBY_DEBUG_CHROME_PATH',  "REMOTE: Platform dependent path of Chrome (For more information, See [here](https://github.com/ruby/debug/pull/334/files#diff-5fc3d0a901379a95bc111b86cf0090b03f857edfd0b99a0c1537e26735698453R55-R64))"],
@@ -238,6 +239,8 @@ def self.parse_config_value name, valstr
             e
           end
         }
+      when :path_map
+        valstr.split(',').map{|e| e.split(':')}
       else
         valstr
       end
@@ -384,6 +387,8 @@ def self.config_to_env_hash config
           case CONFIG_SET[key][2]
           when :path
             valstr = config[key].map{|e| e.kind_of?(Regexp) ? e.inspect : e}.join(':')
+          when :path_map
+            valstr = config[key].map{|e| e.join(':')}.join(',')
           else
             valstr = config[key].to_s
           end

lib/debug/server_dap.rb

@@ -70,14 +70,39 @@ def show_protocol dir, msg
       end
     end
 
-    @local_fs = false
+    # true: all localfs
+    # Array: part of localfs
+    # nil: no localfs
+    @local_fs_map = nil
+
+    def self.local_fs_map_path path
+      case @local_fs_map
+      when nil
+        false
+      when true
+        path
+      else # Array
+        @local_fs_map.each do |(remote_path_prefix, local_path_prefix)|
+          if path.start_with? remote_path_prefix
+            return path.sub(remote_path_prefix){ local_path_prefix }
+          end
+        end
 
-    def self.local_fs
-      @local_fs
+        nil
+      end
     end
 
-    def self.local_fs_set
-      @local_fs = true
+    def self.local_fs_map_set map
+      return if @local_fs_map # already setup
+
+      case map
+      when String
+        @local_fs_map = map.split(',').map{|e| e.split(':')}
+      when true
+        @local_fs_map = map
+      when nil
+        @local_fs_map = CONFIG[:local_fs_map]
+      end
     end
 
     def dap_setup bytes
@@ -86,7 +111,7 @@ def dap_setup bytes
 
       case self
       when UI_UnixDomainServer
-        UI_DAP.local_fs_set
+        UI_DAP.local_fs_map_set true
       when UI_TcpServer
         # TODO: loopback address can be used to connect other FS env, like Docker containers
         # UI_DAP.local_fs_set if @local_addr.ipv4_loopback? || @local_addr.ipv6_loopback?
@@ -228,12 +253,12 @@ def process
         when 'launch'
           send_response req
           @is_attach = false
-          UI_DAP.local_fs_set if req.dig('arguments', 'localfs')
+          UI_DAP.local_fs_map_set req.dig('arguments', 'localfs') || req.dig('arguments', 'localfsMap')
         when 'attach'
           send_response req
           Process.kill(UI_ServerBase::TRAP_SIGNAL, Process.pid)
           @is_attach = true
-          UI_DAP.local_fs_set if req.dig('arguments', 'localfs')
+          UI_DAP.local_fs_map_set req.dig('arguments', 'localfs') || req.dig('arguments', 'localfsMap')
         when 'setBreakpoints'
           path = args.dig('source', 'path')
           SESSION.clear_line_breakpoints path
@@ -647,7 +672,9 @@ def process_dap args
           path = frame.realpath || frame.path
           source_name = path ? File.basename(path) : frame.location.to_s
 
-          if !UI_DAP.local_fs || !(path && File.exist?(path))
+          if (path && File.exist?(path)) && (local_path = UI_DAP.local_fs_map_path(path))
+            # ok
+          else
             ref = frame.file_lines
           end
 
@@ -658,7 +685,7 @@ def process_dap args
             column: 1,
             source: {
               name: source_name,
-              path: path,
+              path: (local_path || path),
               sourceReference: ref,
             },
           }