[stdlib,spec] Add basic specs for File, temporary workaround for `I…

…O#gets` issue.

The explicit return in `IO#gets` caused issues with the value of `self` (see myst-lang#155), so `raise/rescue` is used as a temporary workaround.

Also, the specs for File are a bit light, because there currently isn't a great way of mocking FileDescriptor input, nor accessing the Interpreter's `fd_pool` to check for opening/closing of files.

spec/myst/file_spec.mt

@@ -0,0 +1,28 @@
+require "stdlib/spec.mt"
+
+
+describe("File#open") do
+  it("returns a new File instance for the given file") do
+    file = File.open("spec/support/misc/fixed_size_file.txt", "r")
+
+    assert(file.type.to_s == "File")
+  end
+
+  it("defaults to 'read' mode if no mode is given") do
+    file = File.open("spec/support/misc/fixed_size_file.txt")
+    assert(file.mode == "r")
+  end
+end
+
+describe("File#close") do
+  # TODO: test that the file descriptor is properly closed.
+end
+
+describe("File#size") do
+  it("returns an Integer of the number of bytes the file contains") do
+    # `fixed_size_file.txt` should always be 63 bytes in size.
+    file = %File{"spec/support/misc/fixed_size_file.txt", "r"}
+
+    assert(file.size == 63)
+  end
+end

spec/myst/spec.mt

@@ -7,6 +7,7 @@ include Spec.DSL
 # files under this directory.
 require "./boolean_spec.mt"
 require "./enumerable_spec.mt"
+require "./file_spec.mt"
 require "./float_spec.mt"
 require "./integer_spec.mt"
 require "./io_spec.mt"

spec/support/misc/fixed_size_file.txt

@@ -0,0 +1 @@
+This file has a fixed size of 63 bytes. Do not edit this file!

src/myst/interpreter/native_lib/file.cr

@@ -4,25 +4,33 @@ module Myst
       file = File.open(name.value, mode.value)
       @fd_pool[file.fd] = file
 
-      this.ivars["fd"] = TInteger.new(file.fd.to_i64)
+      this.ivars["@fd"] = TInteger.new(file.fd.to_i64)
+      this.ivars["@mode"] = mode
       this
     end
 
     NativeLib.method :file_close, TInstance do
-      fd = this.ivars["fd"].as(TInteger)
+      fd = this.ivars["@fd"].as(TInteger)
       file = @fd_pool[fd.value]
       file.close
       @fd_pool.delete(fd.value)
       TNil.new
     end
 
+    NativeLib.method :file_size, TInstance do
+      fd = this.ivars["@fd"].as(TInteger)
+      file = @fd_pool[fd.value].as(File)
+      TInteger.new(file.size.to_i64)
+    end
+
 
     def init_file(kernel : TModule, fd_type : TType)
       file_type = TType.new("File", kernel.scope, fd_type)
       kernel.scope["File"] = file_type
 
       NativeLib.def_instance_method(file_type, :initialize, :file_init)
       NativeLib.def_instance_method(file_type, :close,      :file_close)
+      NativeLib.def_instance_method(file_type, :size,       :file_size)
       file_type
     end
   end

stdlib/file.mt

@@ -5,4 +5,6 @@ deftype File
   defstatic open(name : String, mode)
     %File{name, mode}
   end
+
+  def mode; @mode; end
 end

stdlib/io.mt

@@ -39,14 +39,20 @@ deftype IO
   def gets
     buffer = ""
     last_char = ""
+
     while last_char != "\n"
       buffer += last_char
       last_char = read(1)
 
       when last_char == "" || last_char == "\0"
-        return buffer
+        # raise/rescue is a work around for the currently-broken explicit
+        # returns, mentioned in https://github.com/myst-lang/myst/issues/155.
+        raise buffer
       end
     end
+
+    buffer
+  rescue buffer
     buffer
   end
 end