Try to open stdio in non-blocking mode (#8787)

* Try to open stdio in non-blocking mode

* Some code style changes suggested by @Sija

spec/spec_helper.cr

@@ -256,7 +256,7 @@ def run(code, filename = nil, inject_primitives = true, debug = Crystal::Debug::
   end
 end
 
-def build_and_run(code)
+def build(code)
   code_file = File.tempname("build_and_run_code")
 
   # write code to the temp file
@@ -267,15 +267,21 @@ def build_and_run(code)
   `bin/crystal build #{encode_program_flags} #{code_file.path.inspect} -o #{binary_file.path.inspect}`
   File.exists?(binary_file).should be_true
 
-  out_io, err_io = IO::Memory.new, IO::Memory.new
-  status = Process.run(binary_file, output: out_io, error: err_io)
-
-  {status, out_io.to_s, err_io.to_s}
+  yield binary_file
 ensure
   File.delete(code_file) if code_file
   File.delete(binary_file) if binary_file
 end
 
+def build_and_run(code)
+  build(code) do |binary_file|
+    out_io, err_io = IO::Memory.new, IO::Memory.new
+    status = Process.run(binary_file, output: out_io, error: err_io)
+
+    {status, out_io.to_s, err_io.to_s}
+  end
+end
+
 def test_c(c_code, crystal_code)
   c_filename = "#{__DIR__}/temp_abi.c"
   o_filename = "#{__DIR__}/temp_abi.o"

spec/std/io/file_descriptor_spec.cr

@@ -0,0 +1,11 @@
+require "../../spec_helper"
+
+describe IO::FileDescriptor do
+  it "reopen STDIN with the right mode" do
+    code = %q(puts "#{STDIN.blocking} #{STDIN.info.type}")
+    build(code) do |binpath|
+      `#{binpath} < #{binpath}`.chomp.should eq("true File")
+      `echo "" | #{binpath}`.chomp.should eq("false Pipe")
+    end
+  end
+end

src/io/file_descriptor.cr

@@ -9,9 +9,19 @@ class IO::FileDescriptor < IO
   # platform-specific.
   getter fd
 
-  def initialize(@fd, blocking = false)
+  def initialize(@fd, blocking = nil)
     @closed = system_closed?
 
+    if blocking.nil?
+      blocking =
+        case system_info.type
+        when .pipe?, .socket?, .character_device?
+          false
+        else
+          true
+        end
+    end
+
     unless blocking || {{flag?(:win32)}}
       self.blocking = false
     end
@@ -25,10 +35,10 @@ class IO::FileDescriptor < IO
     # Figure out the terminal TTY name. If ttyname fails we have a non-tty, or something strange.
     path = uninitialized UInt8[256]
     ret = LibC.ttyname_r(fd, path, 256)
-    return new(fd, blocking: true) unless ret == 0
+    return new(fd) unless ret == 0
 
     clone_fd = LibC.open(path, LibC::O_RDWR)
-    return new(fd, blocking: true) if clone_fd == -1
+    return new(fd) if clone_fd == -1
 
     # We don't buffer output for TTY devices to see their output right away
     io = new(clone_fd)