make use of termcolor crate to disable colors (#236)

* table: replace custom color by termcolor

* table: deactivate colors if not tty

* table: rename printable to print, add more comments

* table: make use of writters, fix tests

* doc: update changelog

* doc: add page to wiki

src/output/mod.rs

@@ -7,3 +7,6 @@ pub use output_utils::*;
 
 pub mod output_service;
 pub use output_service::*;
+
+pub mod print;
+pub use print::*;

src/output/output_service.rs

@@ -1,10 +1,14 @@
 use anyhow::{anyhow, Error, Result};
+use atty::Stream;
 use log::debug;
 use serde::Serialize;
 use std::{
     convert::{TryFrom, TryInto},
     fmt,
 };
+use termcolor::{ColorChoice, StandardStream};
+
+use crate::output::Print;
 
 #[derive(Debug, PartialEq)]
 pub enum OutputFmt {
@@ -58,7 +62,7 @@ impl<T: Serialize> OutputJson<T> {
 }
 
 pub trait OutputServiceInterface {
-    fn print<T: Serialize + fmt::Display>(&self, data: T) -> Result<()>;
+    fn print<T: Serialize + Print>(&self, data: T) -> Result<()>;
     fn is_json(&self) -> bool;
 }
 
@@ -70,10 +74,21 @@ pub struct OutputService {
 impl OutputServiceInterface for OutputService {
     /// Print the provided item out according to the formatting setting when you created this
     /// struct.
-    fn print<T: Serialize + fmt::Display>(&self, data: T) -> Result<()> {
+    fn print<T: Serialize + Print>(&self, data: T) -> Result<()> {
         match self.fmt {
             OutputFmt::Plain => {
-                println!("{}", data)
+                data.print(&mut StandardStream::stdout(if atty::isnt(Stream::Stdin) {
+                    // Colors should be deactivated if the terminal is not a tty.
+                    ColorChoice::Never
+                } else {
+                    // Otherwise let's `termcolor` decide by inspecting the environment. From the [doc]:
+                    // - If `NO_COLOR` is set to any value, then colors will be suppressed.
+                    // - If `TERM` is set to dumb, then colors will be suppressed.
+                    // - In non-Windows environments, if `TERM` is not set, then colors will be suppressed.
+                    //
+                    // [doc]: https://github.com/BurntSushi/termcolor#automatic-color-selection
+                    ColorChoice::Auto
+                }))?;
             }
             OutputFmt::Json => {
                 print!("{}", serde_json::to_string(&OutputJson::new(data))?)

src/output/print.rs

@@ -0,0 +1,28 @@
+use anyhow::{Context, Result};
+use std::io;
+use termcolor::{StandardStream, WriteColor};
+
+pub trait WriteWithColor: io::Write + WriteColor {}
+
+impl WriteWithColor for StandardStream {}
+
+pub trait Print {
+    fn print<W: WriteWithColor>(&self, writter: &mut W) -> Result<()>;
+
+    fn println<W: WriteWithColor>(&self, writter: &mut W) -> Result<()> {
+        println!();
+        self.print(writter)
+    }
+}
+
+impl Print for &str {
+    fn print<W: WriteWithColor>(&self, writter: &mut W) -> Result<()> {
+        write!(writter, "{}", self).context(format!(r#"cannot print string "{}""#, self))
+    }
+}
+
+impl Print for String {
+    fn print<W: WriteWithColor>(&self, writter: &mut W) -> Result<()> {
+        self.as_str().print(writter)
+    }
+}