Merge pull request de-vri-es#28 from TheFurnace/issue/27/proposal

Collect output to buffer then print to stdErr once

src/__assert2_impl/print.rs

@@ -1,6 +1,7 @@
 use atty::Stream;
 use std::fmt::Debug;
 use yansi::Paint;
+use std::fmt::Write;
 
 fn should_color() -> bool {
 	if std::env::var_os("CLICOLOR").map(|x| x == "0").unwrap_or(false) {
@@ -31,8 +32,8 @@ pub struct FailedCheck<'a, T> {
 }
 
 pub trait CheckExpression {
-	fn print_expression(&self);
-	fn print_expansion(&self);
+	fn print_expression(&self, print_message: &mut  String);
+	fn print_expansion(&self, print_message: &mut String);
 }
 
 pub struct BinaryOp<'a, Left, Right> {
@@ -58,77 +59,80 @@ impl<'a, T: CheckExpression> FailedCheck<'a, T> {
 	#[rustfmt::skip]
 	pub fn print(&self) {
 		set_color();
-		eprintln!("{msg} at {file}:{line}:{column}:",
+		let mut print_message = String::new();
+		writeln!(&mut print_message, "{msg} at {file}:{line}:{column}:",
 			msg    = Paint::red("Assertion failed").bold(),
 			file   = Paint::default(self.file).bold(),
 			line   = self.line,
 			column = self.column,
-		);
-		eprint!("  {name}{open} ",
+		).unwrap();
+		write!(&mut print_message, "  {name}{open} ",
 			name = Paint::magenta(self.macro_name),
 			open = Paint::magenta("!("),
-		);
-		self.expression.print_expression();
-		eprintln!(" {}", Paint::magenta(")"));
+		).unwrap();
+		self.expression.print_expression(&mut print_message);
+		writeln!(&mut print_message, " {}", Paint::magenta(")")).unwrap();
 		if !self.fragments.is_empty() {
-			eprintln!("with:");
+			writeln!(&mut print_message, "with:").unwrap();
 			for (name, expansion) in self.fragments {
-				eprintln!("  {} {} {}", Paint::magenta(name), Paint::blue("=").bold(), expansion);
+				writeln!(&mut print_message, "  {} {} {}", Paint::magenta(name), Paint::blue("=").bold(), expansion).unwrap();
 			}
 		}
-		eprintln!("with expansion:");
-		eprint!("  ");
-		self.expression.print_expansion();
-		eprintln!();
+		writeln!(&mut print_message, "with expansion:").unwrap();
+		write!(&mut print_message, "  ").unwrap();
+		self.expression.print_expansion(&mut print_message);
+		writeln!(&mut print_message, ).unwrap();
 		if let Some(msg) = self.custom_msg {
-			eprintln!("with message:");
-			eprintln!("  {}", Paint::default(msg).bold());
+			writeln!(&mut print_message, "with message:").unwrap();
+			writeln!(&mut print_message, "  {}", Paint::default(msg).bold()).unwrap();
 		}
-		eprintln!();
+		writeln!(&mut print_message).unwrap();
+
+		eprint!("{}", print_message);
 	}
 }
 
 #[rustfmt::skip]
 impl<Left: Debug, Right: Debug> CheckExpression for BinaryOp<'_, Left, Right> {
-	fn print_expression(&self) {
-		eprint!("{left} {op} {right}",
+	fn print_expression(&self, print_message: &mut  String) {
+		write!(print_message, "{left} {op} {right}",
 			left  = Paint::cyan(self.left_expr),
 			op    = Paint::blue(self.operator).bold(),
 			right = Paint::yellow(self.right_expr),
-		);
+		).unwrap();
 	}
-	fn print_expansion(&self) {
-		eprint!("{left:?} {op} {right:?}",
+	fn print_expansion(&self, print_message: &mut  String) {
+		write!(print_message, "{left:?} {op} {right:?}",
 			left  = Paint::cyan(self.left),
 			op    = Paint::blue(self.operator).bold(),
 			right = Paint::yellow(self.right),
-		);
+		).unwrap();
 	}
 }
 
 #[rustfmt::skip]
 impl CheckExpression for BooleanExpr<'_> {
-	fn print_expression(&self) {
-		eprint!("{}", Paint::cyan(self.expression));
+	fn print_expression(&self, print_message: &mut  String) {
+		write!(print_message, "{}", Paint::cyan(self.expression)).unwrap();
 	}
-	fn print_expansion(&self) {
-		eprint!("{:?}", Paint::cyan(false));
+	fn print_expansion(&self, print_message: &mut String) {
+		write!(print_message, "{:?}", Paint::cyan(false)).unwrap();
 	}
 }
 
 #[rustfmt::skip]
 impl<Value: Debug> CheckExpression for MatchExpr<'_, Value> {
-	fn print_expression(&self) {
+	fn print_expression(&self, print_message: &mut String) {
 		if self.print_let {
-			eprint!("{} ", Paint::blue("let").bold());
+			write!(print_message, "{} ", Paint::blue("let").bold()).unwrap();
 		}
-		eprint!("{pat} {eq} {expr}",
+		write!(print_message, "{pat} {eq} {expr}",
 			pat  = Paint::cyan(self.pattern),
 			eq   = Paint::blue("=").bold(),
 			expr = Paint::yellow(self.expression),
-		);
+		).unwrap();
 	}
-	fn print_expansion(&self) {
-		eprint!("{:?}", Paint::yellow(self.value));
+	fn print_expansion(&self, print_message: &mut String) {
+		write!(print_message, "{:?}", Paint::yellow(self.value)).unwrap();
 	}
 }