Added basic assertion example

Cargo.toml

@@ -33,6 +33,10 @@ console = "0.14.0"
 unicode-segmentation = { version = "1.7.1", optional = true }
 bstr = { version = "0.2.14", optional = true, default-features = false }
 
+[[example]]
+name = "assert"
+required-features = ["text", "inline"]
+
 [[example]]
 name = "terminal"
 required-features = ["text"]

examples/assert.rs

@@ -0,0 +1,126 @@
+use std::fmt;
+
+use console::{style, Style};
+use similar::{Algorithm, ChangeTag, TextDiff};
+
+pub struct Diff {
+    left: String,
+    right: String,
+}
+
+fn to_debug<D: fmt::Debug>(d: &D) -> String {
+    use fmt::Write;
+    let mut buf = String::new();
+    buf.write_fmt(format_args!("{:#?}", d))
+        .expect("a Debug implementation returned an error unexpectedly");
+    buf
+}
+
+impl Diff {
+    pub fn from_debug<Left: fmt::Debug, Right: fmt::Debug>(left: &Left, right: &Right) -> Diff {
+        let left = to_debug(left).into();
+        let right = to_debug(right).into();
+        Diff { left, right }
+    }
+}
+
+impl fmt::Display for Diff {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.left == self.right {
+            writeln!(
+                f,
+                "{}: {}",
+                style("Invisible differences").bold(),
+                "the two values are the same in string form."
+            )?;
+            return Ok(());
+        }
+
+        let diff = TextDiff::configure()
+            .algorithm(Algorithm::Patience)
+            .diff_lines(&self.left, &self.right);
+        writeln!(
+            f,
+            "  {} ({}|{}):",
+            style("Differences").bold(),
+            style("<left").red(),
+            style(">right").green(),
+        )?;
+        for (idx, group) in diff.grouped_ops(4).into_iter().enumerate() {
+            if idx > 0 {
+                writeln!(f, "  ~~~")?;
+            }
+            for op in group {
+                for change in diff.iter_inline_changes(&op) {
+                    let (marker, style) = match change.tag() {
+                        ChangeTag::Delete => ('<', Style::new().red()),
+                        ChangeTag::Insert => ('>', Style::new().green()),
+                        ChangeTag::Equal => (' ', Style::new().dim()),
+                    };
+                    write!(f, "   {}", style.apply_to(marker).dim().bold())?;
+                    #[cfg(feature = "inline")]
+                    {
+                        for &(emphasized, value) in change.values() {
+                            if emphasized {
+                                write!(f, "{}", style.clone().underlined().bold().apply_to(value))?;
+                            } else {
+                                write!(f, "{}", style.apply_to(value))?;
+                            }
+                        }
+                    }
+                    #[cfg(not(feature = "inline"))]
+                    {
+                        write!(f, "{}", style.apply_to(change.value()))?;
+                    }
+                    if change.missing_newline() {
+                        writeln!(f)?;
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+}
+
+#[macro_export]
+macro_rules! assert_eq {
+    ($left:expr, $right:expr $(,)?) => ({
+        match (&($left), &($right)) {
+            (left_val, right_val) => {
+                if !(*left_val == *right_val) {
+                    panic!("assertion failed: `(left == right)`'\
+                           \n  left: `{:?}`\
+                           \n right: `{:?}`\
+                           \n\n{}\n",
+                           &*left_val,
+                           &*right_val,
+                           $crate::Diff::from_debug(&*left_val, &*right_val));
+                }
+            }
+        }
+    });
+    ($left:expr, $right:expr, $($arg:tt)*) => ({
+        match (&($left), &($right)) {
+            (left_val, right_val) => {
+                if !(*left_val == *right_val) {
+                    panic!("assertion failed: `(left == right)`: {}'\
+                           \n  left: `{:?}`\
+                           \n right: `{:?}`\
+                           \n\n{}\n",
+                           format_args!($($arg)*),
+                           &*left_val,
+                           &*right_val,
+                           $crate::Diff::from_debug(&*left_val, &*right_val));
+                }
+            }
+        }
+    });
+}
+
+fn main() {
+    let vec1: Vec<_> = (1..100).collect();
+    let mut vec2 = vec1.clone();
+    vec2[52] = 2;
+    vec2[12] = 33;
+    assert_eq!(vec1, vec2);
+}