1 files changed, 171 insertions, 0 deletions
diff --git a/cli/diff.rs b/cli/diff.rs
new file mode 100644
index 000000000..e6d7fa4bb
--- /dev/null
+++ b/cli/diff.rs
@@ -0,0 +1,171 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+use crate::colors;
+use dissimilar::{diff as difference, Chunk};
+use std::fmt;
+use std::fmt::Write;
+
+fn fmt_add() -> String {
+  format!("{}", colors::green_bold("+".to_string()))
+}
+
+fn fmt_add_text(x: String) -> String {
+  format!("{}", colors::green(x))
+}
+
+fn fmt_add_text_highlight(x: String) -> String {
+  format!("{}", colors::white_on_green(x))
+}
+
+fn fmt_rem() -> String {
+  format!("{}", colors::red_bold("-".to_string()))
+}
+
+fn fmt_rem_text(x: String) -> String {
+  format!("{}", colors::red(x))
+}
+
+fn fmt_rem_text_highlight(x: String) -> String {
+  format!("{}", colors::white_on_red(x))
+}
+
+fn write_line_diff(
+  diff: &mut String,
+  orig_line: &mut usize,
+  edit_line: &mut usize,
+  line_number_width: usize,
+  orig: &mut String,
+  edit: &mut String,
+) -> fmt::Result {
+  let split = orig.split('\n').enumerate();
+  for (i, s) in split {
+    write!(
+      diff,
+      "{:0width$}{} ",
+      *orig_line + i,
+      colors::gray("|".to_string()),
+      width = line_number_width
+    )?;
+    write!(diff, "{}", fmt_rem())?;
+    write!(diff, "{}", s)?;
+    writeln!(diff)?;
+  }
+
+  let split = edit.split('\n').enumerate();
+  for (i, s) in split {
+    write!(
+      diff,
+      "{:0width$}{} ",
+      *edit_line + i,
+      colors::gray("|".to_string()),
+      width = line_number_width
+    )?;
+    write!(diff, "{}", fmt_add())?;
+    write!(diff, "{}", s)?;
+    writeln!(diff)?;
+  }
+
+  *orig_line += orig.split('\n').count();
+  *edit_line += edit.split('\n').count();
+
+  orig.clear();
+  edit.clear();
+
+  Ok(())
+}
+
+/// Print diff of the same file_path, before and after formatting.
+///
+/// Diff format is loosely based on Github diff formatting.
+pub fn diff(orig_text: &str, edit_text: &str) -> Result<String, fmt::Error> {
+  let lines = edit_text.split('\n').count();
+  let line_number_width = lines.to_string().chars().count();
+
+  let mut diff = String::new();
+
+  let mut text1 = orig_text.to_string();
+  let mut text2 = edit_text.to_string();
+
+  if !text1.ends_with('\n') {
+    writeln!(text1)?;
+  }
+  if !text2.ends_with('\n') {
+    writeln!(text2)?;
+  }
+
+  let mut orig_line: usize = 1;
+  let mut edit_line: usize = 1;
+  let mut orig: String = String::new();
+  let mut edit: String = String::new();
+  let mut changes = false;
+
+  let chunks = difference(&text1, &text2);
+  for chunk in chunks {
+    match chunk {
+      Chunk::Delete(s) => {
+        let split = s.split('\n').enumerate();
+        for (i, s) in split {
+          if i > 0 {
+            orig.push_str("\n");
+          }
+          orig.push_str(&fmt_rem_text_highlight(s.to_string()));
+        }
+        changes = true
+      }
+      Chunk::Insert(s) => {
+        let split = s.split('\n').enumerate();
+        for (i, s) in split {
+          if i > 0 {
+            edit.push_str("\n");
+          }
+          edit.push_str(&fmt_add_text_highlight(s.to_string()));
+        }
+        changes = true
+      }
+      Chunk::Equal(s) => {
+        let split = s.split('\n').enumerate();
+        for (i, s) in split {
+          if i > 0 {
+            if changes {
+              write_line_diff(
+                &mut diff,
+                &mut orig_line,
+                &mut edit_line,
+                line_number_width,
+                &mut orig,
+                &mut edit,
+              )?;
+              changes = false
+            } else {
+              orig.clear();
+              edit.clear();
+              orig_line += 1;
+              edit_line += 1;
+            }
+          }
+          orig.push_str(&fmt_rem_text(s.to_string()));
+          edit.push_str(&fmt_add_text(s.to_string()));
+        }
+      }
+    }
+  }
+  Ok(diff)
+}
+
+#[test]
+fn test_diff() {
+  let simple_console_log_unfmt = "console.log('Hello World')";
+  let simple_console_log_fmt = "console.log(\"Hello World\");";
+  assert_eq!(
+    colors::strip_ansi_codes(
+      &diff(simple_console_log_unfmt, simple_console_log_fmt).unwrap()
+    ),
+    "1| -console.log('Hello World')\n1| +console.log(\"Hello World\");\n"
+  );
+
+  let line_number_unfmt = "\n\n\n\nconsole.log(\n'Hello World'\n)";
+  let line_number_fmt = "console.log(\n\"Hello World\"\n);";
+  assert_eq!(
+    colors::strip_ansi_codes(&diff(line_number_unfmt, line_number_fmt).unwrap()),
+    "1| -\n2| -\n3| -\n4| -\n5| -console.log(\n1| +console.log(\n6| -'Hello World'\n2| +\"Hello World\"\n7| -)\n3| +);\n"
+  )
+}