RFC: npm diff --diff-ignore-cr-at-eol

PR-URL: #522
Closes: #522

accepted/0044-npm-diff-ignore-cr-at-eol.md

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+# npm diff ignore CR at EOL
+
+## Summary
+
+An option to ignore Carriage Return (CR) at the end of lines when performing npm diff.
+
+## Motivation
+
+To improve `npm diff` on packages developed on different platforms. Currently 
+there are scenarios where every line is shown as changed if you are comparing
+to a package that was developed on a different platform than yours.
+
+## Detailed Explanation
+
+If you build a compiled package, e.g. with typescript `tsc` on windows, the 
+output is produced with CRLF (Carriage Return, Line Feed) line endings. 
+If you then build the same application on UNIX, the output is produced with
+LF line endings, as expected. 
+
+The problem arises when you want to see if your newly produced package has
+any changes compared to another package, if that package was produced
+on another platform.
+
+If the package you are comparing to is built on Windows, while you are
+working in UNIX, every produced file will be different because of the different
+file endings.
+
+This problem is avoided in some cases when the files you are comparing are
+tracked by git, depending on your git `autocrlf` configuration. The 
+scenarios where I've noticed this is when the files we are comparing are built
+locally and `.gitignore`d.
+
+I'm suggesting the flag `--diff-ignore-cr-at-eol`. This is quite a mouthful,
+but would be consistent with 
+[`git diff --ignore-cr-at-eol`](https://github.com/git/git/commit/e9282f02b2f21118f3383608718e38efc3d967e1)
+introduced in
+[`git v2.16`](https://git-scm.com/docs/git-diff/2.16.6). 
+
+## Rationale and Alternatives
+
+* Packages have their lineendings normalized when downloaded/installed from
+  the registry. 
+
+  Similiar to `git config core.autocrlf`, npm could also normalize line
+  endings when installing on a Windows machine. By doing this, 
+  `npm diff` would always be comparing files that are normalized for windows.
+
+  However this would be a big change with plenty of potential pitfall. It'd
+  also become problematic if a Windows user had configured git to keep files
+  with LF line endings and tried to compare to a package that npm would then
+  normalize to CRLF, again causing diffs...
+
+## Implementation
+
+A change to `libnpmdiff` to add a new option `diffIgnoreCRAtEOL` similiarly
+to the 
+[`diffIgnoreAllSpace` option](https://github.com/npm/cli/blob/892b66eba9f21dbfbc250572d437141e39a6de24/workspaces/libnpmdiff/lib/format-diff.js#L76). 
+However, as far as I can tell,
+[npmjs.com/diff](https://npmjs.com/diff)/[kpdecker/jsdiff](https://github.com/kpdecker/jsdiff/)
+does not have any option to do something like this. One option is to submit a
+PR to add this.
+
+Add the `--diff-ignore-cr-at-eol` configuration support to the npm cli and
+make sure `./lib/commands/diff.js` handles it as expected to `libnpmdiff`.
+
+## Prior Art
+
+* As mentioned previously 
+  [`git diff --ignore-cr-at-eol`](https://github.com/git/git/commit/e9282f02b2f21118f3383608718e38efc3d967e1)
+
+* Gnu diffutils 
+  [`diff --strip-trailing-cr`](https://www.gnu.org/software/diffutils/manual/html_node/diff-Options.html#diff-Options)