Add map unwrap or lint for Result

[guanqun]

with the introduction of map_or() in Result by @lzutao , we should add the similar lint.

---

changelog: none

[guanqun]

hmm. why following errors? I can build locally.

error[E0063]: missing field `force_run_in_process` in initializer of `test::TestOpts`

   --> /home/travis/.cargo/registry/src/github.com-1ecc6299db9ec823/compiletest_rs-0.3.25/src/lib.rs:110:5

    |

110 |     test::TestOpts {

    |     ^^^^^^^^^^^^^^ missing `force_run_in_process`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0063`.

[JohnTitor]

clippy build with the latest master is currently broken, it's not your fault.

[flip1995]

This is blocked on the stabilization of Result::map_or

[jfrimmel]

cc rust-lang/rust#66570

[bors]

☔ The latest upstream changes (presumably #4839) made this pull request unmergeable. Please resolve the merge conflicts.

[tesuji]

rust-lang/rust#66570 merged. This could be continued.

[guanqun]

Thank you @lzutao for the headsup, will work on the conflicts.

[guanqun]

conflicts resolved, could you please help review again?

[guanqun]

@lzutao could you please help review again? Thanks!

[bors]

☔ The latest upstream changes (presumably #4930) made this pull request unmergeable. Please resolve the merge conflicts.

[flip1995]

Sorry for the late reply, I was on vacation. The formatting of the lint message, note and help can still be improved.

[flip1995]

Can you do this by using the function

span_lint_and_then(
    ..,
    |db| {
         db.note("this can be done more directly by calling `map_or(a, f)` instead");
         if multiline {
               db.span_help(.., format!("replace `map({}).unwrap_or({})` with `{}`", ..);
         }
    },
);

[bors]

☔ The latest upstream changes (presumably #4962) made this pull request unmergeable. Please resolve the merge conflicts.

[tesuji]

Can we suggest with Result::ok().map_or case too?

[flip1995]

Thanks for contributing to Clippy! Sadly this PR was not updated in quite some time. If you waited on input from a reviewer, we're sorry that this fell under the radar. If you want to continue to work on this, just reopen the PR and/or ping a reviewer.