Add long error code explanation message for E0203

[aDotInTheVoid]

Addressed some of #61137

r? @GuillaumeGomez

[rust-highfive]

Some changes occurred in diagnostic error codes

cc @GuillaumeGomez

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @GuillaumeGomez (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

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[GuillaumeGomez]

Looks good globally. Just a few little things missing. Can you extend your explanation of the error a bit more and also add a working example (the failing code fixed) please? Once done, I'll review one last time and then I think it'll be good to go!

[GuillaumeGomez]

Sorry, closed by mistake...

[rust-highfive]

The job x86_64-gnu-llvm-6.0 of your PR failed (pretty log, raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

2019-11-30T10:56:54.9680115Z ##[command]git remote add origin https://github.com/rust-lang/rust
2019-11-30T10:56:55.9342142Z ##[command]git config gc.auto 0
2019-11-30T10:56:55.9344748Z ##[command]git config --get-all http.https://github.com/rust-lang/rust.extraheader
2019-11-30T10:56:55.9346718Z ##[command]git config --get-all http.proxy
2019-11-30T10:56:55.9351654Z ##[command]git -c http.extraheader="AUTHORIZATION: basic ***" fetch --force --tags --prune --progress --no-recurse-submodules --depth=2 origin +refs/heads/*:refs/remotes/origin/* +refs/pull/66880/merge:refs/remotes/pull/66880/merge
---
2019-11-30T11:02:10.3568685Z    Compiling serde_json v1.0.40
2019-11-30T11:02:11.7759313Z    Compiling tidy v0.1.0 (/checkout/src/tools/tidy)
2019-11-30T11:02:20.6927296Z     Finished release [optimized] target(s) in 1m 10s
2019-11-30T11:02:20.7012258Z tidy check
2019-11-30T11:02:21.2874252Z tidy error: /checkout/src/librustc_error_codes/error_codes/E0203.md: missing trailing newline
2019-11-30T11:02:22.7925011Z Found 486 error codes
2019-11-30T11:02:22.7925935Z Found 0 error codes with no tests
2019-11-30T11:02:22.7926047Z Done!
2019-11-30T11:02:22.7926295Z some tidy checks failed
2019-11-30T11:02:22.7926295Z some tidy checks failed
2019-11-30T11:02:22.7929217Z 
2019-11-30T11:02:22.7929458Z 
2019-11-30T11:02:22.7930404Z command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor"
2019-11-30T11:02:22.7930563Z 
2019-11-30T11:02:22.7930583Z 
2019-11-30T11:02:22.7938087Z failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
2019-11-30T11:02:22.7938187Z Build completed unsuccessfully in 0:01:14
2019-11-30T11:02:22.7938187Z Build completed unsuccessfully in 0:01:14
2019-11-30T11:02:22.7976817Z == clock drift check ==
2019-11-30T11:02:22.7986537Z   local time: Sat Nov 30 11:02:22 UTC 2019
2019-11-30T11:02:22.9469668Z   network time: Sat, 30 Nov 2019 11:02:22 GMT
2019-11-30T11:02:22.9470177Z == end clock drift check ==
2019-11-30T11:02:24.3313658Z 
2019-11-30T11:02:24.3393112Z ##[error]Bash exited with code '1'.
2019-11-30T11:02:24.3419363Z ##[section]Starting: Checkout
2019-11-30T11:02:24.3420693Z ==============================================================================
2019-11-30T11:02:24.3420734Z Task         : Get sources
2019-11-30T11:02:24.3420904Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[GuillaumeGomez]

Thanks!

@bors: r+ rollup

[bors]

📌 Commit a52eb05 has been approved by GuillaumeGomez

[bors]

🌲 The tree is currently closed for pull requests below priority 1000, this pull request will be tested once the tree is reopened