sarutak opened a new pull request #33599:
URL: https://github.com/apache/spark/pull/33599


   ### What changes were proposed in this pull request?
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   This PR proposes to support raw string literal which escape no character 
using `\`.
   The raw string literal is the form of `r"..."` or `r'...'` like the syntax 
Python supports.
   
   ### Why are the changes needed?
   <!--
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     1. If you propose a new API, clarify the use case for a new API.
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   In the current master, sometimes it's too confusable to represent JSON and 
regex in a string literal if they contain backslash.
   For example, in JSON, `\` needs to be escaped like as follows.
   ```
   {"a": "\\"}
   ```
   But, if the JSON above is represented in a string literal, further two `\` 
are needed because string literal also requires `\` to be escaped.
   ```
   SELECT from_json('{"a": "\\\\"}', 'a string')
   {"a":"\"}
   ```
   With the raw string literal, we can represent such JSON like as follows.
   ```
   SELECT from_json(r'{"a": "\\"}', 'a string')
   {"a":"\"}
   ```
   
   ### Does this PR introduce _any_ user-facing change?
   <!--
   Note that it means *any* user-facing change including all aspects such as 
the documentation fix.
   If yes, please clarify the previous behavior and the change this PR proposes 
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   No. This PR just extends the existing syntax.
   
   ### How was this patch tested?
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it was difficult to add.
   -->
   Added new test.
   I also confirmed that the modified document is successfully built with 
`SKIP_API=1 bundle exec jekyll build`.
   
![raw_literal](https://user-images.githubusercontent.com/4736016/127746410-eb3fc001-f056-47b8-93e5-9d48ba065817.png)
   


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