Better support for info strings in fenced code blocks containing more than just the language

[fasiha]

Prerequisites

• [X] Put an X between the brackets on this line if you have done all of the following:
  • Reproduced the problem in Safe Mode: http://flight-manual.atom.io/hacking-atom/sections/debugging/#using-safe-mode
  • Followed all applicable steps in the debugging guide: http://flight-manual.atom.io/hacking-atom/sections/debugging/
  • Checked the FAQs on the message board for common solutions: https://discuss.atom.io/c/faq
  • Checked that your issue isn't already filed: https://github.com/issues?utf8=✓&q=is%3Aissue+user%3Aatom
  • Checked that there is not already an Atom package that provides the described functionality: https://atom.io/packages

Better support for info strings in fenced code blocks containing more than just the language

If I start a fenced code block, and add an info string like py, the fenced code block will be highlighted as Python. So far so good. But if I make it py base.py, e.g., Atom stops formatting the code block as Python because language-gfm parses the entire info string, including trailing characters, as the language name (a guess).

Consider interpreting the info string’s text only up to the the first whitespace/punctuation as the language specifier?

Steps to Reproduce

1. Create a fenced code block with ticks.
2. Add a language specification to after the opening triplet and confirm that the code is highlighted as that language
3. Add a space and some more text.

Expected behavior: The code block retains the syntax highlighting

Actual behavior: The code block is shown as a plain codeblock as if it lacked an info string

Reproduces how often: 100%

Versions

Atom:

Atom    : 1.16.0
Electron: 1.3.13
Chrome  : 52.0.2743.82
Node    : 6.5.0

apm:

apm  1.16.1
npm  3.10.5
node 6.9.5 x64
python 2.7.13
git 2.9.2

macOS Sierra.

[kachkaev]

Same here in Atom 1.26.0 on macOS, even in Safe Mode.

source

Example code listing

````markdown
# fenced code block without arguments
```js
const x = 42; // highlighting works
```

# fenced code block with arguments
```js {something=something}
const x = 42; // no highlighting here
```
````

Looks like the same code is used to highlight stuff on Github. Check out these examples:

```js
const x = 42;

↓
```js
const x = 42;

ok

---

```js {something=something}
const x = 42;

↓
```js {something=something}
const x = 42;

ok

---

````markdown
# fenced code block without arguments
```js
const x = 42;

fenced code block with arguments

const x = 42;

↓

# fenced code block without arguments
```js
const x = 42;

fenced code block with arguments

const x = 42;

_highlighting inside ` ```js {something=something}` does not happen_

If I manage to fix this, would the change propagate to GitHub.com? I'd like to get online highlighting working [in this README](https://github.com/gicentre/litvis/blob/2ba014df51700010cc52f5626f85ac78842cfc7f/documents/README.md).