merge review UI does not permit browsing of nearby source code

When reviewing a merge proposal, it's hard to see more context of the code if that is needed. Let me illustrate by example:

Reviewing some C code you often have to check that memory is being freed or properly initialized. Very often these sections are not visible in the diff. If I need to see the full scope of the code I must go to the branch's page, click "View branch content", and browse to the file in question. - And from that figure out where in the file the particular hunk of the diff applies.

This workflow is so cumbersome that people (including me) often end up not doing it, and resorting to second guessing.

What I'd like to see is some easy way to:

 1) Look at the code immediately surrounding a given hunk. Like +/- N lines for a suitably chosen N. Possibly highlighting in the expanded context where the diff applies

 2) See the entire file the hunk is applied to, and seeing in that file what the diff does. Or at the very least which lines are affected

Common use cases where this matters:

 A) Languages without memory management. C being the poster boy

 B) Languages without resource management (automatic closing of file handles etc)

 C) Code with lots of async interactions and callbacks where logic is not always very localised