large_stack_frames: print total size and largest component.

[kpreid]

Instead of just saying “this function's stack frame is big”, report:

• the (presumed) size of the frame
• the size and type of the largest local contributing to that size
• the configurable limit that was exceeded (once)

Known issues:

• The lint may report an over-estimate because codegen may be able to overlap some of these locals. However, that already affected whether the lint fired at all; I believe this change is still an improvement because it gives the user much more actionable information about why the lint fired.
• Please tell me a better way to determine whether a local has a variable name.

changelog: [large_stack_frames]: print total size and largest component.

[rustbot]

r? @Manishearth

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[Manishearth]

praise: good idea

[Manishearth]

@bors r+

[bors]

📌 Commit 0164645 has been approved by Manishearth

It is now in the queue for this repository.

[bors]

⌛ Testing commit 0164645 with merge 97ba291...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Manishearth
Pushing 97ba291 to master...