Add flag to configure large_assignments lint

[tmiasko]

The large_assignments lints detects moves over specified limit. The
limit is configured through move_size_limit = "N" attribute placed at
the root of a crate. When attribute is absent, the lint is disabled.

Make it possible to enable the lint without making any changes to the
source code, through a new flag -Zmove-size-limit=N. For example, to
detect moves exceeding 1023 bytes in a cargo crate, including all
dependencies one could use:

$ env RUSTFLAGS=-Zmove-size-limit=1024 cargo build -vv

Lint tracking issue #83518.

[rust-highfive]

r? @LeSeulArtichaut

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[tmiasko]

A few examples

warning: moving 16384 bytes
  --> ~/.cargo/registry/src/github.heygears.com-1ecc6299db9ec823/crc32fast-1.2.1/src/baseline.rs:38:19
   |
38 |             crc = CRC32_TABLE[0x0][buf[0xf] as usize]
   |                   ^^^^^^^^^^^ value moved from here
   |

warning: moving 16384 bytes
  --> ~/.cargo/registry/src/github.heygears.com-1ecc6299db9ec823/crc32fast-1.2.1/src/baseline.rs:39:19
   |
39 |                 ^ CRC32_TABLE[0x1][buf[0xe] as usize]
   |                   ^^^^^^^^^^^ value moved from here

...

warning: moving 65536 bytes
  --> ~/.cargo/registry/src/github.heygears.com-1ecc6299db9ec823/h2-0.3.3/src/hpack/huffman/mod.rs:92:35
   |
92 |         let (next, byte, flags) = DECODE_TABLE[self.state][input as usize];
   |                                   ^^^^^^^^^^^^ value moved from here
   |
   = note: `#[warn(large_assignments)]` on by default

warning: moving 4112 bytes
  --> ~/.cargo/registry/src/github.heygears.com-1ecc6299db9ec823/h2-0.3.3/src/hpack/huffman/mod.rs:50:29
   |
50 |         let (nbits, code) = ENCODE_TABLE[b as usize];
   |                             ^^^^^^^^^^^^ value moved from here

We should probably lint large consts by default.

cc @oli-obk

[oli-obk]

r? @pnkfelix

[bors]

☔ The latest upstream changes (presumably #86674) made this pull request unmergeable. Please resolve the merge conflicts.

[tmiasko]

• Rebased and resolved conflicts with Query-ify global limit attribute handling #86674.
• Added a new entry to the unstable book describing the new flag.

[pnkfelix]

@bors r+ rollup

[bors]

📌 Commit 9792179 has been approved by pnkfelix