Add no-modifier-without-element-usage rule

[NullVoxPopuli]

New rule: report a modifier that never references its element.

A modifier that ignores its element is an effect scheduled by render, which is the data flow no-at-ember-render-modifiers exists to remove. That rule only bans an import, so the same pattern is reachable with three lines of ember-modifier.

Both styles are checked:

Style	Element source
modifier(fn) from ember-modifier	first param of the callback
class extending the default export or ClassBasedModifier	first param of modify(), or this.element anywhere in the class

Any reference counts as usage, including destructuring and passing the element to something else. A missing first param is a violation. modify = someHelper is skipped, since the function is not visible here.

Not added to recommended. That is proposed for v14 in emberjs/rfcs#1217.

🤖 Generated with Claude Code

[github-actions]

🏎️ Benchmark Comparison

	Benchmark	Control (p50)	Experiment (p50)	Δ
⚪	js small	14.27 ms	14.20 ms	-0.5%
🟢	js medium	7.11 ms	6.96 ms	-2.1%
🟢	js large	2.81 ms	2.72 ms	-3.3%
⚪	gjs small	1.12 ms	1.12 ms	+0.1%
⚪	gjs medium	557.57 µs	558.48 µs	+0.2%
⚪	gjs large	221.67 µs	219.22 µs	-1.1%
⚪	gts small	1.11 ms	1.11 ms	+0.0%
⚪	gts medium	555.31 µs	552.68 µs	-0.5%
⚪	gts large	219.71 µs	220.17 µs	+0.2%

🟢 faster · 🔴 slower · 🟠 slightly slower · ⚪ within 2%

Full mitata output

clk: ~2.70 GHz
cpu: AMD EPYC 9V74 80-Core Processor
runtime: node 24.19.0 (x64-linux)

benchmark                   avg (min … max) p75 / p99    (min … top 1%)
------------------------------------------- -------------------------------
js small (control)            17.50 ms/iter  18.47 ms █                    
                      (12.27 ms … 34.28 ms)  32.39 ms █ █                  
                    (  5.41 mb …  10.53 mb)   7.38 mb █▆█▃▆▃█▁▃▁▃▁▃▃▁▆▁▃▁▁▃

js small (experiment)         15.87 ms/iter  16.40 ms  █                   
                      (12.89 ms … 23.84 ms)  23.72 ms  █▂ ▂                
                    (  6.18 mb …   8.36 mb)   6.89 mb ▅██▁█▆▃▃▃▁▃▁▁▃▁▃▃▁▁▃▅

                             ┌                                            ┐
                             ╷┌──────────┬─┐                              ╷
          js small (control) ├┤          │ ├──────────────────────────────┤
                             ╵└──────────┴─┘                              ╵
                              ╷ ┌────┬┐                ╷
       js small (experiment)  ├─┤    │├────────────────┤
                              ╵ └────┴┘                ╵
                             └                                            ┘
                             12.27 ms           22.33 ms           32.39 ms

summary
  js small (experiment)
   1.1x faster than js small (control)

------------------------------------------- -------------------------------
js medium (control)            7.94 ms/iter   8.37 ms ▃█                   
                       (6.64 ms … 16.11 ms)  15.74 ms ██                   
                    (  2.70 mb …   5.01 mb)   3.58 mb ██▇▄▅▄▄▂▂▁▁▄▂▁▁▂▁▁▁▁▂

js medium (experiment)         7.60 ms/iter   8.10 ms ▂█                   
                       (6.41 ms … 14.25 ms)  13.18 ms ███                  
                    (  1.87 mb …   5.16 mb)   3.57 mb ███▇▄▆▆▄▂▂▂▂▁▁▄▁▁▁▂▁▂

                             ┌                                            ┐
                              ╷┌────┬─┐                                   ╷
         js medium (control)  ├┤    │ ├───────────────────────────────────┤
                              ╵└────┴─┘                                   ╵
                             ╷┌────┬─┐                        ╷
      js medium (experiment) ├┤    │ ├────────────────────────┤
                             ╵└────┴─┘                        ╵
                             └                                            ┘
                             6.41 ms           11.08 ms            15.74 ms

summary
  js medium (experiment)
   1.04x faster than js medium (control)

------------------------------------------- -------------------------------
js large (control)             3.32 ms/iter   3.02 ms  █                   
                       (2.63 ms … 11.48 ms)   7.98 ms ▅█                   
                    (223.09 kb …   3.23 mb)   1.46 mb ██▂▃▂▁▁▂▂▁▁▁▂▂▁▁▁▁▁▁▁

js large (experiment)          3.07 ms/iter   2.84 ms  █                   
                        (2.52 ms … 8.00 ms)   6.45 ms  █                   
                    (164.08 kb …   2.73 mb)   1.44 mb ▇█▄▁▂▂▂▂▁▂▁▂▁▁▁▁▂▁▁▁▁

                             ┌                                            ┐
                              ╷┌────┬                                     ╷
          js large (control)  ├┤    │─────────────────────────────────────┤
                              ╵└────┴                                     ╵
                             ╷┌───┬                          ╷
       js large (experiment) ├┤   │──────────────────────────┤
                             ╵└───┴                          ╵
                             └                                            ┘
                             2.52 ms            5.25 ms             7.98 ms

summary
  js large (experiment)
   1.08x faster than js large (control)

------------------------------------------- -------------------------------
gjs small (control)            1.26 ms/iter   1.15 ms █                    
                        (1.09 ms … 7.04 ms)   6.11 ms █                    
                    (196.31 kb …   1.66 mb)   1.06 mb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gjs small (experiment)         1.25 ms/iter   1.13 ms █                    
                        (1.10 ms … 7.08 ms)   6.13 ms █                    
                    (354.58 kb …   1.60 mb)   1.06 mb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ┌─┬                                          ╷
         gjs small (control) │ │──────────────────────────────────────────┤
                             └─┴                                          ╵
                             ┌┬                                           ╷
      gjs small (experiment) ││───────────────────────────────────────────┤
                             └┴                                           ╵
                             └                                            ┘
                             1.09 ms            3.61 ms             6.13 ms

summary
  gjs small (experiment)
   1.01x faster than gjs small (control)

------------------------------------------- -------------------------------
gjs medium (control)         612.49 µs/iter 566.01 µs █                    
                      (537.54 µs … 6.58 ms)   3.30 ms █                    
                    ( 74.88 kb …   1.12 mb) 540.05 kb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gjs medium (experiment)      609.27 µs/iter 566.30 µs █                    
                      (538.84 µs … 5.98 ms)   1.65 ms █                    
                    ( 54.62 kb …   1.13 mb) 541.26 kb █▇▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ┌┬                                           ╷
        gjs medium (control) ││───────────────────────────────────────────┤
                             └┴                                           ╵
                             ┌┬                ╷
     gjs medium (experiment) ││────────────────┤
                             └┴                ╵
                             └                                            ┘
                             537.54 µs           1.92 ms            3.30 ms

summary
  gjs medium (experiment)
   1.01x faster than gjs medium (control)

------------------------------------------- -------------------------------
gjs large (control)          249.35 µs/iter 229.46 µs  █                   
                      (214.50 µs … 6.09 ms) 354.33 µs  █▂                  
                    (180.23 kb …   1.37 mb) 217.27 kb ███▇▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gjs large (experiment)       241.34 µs/iter 226.54 µs  █                   
                      (212.98 µs … 5.76 ms) 299.31 µs  █▃                  
                    (170.18 kb … 933.98 kb) 216.66 kb ▃██▃▇▃▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ╷ ┌─────────┬                                ╷
         gjs large (control) ├─┤         │────────────────────────────────┤
                             ╵ └─────────┴                                ╵
                             ╷┌───────┬                 ╷
      gjs large (experiment) ├┤       │─────────────────┤
                             ╵└───────┴                 ╵
                             └                                            ┘
                             212.98 µs         283.66 µs          354.33 µs

summary
  gjs large (experiment)
   1.03x faster than gjs large (control)

------------------------------------------- -------------------------------
gts small (control)            1.21 ms/iter   1.12 ms █                    
                        (1.09 ms … 6.73 ms)   6.12 ms █                    
                    (182.22 kb …   1.57 mb)   1.06 mb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gts small (experiment)         1.22 ms/iter   1.12 ms █                    
                        (1.09 ms … 7.24 ms)   6.10 ms █                    
                    (220.07 kb …   1.50 mb)   1.05 mb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ┌┬                                           ╷
         gts small (control) ││───────────────────────────────────────────┤
                             └┴                                           ╵
                             ┌┬                                           ╷
      gts small (experiment) ││───────────────────────────────────────────┤
                             └┴                                           ╵
                             └                                            ┘
                             1.09 ms            3.60 ms             6.12 ms

summary
  gts small (control)
   1.01x faster than gts small (experiment)

------------------------------------------- -------------------------------
gts medium (control)         609.35 µs/iter 560.96 µs █                    
                      (537.27 µs … 6.41 ms)   1.64 ms █                    
                    (171.29 kb …   1.26 mb) 542.33 kb █▄▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gts medium (experiment)      610.67 µs/iter 559.43 µs █                    
                      (534.78 µs … 6.68 ms)   2.96 ms █                    
                    ( 85.02 kb …   1.04 mb) 540.74 kb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ┌┬                  ╷
        gts medium (control) ││──────────────────┤
                             └┴                  ╵
                             ┌┬                                           ╷
     gts medium (experiment) ││───────────────────────────────────────────┤
                             └┴                                           ╵
                             └                                            ┘
                             534.78 µs           1.75 ms            2.96 ms

summary
  gts medium (control)
   1x faster than gts medium (experiment)

------------------------------------------- -------------------------------
gts large (control)          244.45 µs/iter 226.50 µs  █                   
                      (213.02 µs … 6.39 ms) 310.08 µs  █                   
                    ( 85.52 kb …   1.00 mb) 217.19 kb ▄██▅▆▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gts large (experiment)       253.65 µs/iter 228.13 µs █                    
                      (212.89 µs … 5.78 ms) 682.12 µs █                    
                    (183.88 kb …   1.37 mb) 216.96 kb ██▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ┌──┬     ╷
         gts large (control) │  │─────┤
                             └──┴     ╵
                             ┌───┬                                        ╷
      gts large (experiment) │   │────────────────────────────────────────┤
                             └───┴                                        ╵
                             └                                            ┘
                             212.89 µs         447.50 µs          682.12 µs

summary
  gts large (control)
   1.04x faster than gts large (experiment)