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template-no-extra-mut-helper-argument: applies to strict mode, and stop recommending (action) - #2841

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nvp/mut-helper-rule-is-not-hbs-only
Aug 17, 2026
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template-no-extra-mut-helper-argument: applies to strict mode, and stop recommending (action)#2841
evoactivity merged 2 commits into
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nvp/mut-helper-rule-is-not-hbs-only

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@NullVoxPopuli

@NullVoxPopuli NullVoxPopuli commented Aug 17, 2026 •
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templateMode: 'loose' is wrong on this rule. mut is an ambient Glimmer keyword, so (mut a b) needs no import and is reachable in a gjs/gts template. The rule has no strict-mode guard and reports there today.

Verified by linting a .gjs file with only this rule on:

const Foo = <template>{{yield (mut @a @b)}}</template>;
ember/template-no-extra-mut-helper-argument

Changes templateMode to both, which drops the "HBS Only" note from the docs, and adds a gjs test case so the behavior is pinned.

Found while implementing RFC #1217 in #2840: the RFC puts this rule in Appendix A (applies to strict mode) while the code claimed hbs-only. The RFC is right.

🤖 Generated with Claude Code

Also: the message pointed at removed API

The report told people to write (action (mut attr) value), and {{action}} is gone from ember-source. It now points at (fn (mut attr) value). The docs examples and test fixtures move to fn and {{on "click" ...}} for the same reason.

@NullVoxPopuli @claude
template-no-extra-mut-helper-argument is not hbs-only
b6d959e 
`mut` is an ambient strict-mode keyword, so `(mut a b)` is reachable in
gjs/gts and the rule reports there. Adds a gjs test case.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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github-actions Bot commented Aug 17, 2026 •
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🏎️ Benchmark Comparison

Benchmark Control (p50) Experiment (p50) Δ
⚪ js small 10.57 ms 10.52 ms -0.4%
🟠 js medium 5.14 ms 5.31 ms +3.3%
⚪ js large 2.10 ms 2.08 ms -1.2%
⚪ gjs small 870.05 µs 869.59 µs -0.1%
⚪ gjs medium 433.86 µs 431.61 µs -0.5%
⚪ gjs large 171.25 µs 172.39 µs +0.7%
⚪ gts small 858.58 µs 857.76 µs -0.1%
⚪ gts medium 431.11 µs 432.71 µs +0.4%
⚪ gts large 171.28 µs 171.22 µs -0.0%

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

Full mitata output 
clk: ~3.50 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)            12.23 ms/iter  13.54 ms ██ ▃                 
                       (8.71 ms … 25.14 ms)  21.91 ms ██▃█ ▃ ▃             
                    (  6.08 mb …  10.79 mb)   7.21 mb ████▁███▆▆▄▁▁▄▁▁▆▁▁▄▆

js small (experiment)         11.12 ms/iter  12.26 ms █                    
                       (9.37 ms … 16.26 ms)  15.83 ms ██▆ █    ▃           
                    (  6.59 mb …   8.04 mb)   6.88 mb █████▇▃▁▃█▁▇▅▃▁▅▁▃▃▁▃

                             ┌                                            ┐
                             ╷┌──────────┬───┐                            ╷
          js small (control) ├┤          │   ├────────────────────────────┤
                             ╵└──────────┴───┘                            ╵
                               ╷┌────┬───┐           ╷
       js small (experiment)   ├┤    │   ├───────────┤
                               ╵└────┴───┘           ╵
                             └                                            ┘
                             8.71 ms           15.31 ms            21.91 ms

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

------------------------------------------- -------------------------------
js medium (control)            5.62 ms/iter   5.72 ms █▇                   
                       (4.84 ms … 11.24 ms)   9.44 ms ██                   
                    (  3.33 mb …   3.99 mb)   3.54 mb ███▇▄▄▄▃▃▂▁▂▁▂▂▂▁▂▁▂▂

js medium (experiment)         5.89 ms/iter   6.04 ms █ ▆                  
                       (4.44 ms … 14.64 ms)  11.61 ms █ █▆                 
                    (  1.41 mb …   5.89 mb)   3.51 mb █▅███▃▇▃▃▅▂▂▁▂▁▁▃▁▂▂▂

                             ┌                                            ┐
                               ╷┌───┬┐                      ╷
         js medium (control)   ├┤   │├──────────────────────┤
                               ╵└───┴┘                      ╵
                             ╷┌───────┬┐                                  ╷
      js medium (experiment) ├┤       │├──────────────────────────────────┤
                             ╵└───────┴┘                                  ╵
                             └                                            ┘
                             4.44 ms            8.03 ms            11.61 ms

summary
  js medium (control)
   1.05x faster than js medium (experiment)

------------------------------------------- -------------------------------
js large (control)             2.33 ms/iter   2.19 ms ▂█                   
                        (1.96 ms … 5.84 ms)   5.09 ms ██                   
                    (128.83 kb …   2.77 mb)   1.43 mb ██▃▃▃▂▂▂▁▂▂▁▁▁▁▁▂▁▁▁▁

js large (experiment)          2.30 ms/iter   2.17 ms  █                   
                        (1.93 ms … 5.31 ms)   5.24 ms ▇█                   
                    (239.03 kb …   2.61 mb)   1.44 mb ██▄▂▂▂▂▁▂▁▁▁▁▁▁▂▁▁▁▁▁

                             ┌                                            ┐
                             ╷┌───┬                                     ╷
          js large (control) ├┤   │─────────────────────────────────────┤
                             ╵└───┴                                     ╵
                             ╷┌───┬                                       ╷
       js large (experiment) ├┤   │───────────────────────────────────────┤
                             ╵└───┴                                       ╵
                             └                                            ┘
                             1.93 ms            3.59 ms             5.24 ms

summary
  js large (experiment)
   1.01x faster than js large (control)

------------------------------------------- -------------------------------
gjs small (control)          978.19 µs/iter 883.14 µs █                    
                      (839.81 µs … 5.49 ms)   5.32 ms █                    
                    (551.12 kb …   2.16 mb)   1.06 mb █▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gjs small (experiment)       964.73 µs/iter 879.41 µs █                    
                      (844.11 µs … 6.06 ms)   5.55 ms █                    
                    (582.86 kb …   2.24 mb)   1.06 mb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ┌┬                                         ╷
         gjs small (control) ││─────────────────────────────────────────┤
                             └┴                                         ╵
                             ┌┬                                           ╷
      gjs small (experiment) ││───────────────────────────────────────────┤
                             └┴                                           ╵
                             └                                            ┘
                             839.81 µs           3.19 ms            5.55 ms

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

------------------------------------------- -------------------------------
gjs medium (control)         478.59 µs/iter 439.79 µs █                    
                      (419.96 µs … 5.45 ms)   1.08 ms █▆                   
                    ( 34.29 kb …   1.04 mb) 539.92 kb ██▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gjs medium (experiment)      471.19 µs/iter 437.07 µs █                    
                      (418.50 µs … 4.70 ms)   1.04 ms █▇                   
                    ( 34.12 kb …   1.04 mb) 540.14 kb ██▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ╷┌──┬                                        ╷
        gjs medium (control) ├┤  │────────────────────────────────────────┤
                             ╵└──┴                                        ╵
                             ╷┌──┬                                     ╷
     gjs medium (experiment) ├┤  │─────────────────────────────────────┤
                             ╵└──┴                                     ╵
                             └                                            ┘
                             418.50 µs          750.46 µs           1.08 ms

summary
  gjs medium (experiment)
   1.02x faster than gjs medium (control)

------------------------------------------- -------------------------------
gjs large (control)          190.14 µs/iter 174.24 µs   █                  
                      (166.08 µs … 4.90 ms) 216.60 µs  ██                  
                    (129.04 kb … 769.91 kb) 216.28 kb ▂███▃▅▅▃▂▁▁▁▁▁▁▁▁▁▁▁▁

gjs large (experiment)       191.29 µs/iter 175.64 µs  █▇                  
                      (166.91 µs … 4.90 ms) 225.69 µs  ██                  
                    (180.16 kb …   1.37 mb) 216.51 kb ▃██▇▅▆▃▂▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ╷  ┌──────────────┬                   ╷
         gjs large (control) ├──┤              │───────────────────┤
                             ╵  └──────────────┴                   ╵
                              ╷ ┌───────────────┬                         ╷
      gjs large (experiment)  ├─┤               │─────────────────────────┤
                              ╵ └───────────────┴                         ╵
                             └                                            ┘
                             166.08 µs         195.88 µs          225.69 µs

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

------------------------------------------- -------------------------------
gts small (control)          939.60 µs/iter 867.11 µs █                    
                      (836.92 µs … 5.33 ms)   4.99 ms █                    
                    (721.79 kb …   2.24 mb)   1.06 mb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gts small (experiment)       931.39 µs/iter 866.90 µs █                    
                      (836.97 µs … 5.47 ms)   4.97 ms █                    
                    (  1.02 mb …   2.21 mb)   1.06 mb █▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ┌┬                                           ╷
         gts small (control) ││───────────────────────────────────────────┤
                             └┴                                           ╵
                             ┌┬                                           ╷
      gts small (experiment) ││───────────────────────────────────────────┤
                             └┴                                           ╵
                             └                                            ┘
                             836.92 µs           2.92 ms            4.99 ms

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

------------------------------------------- -------------------------------
gts medium (control)         473.03 µs/iter 436.96 µs ▄█                   
                      (418.82 µs … 5.20 ms) 822.12 µs ██                   
                    (507.66 kb …   1.59 mb) 540.60 kb ██▃▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

gts medium (experiment)      476.57 µs/iter 439.79 µs █▂                   
                      (418.50 µs … 5.53 ms)   1.04 ms ██                   
                    (104.66 kb …   1.63 mb) 540.46 kb ██▂▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ╷┌──┬                        ╷
        gts medium (control) ├┤  │────────────────────────┤
                             ╵└──┴                        ╵
                             ╷┌──┬                                        ╷
     gts medium (experiment) ├┤  │────────────────────────────────────────┤
                             ╵└──┴                                        ╵
                             └                                            ┘
                             418.50 µs          728.58 µs           1.04 ms

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

------------------------------------------- -------------------------------
gts large (control)          190.75 µs/iter 175.02 µs  █▇                  
                      (166.26 µs … 4.97 ms) 216.76 µs  ██▂                 
                    ( 86.81 kb … 808.51 kb) 216.31 kb ▃███▅▆▅▃▂▁▁▁▁▁▁▁▁▁▁▁▁

gts large (experiment)       189.49 µs/iter 174.18 µs  ▅█                  
                      (166.32 µs … 5.14 ms) 213.85 µs  ██▄                 
                    (170.20 kb …   1.37 mb) 216.45 kb ▃███▄▄▆▄▂▁▁▁▁▁▁▁▁▁▁▁▁

                             ┌                                            ┐
                             ╷  ┌──────────────────┬                      ╷
         gts large (control) ├──┤                  │──────────────────────┤
                             ╵  └──────────────────┴                      ╵
                             ╷  ┌─────────────────┬                    ╷
      gts large (experiment) ├──┤                 │────────────────────┤
                             ╵  └─────────────────┴                    ╵
                             └                                            ┘
                             166.26 µs         191.51 µs          216.76 µs

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

@NullVoxPopuli NullVoxPopuli mentioned this pull request Aug 17, 2026
Draft
@NullVoxPopuli @claude
Stop recommending (action) in the mut message
a76df40 
{{action}} was removed from ember-source, so the fix the message told
people to write no longer exists. Points at (fn (mut attr) value) and
updates the docs and fixtures to match.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
@NullVoxPopuli NullVoxPopuli changed the title template-no-extra-mut-helper-argument is not hbs-only template-no-extra-mut-helper-argument: applies to strict mode, and stop recommending (action) Aug 17, 2026
@evoactivity
evoactivity merged commit f236dfe into master Aug 17, 2026
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@evoactivity
evoactivity deleted the nvp/mut-helper-rule-is-not-hbs-only branch August 17, 2026 21:09
@github-actions github-actions Bot mentioned this pull request Aug 17, 2026
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@NullVoxPopuli @evoactivity