[NullVoxPopuli]

Important

One upstream blocker remains: microsoft/TypeScript#64828 (go-to-definition on a .gts specifier). Its test is marked todo, so CI is green. Everything else is done.

Libraries can now emit counter.d.ts instead of counter.d.gts.ts, so declarations/ matches dist/ file for file. This uses the new outputExtensions option from microsoft/TypeScript#64581, which fixes microsoft/TypeScript#64053.

Changes

• examples/cli-library-v2: sets outputExtensions: { ".gts": ".js", ".gjs": ".js" } and rewriteRelativeImportExtensions: true. The emitted index.d.ts now says from './components/counter.js', and the ./* → ./declarations/*.d.ts export works for every module. I removed the README note saying it didn't.
• README: new "Publishing a library" section. MIGRATING_FROM_TS6.md links the #64053 item to it.
• Test: a new declaration-output-extensions fixture checks that Greeting.d.ts is emitted and Greeting.d.gts.ts is not.
• Bumps every TS 7 pin from 7.1.0-dev.20260821.1 to 7.1.0-dev.20261029.1.
• Root ember-source is now 7.5.0-beta.1. See the @extends section.
• Rebased on v0.4.0.

Why the mapper's package.json doesn't set a default

typescript.contentMapper.outputExtensions can go in the mapper's package.json, but I didn't add it:

• Any outputExtensions requires rewriteRelativeImportExtensions. Without it, tsc reports TS18120, even with --noEmit.
• With the flag on, both example apps fail with TS2877. Their extension imports aren't relative (#app/..., cli-app/...), so they can't be rewritten.
• So a default would break every app on upgrade. Apps could opt out with "outputExtensions": {}, but libraries are the ones that emit.

The other manifest fields don't help either: compilerOptions only lists which options get forwarded to the mapper. It can't set them.

Upstream status

@extends over Component.extend(Mixin): fixed in ember-source 7.5.0-beta.1

microsoft/TypeScript#64072 applies the tag's type arguments to the call's return type. Before emberjs/ember.js#21727, Component.extend(Evented) returned a constructor that is not generic. That gave TS2508, and the signature was lost.

• [BUGFIX] Keep generic classes generic through extend() emberjs/ember.js#21727 merged and shipped in ember-source 7.5.0-beta.1.
• With it, classic-mixin.gjs and jsdoc-extends-expression-heritage.gts have no errors. The upstream-differences snapshot no longer lists them.
• The docs say to use 7.5.0-beta.1 or newer, or a sibling declaration file on older versions.
• JSDoc @extends signature is lost for classic components with expression heritage (Component.extend(Mixin)) #12 can close when 7.5.0 is stable.

Go-to-definition on a .gts specifier: still broken

test/lsp.js "go to definition from a .ts import into a .gts module" returns []. The test is marked todo with the issue link.

• Reported as Content mappers: go-to-definition on an module specifier returns nothing when the target file has more than one span-map segment microsoft/TypeScript#64828. It has a smaller repro with no Ember and no Glint.
• It breaks on export ... from and on non-relative imports, such as paths aliases. Relative import ... from works.
• Caused by #63936 (Content mappers round 2): last good nightly 20260821.1, first bad 20260822.1.
• No mapper output can fix it. TS needs one span-map segment to cover the whole target file.
• Still broken on 20261029.1 and on 7.1.0-beta.

Tracking: #23

🤖 Generated with Claude Code

[github-actions]

🏎️ Benchmark Comparison

	Benchmark	Control (p50)	Experiment (p50)	Δ	Noise
⚪	transform	586.69 ms	591.77 ms	+0.9%	±5.0%
⚪	server 8-in-flight	645.73 ms	647.29 ms	+0.2%	±1.9%
⚪	tsc total	2982.00 ms	2959.00 ms	-0.8%	±3.1%
⚪	tsc mapper wait	2950.00 ms	2923.00 ms	-0.9%	±2.7%

🟢 faster · 🔴 slower · 🟠 slightly slower · ⚪ within 2% or within round-to-round noise

Full mitata output

clk: ~3.08 GHz
cpu: AMD EPYC 7763 64-Core Processor
runtime: node 24.22.1 (x64-linux)

benchmark                   avg (min … max) p75 / p99    (min … top 1%)
------------------------------------------- -------------------------------
transform (control)          604.85 ms/iter 617.03 ms   █          █ ██    
                    (572.53 ms … 648.88 ms) 627.88 ms ▅ █▅   ▅ ▅ ▅ █ ██▅  ▅
                    (  2.24 mb …  71.80 mb)  43.48 mb █▁██▁▁▁█▁█▁█▁█▁███▁▁█

server 8-in-flight (control) 657.81 ms/iter 663.69 ms █                    
                    (638.33 ms … 701.32 ms) 675.31 ms █  ▅▅▅▅▅▅ ▅▅ ▅▅ ▅ ▅ ▅
                    (  9.61 mb …   9.70 mb)   9.67 mb █▁▁██████▁██▁██▁█▁█▁█

━━━ round 1/3: mapper experiment (core 2) ━━━

clk: ~3.09 GHz
cpu: AMD EPYC 7763 64-Core Processor
runtime: node 24.22.1 (x64-linux)

benchmark                      avg (min … max) p75 / p99    (min … top 1%)
---------------------------------------------- -------------------------------
transform (experiment)          592.14 ms/iter 604.43 ms     █                
                       (560.78 ms … 638.69 ms) 635.72 ms █ █ █     █ █        
                       (177.96 kb …  68.37 mb)  42.07 mb ███▁█▁▁▁▁▁█▁█▁█▁▁▁▁██

server 8-in-flight (experiment) 651.90 ms/iter 666.60 ms   █                  
                       (629.03 ms … 676.57 ms) 675.32 ms   █                 █
                       (  9.66 mb …   9.70 mb)   9.68 mb █▁████▁▁▁██▁▁██▁█▁█▁█

━━━ round 1/3: tsc control ━━━

tsc: 36 files (6 fixtures × 6), 3 runs after warm-up
  run 1: total 2.94s, mapper wait 2.91s
  run 2: total 3.05s, mapper wait 3.02s
  run 3: total 3.05s, mapper wait 3.02s
  p50: total 3.05s, mapper wait 3.02s

━━━ round 1/3: tsc experiment ━━━

tsc: 36 files (6 fixtures × 6), 3 runs after warm-up
  run 1: total 2.91s, mapper wait 2.88s
  run 2: total 2.96s, mapper wait 2.92s
  run 3: total 2.97s, mapper wait 2.94s
  p50: total 2.96s, mapper wait 2.92s

━━━ round 2/3: mapper control (core 2) ━━━

clk: ~3.09 GHz
cpu: AMD EPYC 7763 64-Core Processor
runtime: node 24.22.1 (x64-linux)

benchmark                   avg (min … max) p75 / p99    (min … top 1%)
------------------------------------------- -------------------------------
transform (control)          583.93 ms/iter 601.67 ms    █    █            
                    (549.20 ms … 614.19 ms) 613.87 ms ▅ ▅█ ▅  █▅ ▅  ▅▅▅ ▅▅▅
                    (  1.33 mb …  71.79 mb)  42.44 mb █▁██▁█▁▁██▁█▁▁███▁███

server 8-in-flight (control) 650.26 ms/iter 659.00 ms              █       
                    (626.61 ms … 681.64 ms) 675.82 ms    █ █  █    █       
                    (  9.66 mb …   9.70 mb)   9.68 mb █▁██▁█▁▁█▁█▁██▁▁▁▁█▁█

━━━ round 2/3: mapper experiment (core 0) ━━━

clk: ~3.10 GHz
cpu: AMD EPYC 7763 64-Core Processor
runtime: node 24.22.1 (x64-linux)

benchmark                      avg (min … max) p75 / p99    (min … top 1%)
---------------------------------------------- -------------------------------
transform (experiment)          601.76 ms/iter 610.42 ms    █  █ █ █    █     
                       (558.38 ms … 651.64 ms) 648.76 ms ▅  █  █▅█ █▅▅  █    ▅
                       (  3.28 mb …  70.08 mb)  34.16 mb █▁▁█▁▁███▁███▁▁█▁▁▁▁█

server 8-in-flight (experiment) 649.72 ms/iter 658.80 ms         █            
                       (625.45 ms … 681.22 ms) 679.24 ms  █      █            
                       (  9.66 mb …   9.70 mb)   9.68 mb ██▁▁██▁▁███████▁▁▁▁▁█

━━━ round 2/3: tsc experiment ━━━

tsc: 36 files (6 fixtures × 6), 3 runs after warm-up
  run 1: total 2.99s, mapper wait 2.97s
  run 2: total 3.09s, mapper wait 3.06s
  run 3: total 2.95s, mapper wait 2.92s
  p50: total 2.99s, mapper wait 2.97s

━━━ round 2/3: tsc control ━━━

tsc: 36 files (6 fixtures × 6), 3 runs after warm-up
  run 1: total 2.92s, mapper wait 2.88s
  run 2: total 3.08s, mapper wait 3.02s
  run 3: total 2.96s, mapper wait 2.94s
  p50: total 2.96s, mapper wait 2.94s

━━━ round 3/3: mapper control (core 0) ━━━

clk: ~3.10 GHz
cpu: AMD EPYC 7763 64-Core Processor
runtime: node 24.22.1 (x64-linux)

benchmark                   avg (min … max) p75 / p99    (min … top 1%)
------------------------------------------- -------------------------------
transform (control)          587.92 ms/iter 603.30 ms                █    █
                    (551.74 ms … 633.79 ms) 616.38 ms ▅▅▅▅ ▅▅▅   ▅  ▅█▅  ▅█
                    (  1.76 mb …  71.27 mb)  35.46 mb ████▁███▁▁▁█▁▁███▁▁██

server 8-in-flight (control) 641.39 ms/iter 647.07 ms           █          
                    (620.68 ms … 664.11 ms) 662.77 ms        ▅  █          
                    (  9.66 mb …   9.70 mb)   9.68 mb ▇▁▁▇▇▁▇█▇▁█▁▁▇▇▁▁▇▁▁▇

━━━ round 3/3: mapper experiment (core 2) ━━━

clk: ~3.10 GHz
cpu: AMD EPYC 7763 64-Core Processor
runtime: node 24.22.1 (x64-linux)

benchmark                      avg (min … max) p75 / p99    (min … top 1%)
---------------------------------------------- -------------------------------
transform (experiment)          598.58 ms/iter 610.31 ms    ██                
                       (557.75 ms … 670.48 ms) 636.57 ms ▅  ██  ▅▅▅▅▅▅▅  ▅▅  ▅
                       (  2.81 mb …  68.44 mb)  42.67 mb █▁▁██▁▁███████▁▁██▁▁█

server 8-in-flight (experiment) 633.59 ms/iter 653.37 ms      █        █  █ █ 
                       (577.07 ms … 669.87 ms) 661.40 ms ▅    █▅    ▅▅ █ ▅█▅█▅
                       (  9.66 mb …   9.70 mb)   9.68 mb █▁▁▁▁██▁▁▁▁██▁█▁█████

━━━ round 3/3: tsc control ━━━

tsc: 36 files (6 fixtures × 6), 3 runs after warm-up
  run 1: total 2.98s, mapper wait 2.95s
  run 2: total 3.01s, mapper wait 2.98s
  run 3: total 2.94s, mapper wait 2.92s
  p50: total 2.98s, mapper wait 2.95s

━━━ round 3/3: tsc experiment ━━━

tsc: 36 files (6 fixtures × 6), 3 runs after warm-up
  run 1: total 2.89s, mapper wait 2.86s
  run 2: total 3.22s, mapper wait 3.18s
  run 3: total 2.92s, mapper wait 2.89s
  p50: total 2.92s, mapper wait 2.89s