Add decorator and setting to set `hints.mostly-unused` #4243

landonxjames · 2025-08-01T19:02:23Z

Motivation and Context

Continuing the work started in #4208, the new feature we are utilizing is explained in https://blog.rust-lang.org/inside-rust/2025/07/15/call-for-testing-hint-mostly-unused

Description

Add a new ManifestHintsDecorator that allows adding a [hints] section to a generated Cargo.toml. This also introduces a new optional entry in smithy-build.json, hintsMostlyUnusedList that allows indicating which crates this should be enabled for. Currently this is only enabled for aws-sdk-s3, aws-sdk-dynamodb, and aws-sdk-ec2.

Testing

I tested both debug and release builds of the crates, with and without the hint on an M1 Macbook Pro. You can see the full data below, but the general outcome is that release builds are ~50% faster with the hint and debug builds are ~40% faster. A release build of the aws-sdk-ec2 crate went from 124.1s without the hint to 59.1s with it.

Expand To See Test Data

All tests run after deleting the `target/` dir

Debug No Hint

cargo build --timings

||Unit|Total|Codegen|Features|
|---|---|---|---|---|
|1.|aws-sdk-ec2 v0.0.0-local|104.8s|27.9s (27%)|default, default-https-client, rt-tokio, rustls|
|2.|aws-lc-sys v0.30.0 build script (run)|26.1s||prebuilt-nasm|
|3.|aws-sdk-s3 v0.0.0-local|21.2s|5.2s (24%)|default, default-https-client, rt-tokio, rustls, sigv4a|
|4.|aws-sdk-dynamodb v0.0.0-local|13.7s|4.0s (29%)|default, default-https-client, rt-tokio, rustls|

Unit	Total	Codegen
aws-sdk-ec2	104.8s	27.9s (27%)
aws-sdk-s3	21.2s	5.2s (24%)
aws-sdk-dynamodb	13.7s	4.0s (29%)

Debug Hint

cargo +nightly -Zprofile-hint-mostly-unused build --timings

||Unit|Total|Codegen|Features|
|---|---|---|---|---|
|1.|aws-sdk-ec2 v0.0.0-local|66.4s|2.4s (4%)|default, default-https-client, rt-tokio, rustls|
|2.|aws-lc-sys v0.30.0 build script (run)|25.0s||prebuilt-nasm|
|3.|aws-sdk-s3 v0.0.0-local|14.6s|0.8s (5%)|default, default-https-client, rt-tokio, rustls, sigv4a|
|4.|aws-sdk-dynamodb v0.0.0-local|9.1s|0.4s (4%)|default, default-https-client, rt-tokio, rustls|

Unit	Total	Codegen
aws-sdk-ec2	66.4s	2.4s (4%)
aws-sdk-s3	14.6s	0.8s (5%)
aws-sdk-dynamodb	9.1s	0.4s (4%)

Release No Hint

cargo build --timings --release

||Unit|Total|Codegen|Features|
|---|---|---|---|---|
|1.|aws-sdk-ec2 v0.0.0-local|124.1s|54.3s (44%)|default, default-https-client, rt-tokio, rustls|
|2.|aws-lc-sys v0.30.0 build script (run)|34.3s||prebuilt-nasm|
|3.|aws-sdk-s3 v0.0.0-local|28.5s|11.4s (40%)|default, default-https-client, rt-tokio, rustls, sigv4a|
|4.|aws-sdk-dynamodb v0.0.0-local|19.3s|8.5s (44%)|default, default-https-client, rt-tokio, rustls|

Unit	Total	Codegen
aws-sdk-ec2	124.1s	54.3s (44%)
aws-sdk-s3	28.5s	11.4s (40%)
aws-sdk-dynamodb	19.3s	8.5s (44%)

Release Hint

cargo +nightly -Zprofile-hint-mostly-unused build --timings --release

||Unit|Total|Codegen|Features|
|---|---|---|---|---|
|1.|aws-sdk-ec2 v0.0.0-local|59.1s|1.0s (2%)|default, default-https-client, rt-tokio, rustls|
|2.|aws-lc-sys v0.30.0 build script (run)|34.4s||prebuilt-nasm|
|3.|aws-sdk-s3 v0.0.0-local|14.7s|0.4s (3%)|default, default-https-client, rt-tokio, rustls, sigv4a|
|4.|tokio v1.47.1|11.1s|7.3s (65%)|bytes, default, fs, full, io-std, io-util, libc, macros, mio, net, parking_lot, process, rt, rt-multi-thread, signal, signal-hook-registry, socket2, sync, time, tokio-macros|
|5.|aws-sdk-dynamodb v0.0.0-local|10.4s|0.4s (4%)|default, default-https-client, rt-tokio, rustls|

Unit	Total	Codegen
aws-sdk-ec2	59.1s	1.0s (2%)
aws-sdk-s3	14.7s	0.4s (3%)
aws-sdk-dynamodb	10.4s	0.4s (4%)

Checklist

For changes to the smithy-rs codegen or runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "client," "server," or both in the applies_to key.
For changes to the AWS SDK, generated SDK code, or SDK runtime crates, I have created a changelog entry Markdown file in the .changelog directory, specifying "aws-sdk-rust" in the applies_to key.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

landonxjames · 2025-08-01T19:03:24Z

...codegen/src/main/kotlin/software/amazon/smithy/rustsdk/customize/ServiceSpecificDecorator.kt

@@ -17,6 +17,14 @@ fun ClientCodegenDecorator.onlyApplyTo(serviceId: String): List<ClientCodegenDec
        },
    )

+/** Only apply this decorator to the given list of service IDs */


I didn't end up needing this after I moved the service list to gradle.properties, but seemed like it could be a useful utility in the future, so I left it.

github-actions · 2025-08-01T19:24:00Z

A new generated diff is ready to view.

AWS SDK (ignoring whitespace)
Client Test (ignoring whitespace)
No codegen difference in the Server Test
Server Test Python (ignoring whitespace)
No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

github-actions · 2025-08-01T20:17:17Z

A new generated diff is ready to view.

AWS SDK (ignoring whitespace)
No codegen difference in the Client Test
No codegen difference in the Server Test
No codegen difference in the Server Test Python
No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

ysaito1001

Excited to get this out the door!

BTW, people have also complained about aws-sdk-ssm in this issue. Should we consider adding it to the list of services?

landonxjames · 2025-08-01T21:29:09Z

Looks like this comment has a pretty good list, if we all feel comfortable with it I can add:

aws-sdk-ssm
aws-sd-cloudformation
aws-sdk-sns
aws-sdk-sqs

To the existing list

landonxjames · 2025-08-02T04:53:46Z

Added the discussed crates in 550bc3f, will do some quick bench marks on them to make sure it is beneficial.

The failing action (for generating diffs) has the error:

e: file:///home/build/workspace/smithy-rs/codegen-server/typescript/src/main/kotlin/software/amazon/smithy/rust/codegen/server/typescript/smithy/generators/TsServerEnumGenerator.kt:48:9 No value passed for parameter 'customizations'

Which makes me think it might be related to #4039 that was merged earlier today. Checking that PR it seems like the diff isn't generated for the CI run on forks, so CI there wouldn't have caught it.

joshtriplett · 2025-08-04T08:44:48Z

I would suggest also adding aws-sdk-sts.

Without the hint, a crate depending on aws-sdk-sts built in 41.26s.
With the hint, the same crate built in 36.30s.

aws/sdk/gradle.properties

...ient/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/ClientRustSettings.kt

github-actions · 2025-08-04T16:17:57Z

A new generated diff is ready to view.

AWS SDK (ignoring whitespace)
No codegen difference in the Client Test
No codegen difference in the Server Test
No codegen difference in the Server Test Python
No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

github-actions · 2025-08-04T21:13:29Z

A new generated diff is ready to view.

AWS SDK (ignoring whitespace)
No codegen difference in the Client Test
No codegen difference in the Server Test
No codegen difference in the Server Test Python
No codegen difference in the Server Test Typescript

A new doc preview is ready to view.

aajtodd · 2025-08-05T12:43:38Z

aws/sdk/gradle.properties

 aws.services=
+aws.services.hints.mostlyUnused=\


Probably want to remove this.

## Motivation and Context   ## Description  ## Testing    ---- _By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice._

Add decorator and setting to set hints.mostly-unused

ba98f30

landonxjames commented Aug 1, 2025

View reviewed changes

Merge branch 'main' into landonxjames/hint

653c84d

landonxjames added 2 commits August 1, 2025 13:57

Merge branch 'main' into landonxjames/hint

05ee5de

Add changelog entry

d45e041

landonxjames marked this pull request as ready for review August 1, 2025 21:06

landonxjames requested review from a team as code owners August 1, 2025 21:06

ysaito1001 approved these changes Aug 1, 2025

View reviewed changes

Add a few more crates with hints.mostly-unused

550bc3f

Fix bug with enum customizations in TsServer codegen

24d314f

aajtodd reviewed Aug 4, 2025

View reviewed changes

aws/sdk/gradle.properties Show resolved Hide resolved

...ient/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/ClientRustSettings.kt Outdated Show resolved Hide resolved

Merge branch 'main' into landonxjames/hint

abe99fc

landonxjames added 2 commits August 4, 2025 13:49

Remove hinstMostlyUnused from smithy-build.json

10a2c01

Merge branch 'main' into landonxjames/hint

4ef2984

landonxjames merged commit 1edaa7e into main Aug 4, 2025
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landonxjames deleted the landonxjames/hint branch August 4, 2025 21:39

landonxjames mentioned this pull request Aug 5, 2025

Use new hints.mostly-unused to speed up compilation #4208

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aajtodd reviewed Aug 5, 2025

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aws/sdk/gradle.properties

aws.services=

aws.services.hints.mostlyUnused=\

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Probably want to remove this.

landonxjames added a commit that referenced this pull request Aug 5, 2025

Cleanup missed property from #4243

d264489

landonxjames mentioned this pull request Aug 12, 2025

Compile time awslabs/aws-sdk-rust#113

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Motivation and Context

Description

Testing

Debug No Hint

Debug Hint

Release No Hint

Release Hint

Checklist

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