Failed to flatten: unknown variant `transient`

[mattstam]

Component

Forge

Have you ensured that all of these are up to date?

• Foundry
• Foundryup

What version of Foundry are you on?

1.2.3-stable

What version of Foundryup are you on?

1.2.3-stable

What command(s) is the bug in?

forge flatten

Operating System

macOS (Apple Silicon)

Describe the bug

I cannot flatten / verify my contract, which uses the solc 0.8.28+ transient keyword for storage variables.

To reproduce, you can try running on this repo which has transient used here.

[mattsse]

what's the version?
can you try bumping?

this should be fixed, can't repro

[0xrusowsky]

@mattstam can you provide more info to reproduce please?

[mattstam]

@mattsse @0xrusowsky Here is reproduction using the latest version available from foundryup (1.2.3-stable) and using the repo linked:

foundryup


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 ╔═╗ ╔═╗ ╦ ╦ ╔╗╔ ╔╦╗ ╦═╗ ╦ ╦         Portable and modular toolkit
 ╠╣  ║ ║ ║ ║ ║║║  ║║ ╠╦╝ ╚╦╝    for Ethereum Application Development
 ╚   ╚═╝ ╚═╝ ╝╚╝ ═╩╝ ╩╚═  ╩                 written in Rust.

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Repo       : https://github.com/foundry-rs/foundry
Book       : https://book.getfoundry.sh/
Chat       : https://t.me/foundry_rs/
Support    : https://t.me/foundry_support/
Contribute : https://github.com/foundry-rs/foundry/blob/master/CONTRIBUTING.md

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foundryup: installing foundry (version stable, tag stable)
foundryup: downloading forge, cast, anvil, and chisel for stable version
########################### 100.0%
x forge
x cast
x anvil
x chisel
foundryup: downloading manpages
########################### 100.0%
foundryup: use - forge 1.2.3-stable (a813a2cee7 2025-06-08T15:42:50.507050000Z)
foundryup: use - cast 1.2.3-stable (a813a2cee7 2025-06-08T15:42:50.507050000Z)
foundryup: use - anvil 1.2.3-stable (a813a2cee7 2025-06-08T15:42:50.507050000Z)
foundryup: use - chisel 1.2.3-stable (a813a2cee7 2025-06-08T15:42:50.507050000Z)

forge flatten src/SuccinctStaking.sol   
Error: Failed to flatten: unknown variant `transient`, expected one of `calldata`, `default`, `memory`, `storage` at line 1 column 16065

[zerosnacks]

Confirming this has been fixed in the latest nightly (foundryup -i nightly), will be included in the next stable release

forge flatten src/SuccinctStaking.sol   

now passes succesfully