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#1572 in Magic Beans

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Foundry's configuration system allows you to configure it's tools the way you want while also providing with a sensible set of defaults.


Configurations can be arbitrarily namespaced by profiles. Foundry's default config is also named default, but can arbitrarily name and configure profiles as you like and set the FOUNDRY_PROFILE environment variable to the selected profile's name. This results in foundry's tools (forge) preferring the values in the profile with the named that's set in FOUNDRY_PROFILE. But all custom profiles inherit from the default profile.


Foundry's tools search for a foundry.toml or the filename in a FOUNDRY_CONFIG environment variable starting at the current working directory. If it is not found, the parent directory, its parent directory, and so on are searched until the file is found or the root is reached. But the typical location for the global foundry.toml would be ~/.foundry/foundry.toml, which is also checked. If the path set in FOUNDRY_CONFIG is absolute, no such search takes place and the absolute path is used directly.

In foundry.toml you can define multiple profiles, therefore the file is assumed to be nested, so each top-level key declares a profile and its values configure the profile.

The following is an example of what such a file might look like. This can also be obtained with forge config

## defaults for _all_ profiles
src = "src"
out = "out"
libs = ["lib"]
solc = "0.8.10" # to use a specific local solc install set the path as `solc = "<path to solc>/solc"`
eth-rpc-url = "https://mainnet.infura.io"

## set only when the `hardhat` profile is selected
src = "contracts"
out = "artifacts"
libs = ["node_modules"]

## set only when the `spells` profile is selected
## --snip-- more settings

Default profile

When determining the profile to use, Config considers the following sources in ascending priority order to read from and merge, at the per-key level:

  1. [Config::default()], which provides default values for all parameters.
  2. foundry.toml or TOML file path in FOUNDRY_CONFIG environment variable.
  3. FOUNDRY_ or DAPP_ prefixed environment variables.

The selected profile is the value of the FOUNDRY_PROFILE environment variable, or if it is not set, "default".

All Options

The following is a foundry.toml file with all configuration options set. See also /config/src/lib.rs and /cli/tests/it/config.rs.

## defaults for _all_ profiles
src = 'src'
test = 'test'
script = 'script'
out = 'out'
libs = ['lib']
auto_detect_remappings = true # recursive auto-detection of remappings
remappings = []
# list of libraries to link in the form of `<path to lib>:<lib name>:<address>`: `"src/MyLib.sol:MyLib:0x8De6DDbCd5053d32292AAA0D2105A32d108484a6"`
# the <path to lib> supports remappings
libraries = []
cache = true
cache_path = 'cache'
broadcast = 'broadcast'
# additional solc allow paths
allow_paths = []
# additional solc include paths
include_paths = []
force = false
evm_version = 'shanghai'
gas_reports = ['*']
gas_reports_ignore = []
## Sets the concrete solc version to use, this overrides the `auto_detect_solc` value
# solc = '0.8.10'
auto_detect_solc = true
offline = false
optimizer = true
optimizer_runs = 200
model_checker = { contracts = { 'a.sol' = [
], 'b.sol' = [
] }, engine = 'chc', targets = [
], timeout = 10000 }
verbosity = 0
eth_rpc_url = "https://example.com/"
# Setting this option enables decoding of error traces from mainnet deployed / verfied contracts via etherscan
etherscan_api_key = "YOURETHERSCANAPIKEY"
# ignore solc warnings for missing license and exceeded contract size
# known error codes are: ["unreachable", "unused-return", "unused-param", "unused-var", "code-size", "shadowing", "func-mutability", "license", "pragma-solidity", "virtual-interfaces", "same-varname"]
# additional warnings can be added using their numeric error code: ["license", 1337]
ignored_error_codes = ["license", "code-size"]
deny_warnings = false
match_test = "Foo"
no_match_test = "Bar"
match_contract = "Foo"
no_match_contract = "Bar"
match_path = "*/Foo*"
no_match_path = "*/Bar*"
ffi = false
# These are the default callers, generated using `address(uint160(uint256(keccak256("foundry default caller"))))`
sender = '0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38'
tx_origin = '0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38'
initial_balance = '0xffffffffffffffffffffffff'
block_number = 0
fork_block_number = 0
chain_id = 1
# NOTE due to a toml-rs limitation, this value needs to be a string if the desired gas limit exceeds `i64::MAX` (9223372036854775807)
# `gas_limit = "Max"` is equivalent to `gas_limit = "18446744073709551615"`
gas_limit = 9223372036854775807
gas_price = 0
block_base_fee_per_gas = 0
block_coinbase = '0x0000000000000000000000000000000000000000'
block_timestamp = 0
block_difficulty = 0
block_prevrandao = '0x0000000000000000000000000000000000000000'
block_gas_limit = 30000000
memory_limit = 33554432
extra_output = ["metadata"]
extra_output_files = []
names = false
sizes = false
via_ir = false
# caches storage retrieved locally for certain chains and endpoints
# can also be restricted to `chains = ["optimism", "mainnet"]`
# by default all endpoints will be cached, alternative options are "remote" for only caching non localhost endpoints and "<regex>"
# to disable storage caching entirely set `no_storage_caching = true`
rpc_storage_caching = { chains = "all", endpoints = "all" }
# this overrides `rpc_storage_caching` entirely
no_storage_caching = false
# Whether to store the referenced sources in the metadata as literal data.
use_literal_content = false
# use ipfs method to generate the metadata hash, solc's default.
# To not include the metadata hash, to allow for deterministic code: https://docs.soliditylang.org/en/latest/metadata.html, use "none"
bytecode_hash = "ipfs"
# Whether to append the metadata hash to the bytecode
cbor_metadata = true
# How to treat revert (and require) reason strings.
# Possible values are: "default", "strip", "debug" and "verboseDebug".
#  "default" does not inject compiler-generated revert strings and keeps user-supplied ones.
# "strip" removes all revert strings (if possible, i.e. if literals are used) keeping side-effects
# "debug" injects strings for compiler-generated internal reverts, implemented for ABI encoders V1 and V2 for now.
# "verboseDebug" even appends further information to user-supplied revert strings (not yet implemented)
revert_strings = "default"
# If this option is enabled, Solc is instructed to generate output (bytecode) only for the required contracts
# this can reduce compile time for `forge test` a bit but is considered experimental at this point.
sparse_mode = false
build_info = true
build_info_path = "build-info"
root = "root"
# Configures permissions for cheatcodes that touch the filesystem like `vm.writeFile`
# `access` restricts how the `path` can be accessed via cheatcodes
#    `read-write` | `true`   => `read` + `write` access allowed (`vm.readFile` + `vm.writeFile`)
#    `none`| `false` => no access
#    `read` => only read access (`vm.readFile`)
#    `write` => only write access (`vm.writeFile`)
# The `allowed_paths` further lists the paths that are considered, e.g. `./` represents the project root directory
# By default, only read access is granted to the project's out dir, so generated artifacts can be read by default
# following example enables read-write access for the project dir :
#       `fs_permissions = [{ access = "read-write", path = "./"}]`
fs_permissions = [{ access = "read", path = "./out"}]
runs = 256
max_test_rejects = 65536
seed = '0x3e8'
dictionary_weight = 40
include_storage = true
include_push_bytes = true

runs = 256
depth = 15
fail_on_revert = false
call_override = false
dictionary_weight = 80
include_storage = true
include_push_bytes = true
shrink_sequence = true

line_length = 100
tab_width = 2
bracket_spacing = true

Additional Optimizer settings

Optimizer components can be tweaked with the OptimizerDetails object:

See Compiler Input Description settings.optimizer.details

The optimizer_details (optimizerDetails also works) settings must be prefixed with the profile they correspond to: [profile.default.optimizer_details] belongs to the [profile.default] profile

constantOptimizer = true
yul = true
# this sets the `yulDetails` of the `optimizer_details` for the `default` profile
stackAllocation = true
optimizerSteps = 'dhfoDgvulfnTUtnIf'

RPC-Endpoints settings

The rpc_endpoints value accepts a list of alias = "<url|env var>" pairs.

The following example declares two pairs: The alias optimism references the endpoint URL directly. The alias mainnet references the environment variable RPC_MAINNET which holds the entire URL. The alias goerli references an endpoint that will be interpolated with the value the GOERLI_API_KEY holds.

Environment variables need to be wrapped in ${}

optimism = "https://optimism.alchemyapi.io/v2/1234567"
mainnet = "${RPC_MAINNET}"
goerli = "https://eth-goerli.alchemyapi.io/v2/${GOERLI_API_KEY}"

Etherscan API Key settings

The etherscan value accepts a list of alias = "{key = "", url? ="", chain?= """""}" items.

the key attribute is always required and should contain the actual API key for that chain or an env var that holds the key in the form ${ENV_VAR} The chain attribute is optional if the alias is the already the chain name, such as in mainnet = { key = "${ETHERSCAN_MAINNET_KEY}"} The optional url attribute can be used to explicitly set the Etherscan API url, this is the recommended setting for chains not natively supported by name.

mainnet = { key = "${ETHERSCAN_MAINNET_KEY}" }
mainnet2 = { key = "ABCDEFG", chain = "mainnet" }
optimism = { key = "1234576" }
unknownchain = { key = "ABCDEFG", url = "https://<etherscan-api-url-for-that-chain>" }
Additional Model Checker settings

Solidity's built-in model checker is an opt-in module that can be enabled via the ModelChecker object.

See Compiler Input Description settings.modelChecker and the model checker's options.

The module is available in solc release binaries for OSX and Linux. The latter requires the z3 library version [4.8.8, 4.8.14] to be installed in the system (SO version 4.8).

Similarly to the optimizer settings above, the model_checker settings must be prefixed with the profile they correspond to: [profile.default.model_checker] belongs to the [profile.default] profile.

contracts = { 'src/Contract.sol' = [ 'Contract' ] }
engine = 'chc'
timeout = 10000
targets = [ 'assert' ]

The fields above are recommended when using the model checker. Setting which contract should be verified is extremely important, otherwise all available contracts will be verified which can consume a lot of time. The recommended engine is chc, but bmc and all (runs both) are also accepted. It is also important to set a proper timeout (given in milliseconds), since the default time given to the underlying solvers may not be enough. If no verification targets are given, only assertions will be checked.

The model checker will run when forge build is invoked, and will show findings as warnings if any.

Environment Variables

Foundry's tools read all environment variable names prefixed with FOUNDRY_ using the string after the _ as the name of a configuration value as the value of the parameter as the value itself. But the corresponding dapptools config vars are also supported, this means that FOUNDRY_SRC and DAPP_SRC are equivalent.

Some exceptions to the above are explicitly ignored due to security concerns.

Environment variables take precedence over values in foundry.toml. Values are parsed as loose form of TOML syntax. Consider the following examples:


~718K SLoC