.flowconfig [options]
How to configure Flow's various options
The [options]
section in a .flowconfig
file can contain several key-value
pairs of the form:
[options]
keyA=valueA
keyB=valueB
Any options that are omitted will use their default values. Some options can be overridden with command line flags.
Available options
all
autoimports
babel_loose_array_spread
emoji
exact_by_default
experimental.const_params
include_warnings
lazy_mode
log.file
max_header_tokens
module.file_ext
module.ignore_non_literal_requires
module.name_mapper
module.name_mapper.extension
module.system
module.system.node.main_field
module.system.node.resolve_dirname
module.use_strict
munge_underscores
no_flowlib
react.runtime
server.max_workers
sharedmemory.dirs
sharedmemory.minimum_available
sharedmemory.hash_table_pow
sharedmemory.heap_size
sharedmemory.log_level
suppress_type
temp_dir
traces
The following options are deprecated and have been removed in the latest version of Flow:
strip_root
suppress_comment
types_first
well_formed_exports
esproposal.class_instance_fields
esproposal.class_static_fields
esproposal.decorators
esproposal.export_star_as
esproposal.optional_chaining
esproposal.nullish_coalescing
all
(boolean)
Set this to true
to check all files, not just those with @flow
.
The default value for all
is false
.
autoimports
(boolean)
≥0.143.0
When enabled, IDE autocomplete suggests the exports of other files, and the necessary import
statements are automatically inserted. A “quick fix” code action is also provided on undefined variables that suggests matching imports.
The default value for autoimports
is true
as of Flow v0.155.0.
babel_loose_array_spread
(boolean)
Set this to true
to check that array spread syntax is only used with arrays, not arbitrary iterables (such as Map
or Set
). This is useful if you transform your code with Babel in loose mode which makes this non-spec-compliant assumption at runtime.
For example:
1 2 |
|
The default value for babel_loose_array_spread
is false
.
emoji
(boolean)
Set this to true
to add emoji to the status messages that Flow
outputs when it’s busy checking your project.
The default value for emoji
is false
.
exact_by_default
(boolean)
Set this to true
to indicate that Flow should interpret object types as exact
by default. When this flag is false
, Flow has the following behavior:
1 2 3 |
|
When this flag is true
, Flow has the following behavior:
1 2 3 |
|
The default value is false
.
experimental.const_params
(boolean)
Setting this to true
makes Flow treat all function parameters as const
bindings. Reassigning a param is an error which lets Flow be less conservative
with refinements.
The default value is false
.
include_warnings
(boolean)
Setting this to true
makes Flow commands include warnings in the error output.
Warnings are hidden by default in the CLI to avoid console spew. (An IDE is a
much better interface to show warnings.)
The default value is false
.
lazy_mode
(fs|ide|watchman|none)
For more on lazy modes, see the lazy modes docs.
Setting lazy_mode
in the .flowconfig
will cause new Flow servers for that
root to use that lazy mode (or no lazy mode if set to none
). This option can
be overridden from the CLI using the --lazy-mode
flag.
The default value is none
.
log.file
(string)
The path to the log file (defaults to /tmp/flow/<escaped root path>.log
).
max_header_tokens
(integer)
Flow tries to avoid parsing non-flow files. This means Flow needs to
start lexing a file to see if it has @flow
or @noflow
in it. This option
lets you configure how much of the file Flow lexes before it decides there is
no relevant docblock.
- Neither
@flow
nor@noflow
- Parse this file with Flow syntax disallowed and do not typecheck it. - @flow - Parse this file with Flow syntax allowed and typecheck it.
- @noflow - Parse this file with Flow syntax allowed and do not typecheck it. This is meant as an escape hatch to suppress Flow in a file without having to delete all the Flow-specific syntax.
The default value of max_header_tokens
is 10.
module.file_ext
(string)
By default, Flow will look for files with the extensions .js
, .jsx
, .mjs
,
.cjs
and .json
. You can override this behavior with this option.
For example, if you do:
[options]
module.file_ext=.foo
module.file_ext=.bar
Then Flow will instead look for the file extensions .foo
and .bar
.
Note: you can specify
module.file_ext
multiple times
module.ignore_non_literal_requires
(boolean)
Set this to true
and Flow will no longer complain when you use require()
with something other than a string literal.
The default value is false
.
module.name_mapper
(regex -> string)
Specify a regular expression to match against module names, and a replacement
pattern, separated by a ->
.
For example:
module.name_mapper='^image![a-zA-Z0-9$_]+$' -> 'ImageStub'
This makes Flow treat require('image!foo.jpg')
as if it were
require('ImageStub')
.
These are OCaml regular expressions.
Use \(
and \)
(slashes required!) to create a capturing group, which you
can refer to in the replacement pattern as \1
(up to \9
).
Note: you can specify
module.name_mapper
multiple times
module.name_mapper.extension
(string -> string)
Specify a file extension to match, and a replacement module name, separated by
a ->
.
Note: This is just shorthand for
module.name_mapper='^\(.*\)\.EXTENSION$' -> 'TEMPLATE'
)
For example:
module.name_mapper.extension='css' -> '<PROJECT_ROOT>/CSSFlowStub.js.flow'
Makes Flow treat require('foo.css')
as if it were
require(PROJECT_ROOT + '/CSSFlowStub')
.
Note: You can specify
module.name_mapper.extension
multiple times for different extensions.
module.system
(node|haste)
The module system to use to resolve import
and require
.
Haste is used in React Native.
The default is node
.
module.system.node.main_field
(string)
Flow reads package.json
files for the "name"
and "main"
fields to figure
out the name of the module and which file should be used to provide that
module.
So if Flow sees this in the .flowconfig
:
[options]
module.system.node.main_field=foo
module.system.node.main_field=bar
module.system.node.main_field=baz
and then it comes across a package.json
with
{
"name": "kittens",
"main": "main.js",
"bar": "bar.js",
"baz": "baz.js"
}
Flow will use bar.js
to provide the "kittens"
module.
If this option is unspecified, Flow will always use the "main"
field.
See this GitHub issue for the original motivation
module.system.node.resolve_dirname
(string)
By default, Flow will look in directories named node_modules
for node
modules. You can configure this behavior with this option.
For example, if you do:
[options]
module.system.node.resolve_dirname=node_modules
module.system.node.resolve_dirname=custom_node_modules
Then Flow will look in directories named node_modules
or
custom_node_modules
.
Note: you can specify
module.system.node.resolve_dirname
multiple times
module.use_strict
(boolean)
Set this to true
if you use a transpiler that adds "use strict";
to the top
of every module.
The default value is false
.
munge_underscores
(boolean)
Set this to true
to have Flow treat underscore-prefixed class properties and
methods as private. This should be used in conjunction with jstransform
’s
ES6 class transform,
which enforces the same privacy at runtime.
The default value is false
.
no_flowlib
(boolean)
Flow has builtin library definitions. Setting this to true
will tell Flow to
ignore the builtin library definitions.
The default value is false
.
react.runtime
(automatic|classic)
≥0.123.0
Set this to automatic
if you are using React’s automatic runtime in @babel/plugin-transform-react-jsx
.
Otherwise, use classic
. See the babel documentation
for details about the transform.
The default value is automatic
.
server.max_workers
(integer)
The maximum number of workers the Flow server can start. By default, the server will use all available cores.
sharedmemory.dirs
(string)
This affects Linux only.
Flow’s shared memory lives in a memory mapped file. On more modern versions of
Linux (3.17+), there is a system call memfd_create
which allows Flow to create
the file anonymously and only in memory. However, in older kernels, Flow needs
to create a file on the file system. Ideally this file lives on a memory-backed
tmpfs. This option lets you decide where that file is created.
By default this option is set to /dev/shm
and /tmp
Note: You can specify
sharedmemory.dirs
multiple times.
sharedmemory.minimum_available
(unsigned integer)
This affects Linux only.
As explained in the sharedmemory.dirs
option’s description, Flow needs to
create a file on a filesystem for older kernels. sharedmemory.dirs
specifies
a list of locations where the shared memory file can be created. For each
location, Flow will check to make sure the filesystem has enough space for the
shared memory file. If Flow will likely run out of space, it skips that location
and tries the next. This option lets you configure the minimum amount of space
needed on a filesystem for shared memory.
By default it is 536870912 (2^29 bytes, which is half a gigabyte).
sharedmemory.hash_table_pow
(unsigned integer)
The 3 largest parts of the shared memory are a dependency table, a hash table, and a heap. While the heap grows and shrinks, the two tables are allocated in full. This option lets you change the size of the hash table.
Setting this option to X means the table will support up to 2^X elements, which is 16*2^X bytes.
By default, this is set to 19 (Table size is 2^19, which is 8 megabytes)
sharedmemory.heap_size
(unsigned integer)
This option configures the maximum possible size for the shared heap. You should most likely not need to configure this, as it doesn’t really affect how much RSS Flow uses. However, if you are working on a massive codebase you might see the following error after init: “Heap init size is too close to max heap size; GC will never get triggered!” In this case, you may need to increase the size of the heap.
By default, this is set to 26843545600 (25 * 2^30 bytes, which is 25GiB)
sharedmemory.log_level
(unsigned integer)
Setting this to 1 will cause Flow to output some stats about the data that is serialized into and deserialized out of shared memory.
By default this is 0.
suppress_type
(string)
This option lets you alias any
with a given string. This is useful for
explaining why you’re using any
. For example, let’s say you sometimes want
to sometimes use any
to suppress an error and sometimes to mark a TODO.
Your code might look like
var myString: any = 1 + 1;
var myBoolean: any = 1 + 1;
If you add the following to your configuration:
[options]
suppress_type=$FlowFixMe
suppress_type=$FlowTODO
You can update your code to the more readable:
var myString: $FlowFixMe = 1 + 1;
var myBoolean: $FlowTODO = 1 + 1;
Note: You can specify
suppress_type
multiple times.
temp_dir
(string)
Tell Flow which directory to use as a temp directory. Can be overridden with the
command line flag --temp-dir
.
The default value is /tmp/flow
.
traces
(integer)
Enables traces on all error output (showing additional details about the flow of types through the system), to the depth specified. This can be very expensive, so is disabled by default.
strip_root
(boolean)
≤0.48
Obsolete. Set this to true
to always strip the root directory from file paths
in error messages when using --json
, --from emacs
, and --from vim
.
Do not use this option. Instead, pass the command line flag --strip-root
.
By default this is false
.
suppress_comment
(regex)
≤0.126
Defines a magical comment that suppresses any Flow errors on the following line. For example:
suppress_comment= \\(.\\|\n\\)*\\$FlowFixMe
will match a comment like this:
// $FlowFixMe: suppressing this error until we can refactor
var x : string = 123;
and suppress the error. If there is no error on the next line (the suppression is unnecessary), an “Unused suppression” warning will be shown instead.
If no suppression comments are specified in your config, Flow will apply one
default: // $FlowFixMe
.
Note: You can specify
suppress_comment
multiple times. If you do define anysuppress_comment
s, the built-in$FlowFixMe
suppression will be erased in favor of the regexps you specify. If you wish to use$FlowFixMe
with some additional custom suppression comments, you must manually specify\\(.\\|\n\\)*\\$FlowFixMe
in your custom list of suppressions.
Note: In version v0.127.0, the option to specify the suppression comment syntax was removed.
$FlowFixMe
,$FlowIssue
,$FlowExpectedError
, and$FlowIgnore
became the only standard suppressions.
types_first
(boolean)
≥0.125.0 ≤0.142
For more on types-first mode, see the types-first docs.
Flow builds intermediate artifacts to represent signatures of modules as they are
checked. If this option is set to false
, then these artifacts are built using
inferred type information. If this option is set to true
, then they are built
using type annotations at module boundaries.
The default value for types_first
is true
(as of version 0.134).
well_formed_exports
(boolean)
≥0.125.0 ≤0.142
Enforce the following restrictions on file exports:
- Statements manipulating
module.exports
and theexports
alias may only appear as top-level statements. - Parts of the source that are visible from a file’s exports need to be annotated
unless their type can be trivially inferred (e.g. the exported expression is a
numeric literal). This is a requirement for types-first mode to function properly.
Failure to properly annotate exports raise
signature-verification-failure
s.
This option is set to true
by default, since it is implied by types_first
,
but the option is useful on its own when upgrading a project from classic mode to
types-first mode.
well_formed_exports.includes
(string)
≥0.128.0 ≤0.142
Limit the scope of the well_formed_exports
requirement to a specific directory
of this project. For example
well_formed_exports=true
well_formed_exports.includes=<PROJECT_ROOT>/dirA
well_formed_exports.includes=<PROJECT_ROOT>/dirB
will only report export related errors in files under dirA
and dirB
. This option
requires well_formed_exports
to be set to true
.
The purpose of this option is to help prepare a codebase for Flow types-first mode. See this section for more.
Between versions v0.125.0 and v0.127.0, this option was named well_formed_exports.whitelist
.
esproposal.class_instance_fields
(enable|ignore|warn)
≤0.148
Set this to warn
to indicate that Flow should give a warning on use of
instance class fields
per the pending spec.
You may also set this to ignore
to indicate that Flow should simply ignore
the syntax (i.e. Flow will not use this syntax to indicate the presence of a
property on instances of the class).
The default value of this option is enable
, which allows use of this proposed
syntax.
esproposal.class_static_fields
(enable|ignore|warn)
≤0.148
Set this to warn
to indicate that Flow should give a warning on use of static
class fields
per the pending spec.
You may also set this to ignore
to indicate that Flow should simply ignore
the syntax (i.e. Flow will not use this syntax to indicate the presence of a
static property on the class).
The default value of this option is enable
, which allows use of this proposed
syntax.
esproposal.decorators
(ignore|warn)
≤0.148
Set this to ignore
to indicate that Flow should ignore decorators.
The default value of this option is warn
, which gives a warning on use since
this proposal is still very early-stage.
esproposal.export_star_as
(enable|ignore|warn)
≤0.148
Set this to enable
to indicate that Flow should support the export * as
syntax from leebyron’s proposal.
You may also set this to ignore
to indicate that Flow should simply ignore
the syntax. The default value of this option is warn
, which gives a warning
on use since this proposal is still very early-stage.
esproposal.optional_chaining
(enable|ignore|warn)
≤0.148
Set this to enable
to indicate that Flow should support the use of
optional chaining
per the pending spec.
You may also set this to ignore
to indicate that Flow should simply ignore
the syntax.
The default value of this option is warn
, which gives a warning on
use since this proposal is still very early-stage.
esproposal.nullish_coalescing
(enable|ignore|warn)
≤0.148
Set this to enable
to indicate that Flow should support the use of
nullish coalescing
per the pending spec.
You may also set this to ignore
to indicate that Flow should simply ignore
the syntax.
The default value of this option is warn
, which gives a warning on
use since this proposal is still very early-stage.
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