:latest-release: 0.6.0
ifdef::env-github[] :caution-caption: :construction: :important-caption: :exclamation: :warning-caption: :warning: :tip-caption: :bulb: :note-caption: :notebook: endif::[]
IMPORTANT: This rule is included in Scalafix as https://github.com/scalacenter/scalafix/blob/v0.11.0/docs/rules/OrganizeImports.md[a built-in rule] since https://github.com/scalacenter/scalafix/releases/tag/v0.11.0[Scalafix v0.11.0]. Please refer to the https://github.com/scalacenter/scalafix/[Scalafix GitHub repository] for bug reports and feature requests.
= OrganizeImports :icons: font :sectnums: :toc-placement!: :toc-title: :toc: :toclevels: 2
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toc::[]
OrganizeImports
is a CI-friendly https://scalacenter.github.io/scalafix[Scalafix] semantic rule that helps you organize Scala import statements.
https://scalameta.org/metals/[Metals], the Scala language server, also uses OrganizeImports
to power its "organize imports" code action starting from version https://scalameta.org/metals/blog/2020/11/10/lithium.html#organize-imports-code-action[v0.9.5].
image:https://i.imgur.com/8YBdjjC.gif[]
== Getting started
=== sbt
Please refer to https://scalacenter.github.io/scalafix/docs/users/installation.html[the Scalafix documentation] for how to install Scalafix and invoking it in your sbt build.
To try this rule in the sbt console without adding this rule to your sbt build:
To include this rule in your sbt build:
=== Mill
You can also include this rule in your http://www.lihaoyi.com/mill/[Mill] build using https://github.com/joan38/mill-scalafix[mill-scalafix]:
=== For IntelliJ Scala plugin users
OrganizeImports
allows you to specify a preset style via the <<preset, preset
option>>. To make it easier to add OrganizeImports
into existing Scala projects built using the IntelliJ Scala plugin, OrganizeImports
provides a preset style compatible with the default configuration of the IntelliJ Scala import optimizer. Please check the <<intellij-2020-3, INTELLIJ_2020_3
>> preset style for more details.
=== Source formatting tools
The OrganizeImports
rule respects source-formatting tools like https://scalameta.org/scalafmt/[Scalafmt]. If an import statement is already organized according to the configuration, its original source level format is preserved. Therefore, in an sbt project, if you run the following command sequence:
Assuming that the first two commands run successfully, the last scalafixAll --check
command should not fail even if some import statements are reformatted by the scalafmtAll
command.
However, you should make sure that the source-formatting tools you use do not rewrite import statements in ways that conflict with OrganizeImports
. For example, when using Scalafmt together with OrganizeImports
, the ExpandImportSelectors
, SortImports
, and AsciiSortImports
rewriting rules should not be used.
=== Scala 3
Available since v0.6.0.
Running the rule on source files compiled with Scala 3 is still experimental.
Known limitations:
. You must use Scalafix 0.9.28 or later
. The <<removeUnused, removeUnused
>> option must be explicitly set to false
- the rule currently doesn't remove unused imports as it's currently not supported by the compiler.
. Usage of http://dotty.epfl.ch/docs/reference/dropped-features/package-objects.html[deprecated package objects] may result in incorrect imports
. The <<groupExplicitlyImportedImplicitsSeparately, groupExplicitlyImportedImplicitsSeparately>> option has no effect
== Configuration
=== Default Configuration values
Please do NOT use the Scalafix built-in https://scalacenter.github.io/scalafix/docs/rules/RemoveUnused.html[`RemoveUnused.imports] together with
OrganizeImportsto remove unused imports. You may end up with broken code! It is still safe to use
RemoveUnused` to remove unused private members or local definitions, though.
Scalafix rewrites source files by applying patches generated by invoked rules. Each rule generates a patch based on the original text of the source files. When two patches generated by different rules conflict with each other, Scalafix is not able to reconcile the conflicts, and may produce broken code. It is very likely to happen when RemoveUnused
and OrganizeImports
are used together, since both rules rewrite import statements.
OrganizeImports
already removes unused imports for you (see the <<removeUnused, removeUnused
>> option). It locates unused imports via compilation diagnostics, which is exactly how RemoveUnused
does it. This mechanism works well in most cases, unless there are new unused imports generated while organizing imports, which is possible when the <<expandRelative, expandRelative
>> option is set to true. For now, the only reliable workaround for this edge case is to run Scalafix with OrganizeImports
twice.[[blankLines]]
=== blankLines
Available since v0.5.0-alpha.1.
Configures whether blank lines between adjacent import groups are automatically or manually inserted. This option is used together with the <<blank-line-marker, ---
blank line markers>>.
==== Value type
Enum: Auto | Manual
Auto:: A blank line is automatically inserted between adjacent import groups. All blank line markers (---
) configured in the <<groups, groups
option>> are ignored.
Manual:: A blank line is inserted at all the positions where blank line markers appear in the <<groups, groups
option>>.
The following two configurations are equivalent:
OrganizeImports { blankLines = Auto groups = [ "re:javax?\." "scala." "*" ] }
==== Default value
Auto
==== Examples
Auto
::
+Configuration:
Before:
After:
import java.time.Clock import javax.annotation.Generated
import scala.collection.JavaConverters._ import scala.concurrent.ExecutionContext
--
Manual
::
+Configuration:
Before:
After:
import java.time.Clock import javax.annotation.Generated import scala.collection.JavaConverters._ import scala.concurrent.ExecutionContext
--
[[coalesceToWildcardImportThreshold]]
=== coalesceToWildcardImportThreshold
When the number of imported names exceeds a certain threshold, coalesce them into a wildcard import. Renames and unimports are left untouched.
Having this feature in OrganizeImports
is mostly for feature parity with the IntelliJ IDEA Scala import optimizer, but coalescing grouped import selectors into a wildcard import may introduce compilation errors!
Here is an example to illustrate the risk. The following snippet compiles successfully:
import scala.collection.immutable._ import scala.collection.mutable.{ArrayBuffer, Map, Set}
The type of Example.m
above is not ambiguous because the mutable Map
explicitly imported in the second import takes higher precedence than the immutable Map
imported via wildcard in the first import.
import scala.collection.immutable. import scala.collection.mutable.
Example.m
becomes ambiguous now since both the mutable and immutable Map
are imported via a wildcard and have the same precedence.==== Value type
Integer. Not setting it or setting it to null
disables this feature.
==== Default value
null
==== Examples
Configuration:
Before:
After:
[[expandRelative]]
=== expandRelative
Expand relative imports into fully-qualified one.
Expanding relative imports may introduce new unused imports. For instance, relative imports in the following snippet
are expanded into
If neither scala.util
nor scala.util.control
is referenced anywhere after the expansion, they become unused imports.
removeUnused
to true
. Please refer to the <<removeUnused, removeUnused
>> option for more details.==== Value type
Boolean
==== Default value
false
==== Examples
Configuration:
Before:
After:
import java.time.Clock import javax.annotation.Generated
import scala.collection.JavaConverters._ import scala.concurrent.ExecutionContext import scala.util import scala.util.control import scala.util.control.NonFatal
[[groupExplicitlyImportedImplicitsSeparately]]
=== groupExplicitlyImportedImplicitsSeparately
This option provides a workaround to a subtle and rarely seen correctness issue related to explicitly imported implicit names.
The following snippet helps illustrate the problem:
package a
import c._ import b.i
object b { implicit def i: Int = 1 } object c { implicit def i: Int = 2 }
The above snippet compiles successfully and outputs 1
, because the explicitly imported implicit value b.i
overrides c.i
, which is made available via a wildcard import. However, if we reorder the two imports into:
The Scala compiler starts complaining:
This behavior could be due to a Scala compiler bug since https://scala-lang.org/files/archive/spec/2.13/02-identifiers-names-and-scopes.html[the Scala language specification] requires that explicitly imported names should have higher precedence than names made available via a wildcard.
Unfortunately, Scalafix is not able to surgically identify conflicting implicit values behind a wildcard import. In order to guarantee correctness in all cases, when the groupExplicitlyImportedImplicitsSeparately
option is set to true
, all explicitly imported implicit names are moved into the trailing order-preserving import group together with relative imports, if any (see the <<trailing-order-preserving-import-group, trailing order-preserving import group>> section for more details).
CAUTION: In general, order-sensitive imports are fragile, and can easily be broken by either human collaborators or tools (e.g., the IntelliJ IDEA Scala import optimizer does not handle this case correctly). They should be eliminated whenever possible. This option is mostly useful when you are dealing with a large trunk of legacy codebase, and you want to minimize manual intervention and guarantee correctness in all cases.
groupExplicitlyImportedImplicitsSeparately
option has currently no effect on source files compiled with Scala 3, as the https://github.com/lampepfl/dotty/issues/12766[compiler does not expose full signature information], preventing the rule to identify imported implicits.==== Value type
Boolean
==== Default value
false
This option defaults to false
due to the following reasons:
. Although setting it to true
avoids the aforementioned correctness issue, the result is unintuitive and confusing for many users since it looks like the groups
option is not respected.
+
E.g., why my scala.concurrent.ExecutionContext.Implicits.global
import is moved to a separate group even if I have a scala.
group defined in the groups
option?
==== Examples
Configuration:
Before:
After:
import scala.collection.mutable.ArrayBuffer import scala.collection.mutable.Buffer
import org.apache.spark.RDD import org.apache.spark.SparkContext
[[groupedImports]]
=== groupedImports
Configure how to handle grouped imports.
==== Value type
Enum: Explode | Merge | AggressiveMerge | Keep
Explode
:: Explode grouped imports into separate import statements.
Merge
::
+Merge imports sharing the same prefix into a single grouped import statement.
AggressiveMerge
>> option for more concise results despite a relatively low risk of introducing compilation errors.OrganizeImports
does not support cases where one name is renamed to multiple aliases within the same source file when groupedImports
is set to Merge
. (The IntelliJ IDEA Scala import optimizer does not support this either.)
Scala allows a name to be renamed to multiple aliases within a single source file, which makes merging import statements tricky. For example:
The above three imports can be merged into:
but not:
because Scala disallow a name (in this case, Double
) to appear in one import multiple times.
Here's a more complicated example:
import p.{A => A1} import p.{A => A2} import p.{A => A3}
import p.{B => B1} import p.{B => B2}
While merging these imports, we may want to "bin-pack" them to minimize the number of the result import statements:
OrganizeImports
does not support this when groupedImports
is set to Merge
to avoid the extra complexity.--
AggressiveMerge
::
+Similar to Merge
, but merges imports more aggressively and produces more concise results, despite a relatively low risk of introducing compilation errors.
The OrganizeImports
rule tries hard to guarantee correctness in all cases. This forces it to be more conservative when merging imports, and may sometimes produce suboptimal output. Here is a concrete example about correctness:
import scala.collection.immutable. import scala.collection.mutable.Map import scala.collection.mutable.
At a first glance, it seems feasible to simply drop the second import since mutable._
already covers mutble.Map
. However, similar to the example illustrated in the section about the <<coalesceToWildcardImportThreshold, coalesceToWildcardImportThreshold
option>>, the type of Example.m
above is mutable.Map
, because the mutable Map
explicitly imported in the second import takes higher precedence than the immutable Map
imported via wildcard in the first import. If we merge the last two imports naively, we'll get:
This triggers in a compilation error, because both immutable.Map
and mutable.Map
are now imported via wildcards with the same precedence. This makes the type of Example.m
ambiguous. The correct result should be:
On the other hand, the case discussed above is rarely seen in practice. A more commonly seen case is something like:
Instead of being conservative and produce a suboptimal output like:
setting groupedImports
to AggressiveMerge
produces
--
Keep
:: Leave grouped imports and imports sharing the same prefix untouched.
==== Default value
Explode
Rationale:: Despite making the import section lengthier, exploding grouped imports into separate import statements is made the default behavior because it is more friendly to version control and less likely to create annoying merge conflicts caused by trivial import changes.
==== Examples
Explode
::
+Configuration:
Before:
After:
--
Merge
::
+Configuration:
Before:
After:
--
AggressiveMerge
::
+Configuration:
Before:
After:
--
[[groups]]
=== groups
Defines import groups by prefix patterns. Only global imports are processed.
All the imports matching the same prefix pattern are gathered into the same group and sorted by the order defined by the <<importsOrder, importsOrder
>> option.
CAUTION: Comments living between imports being processed will be removed.
OrganizeImports
tries to match the longest prefix while grouping imports. For instance, the following configuration groups scala.meta.
and scala.
imports into different two groups properly:
====
No matter how the groups
option is configured, a special order-preserving import group may appear after all the configured import groups when:
. The expandRelative
option is set to false
and there are relative imports.
. The groupExplicitlyImportedImplicitsSeparately
option is set to true
and there are implicit names explicitly imported.
This special import group is necessary because the above two kinds of imports are order sensitive:
For instance, sorting the following imports in alphabetical order introduces compilation errors:
--
groupExplicitlyImportedImplicitsSeparately
>> option for more details.==== Value type
An ordered list of import prefix pattern strings. A prefix pattern can be one of the following:
A plain-text pattern:: For instance, "scala."
is a plain-text pattern that matches imports referring the scala
package. Please note that the trailing dot is necessary, otherwise you may have scalafix
and scala
imports in the same group, which is not what you want in most cases.
A regular expression pattern:: A regular expression pattern starts with re:
. For instance, "re:javax?\\."
is such a pattern that matches both the java
and the javax
packages. Please refer to the https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html[`java.util.regex.Pattern`] Javadoc page for the regular expression syntax. Note that special characters like backslashes must be escaped.
The wildcard pattern, "*"
, defines the wildcard group, which matches all fully-qualified imports not belonging to any other groups. It can be omitted when it's the last group. So the following two configurations are equivalent:
--
Available since v0.5.0-alpha.1.
A blank line marker, "---"
, defines a blank line between two adjacent import groups when <<blankLines, blankLines
>> is set to Manual
. It is ignored when blankLines
is Auto
. Leading and trailing blank line markers are always ignored. Multiple consecutive blank line markers are treated as a single one. So the following three configurations are all equivalent:
OrganizeImports { blankLines = Manual groups = [ "---" "re:javax?\." "---" "scala." "---" "---" "*" "---" ] }
OrganizeImports { blankLines = Manual groups = [ "re:javax?\." "---" "scala." "---" "*" ] }
--
==== Default value
Rationale:: This aligns with the default configuration of the IntelliJ Scala plugin version 2020.3.
==== Examples
Configuration:
Before:
After:
import java.time.Clock import javax.annotation.Generated
import scala.collection.JavaConverters._ import scala.concurrent.ExecutionContext
--
Configuration:
Before:
After:
import java.time.Clock import javax.annotation.Generated
import scala.collection.JavaConverters._ import scala.concurrent.ExecutionContext import scala.util
import sun.misc.BASE64Encoder
--
Configuration:
Before:
After:
import java.time.Clock import javax.annotation.Generated
import scala.collection.JavaConverters._ import scala.util
import sun.misc.BASE64Encoder
--
Defining import groups using regular expressions can be quite flexible. For instance, the scala.meta
package is not part of the Scala standard library, but the default groups defined in the OrganizeImports.groups
option move imports from this package into the scala.
group. The following example illustrates how to move them into the wildcard group using regular expression.
import java.time.Clock import javax.annotation.Generated
import scala.collection.JavaConverters._ import scala.concurrent.ExecutionContext
--
Configuration:
Before:
After:
import sun.misc.BASE64Encoder
--
[[importSelectorsOrder]]
=== importSelectorsOrder
Specifies the order of grouped import selectors within a single import expression.
==== Value type
Enum: Ascii | SymbolsFirst | Keep
Ascii
:: Sort import selectors by ASCII codes, equivalent to the https://scalameta.org/scalafmt/docs/configuration.html#asciisortimports[`AsciiSortImports`] rewriting rule in Scalafmt.
SymbolsFirst
:: Sort import selectors by the groups: symbols, lower-case, upper-case, equivalent to the https://scalameta.org/scalafmt/docs/configuration.html#sortimports[`SortImports`] rewriting rule in Scalafmt.
Keep
:: Keep the original order.
==== Default value
Ascii
==== Examples
Ascii
::
+Configuration:
Before:
symbol
, bar, Random}After:
symbol
, bar, ~>}--
SymbolsFirst
::
+Configuration:
Before:
symbol
, bar, ~>}After:
symbol
, bar, Random}--
[[importsOrder]]
=== importsOrder
Specifies the order of import statements within import groups defined by the <<groups, OrganizeImports.groups
>> option.
==== Value type
Enum: Ascii | SymbolsFirst | Keep
Ascii
:: Sort import statements by ASCII codes. This is the default sorting order that the IntelliJ IDEA Scala import optimizer picks ("lexicographically" option).
SymbolsFirst
:: Put wildcard imports and grouped imports with braces first, otherwise same as Ascii
. This replicates IntelliJ IDEA Scala's "scalastyle consistent" option.
Keep
:: Keep the original order.
==== Default value
Ascii
==== Examples
Ascii
::
+Configuration:
Before:
After:
--
SymbolsFirst
::
+Configuration:
Before:
After:
--
[[preset]]
=== preset
Available since v0.5.0.
Specify a preset style.
==== Value type
Enum: DEFAULT | INTELLIJ_2020_3
DEFAULT
::
+An opinionated style recommended for new projects. The OrganizeImports
rule tries its best to ensure correctness in all cases when possible. This default style aligns with this principal. In addition, by setting groupedImports
to Explode
, this style is also more friendly to version control and less likely to create annoying merge conflicts caused by trivial import changes.
--
INTELLIJ_2020_3
::
+A style that is compatible with the default configuration of the IntelliJ Scala 2020.3 import optimizer. It is mostly useful for adding OrganizeImports
to existing projects developed using the IntelliJ Scala plugin. However, the configuration of this style may introduce subtle correctness issues (so does the default configuration of the IntelliJ Scala plugin). Please see the <<coalesceToWildcardImportThreshold, coalesceToWildcardImportThreshold
option>> for more details.
--
==== Default value
DEFAULT
[[removeUnused]]
=== removeUnused
Remove unused imports.
removeUnused
option doesn't play perfectly with the expandRelative
option. Setting expandRelative
to true
might introduce new unused imports (see <<expandRelative, expandRelative
>>). These newly introduced unused imports cannot be removed by setting removeUnused
to true
. This is because unused imports are identified using Scala compilation diagnostics information, and the compilation phase happens before Scalafix rules get applied.removeUnused
option is currently not supported for source files compiled with Scala 3, as the https://docs.scala-lang.org/scala3/guides/migration/options-lookup.html#warning-settings[compiler cannot issue warnings for unused imports yet]. As a result, you must set removeUnused
to false
when running the rule on source files compiled with Scala 3.==== Value type
Boolean
==== Default value
true
==== Examples
Configuration:
Before:
import scala.collection.mutable.{Buffer, ArrayBuffer} import java.time.Clock import java.lang.{Long => JLong, Double => JDouble}
After:
import java.lang.{Long => JLong}
import scala.collection.mutable.ArrayBuffer