Scala Compiler Options

This doc page is specific to features shipped in Scala 2, which have either been removed in Scala 3 or replaced by an alternative. Unless otherwise stated, all the code examples in this page assume you are using Scala 2.

Introduction

The Scala compiler scalac offers various compiler options, or flags, that change the compiler’s default behavior. Some options just generate more compiler output in the form of diagnostics or warnings, while others change the result of compilation.

The Scala command scala, which runs scripts or compiled code, accepts the same options as the scalac compiler, plus a few more that determine how to run a program.

Options may be specified on the command line to scalac or in the configuration of a build tool or IDE.

The Scala distribution includes a man page. If Scala is installed as a system command, that documentation may be available from man scalac.

How to use compiler options

Use compiler options with scalac

scalac [ <options> ] <source files>

Boolean flags are specified in the usual way:

scalac -Werror -Xlint Hello.scala

Options that require arguments use “colon” syntax:

scalac -Vprint:parser,typer

Options that take just a single argument accept traditional syntax:

scalac -d /tmp

Conventionally, options have a prefix -V if they show “verbose” output; -W to manage warnings; -X for extended options that modify tool behavior; -Y for private options with limited support, where Y may suggest forking behavior. Several options have historical aliases, such as -Xfatal-warnings for -Werror.

In Scala 2, default paths can be listed by running a tool in the distribution:

scala scala.tools.util.PathResolver [ <options> ]

That can help debug errors in options such as --classpath.

Use compiler options with sbt

Here is a typical configuration of the scalacOptions setting in sbt:

scalacOptions ++= Seq(          // use ++= to add to existing options
  "-encoding", "utf8",          // if an option takes an arg, supply it on the same line
  "-feature",                   // then put the next option on a new line for easy editing
  "-language:implicitConversions",
  "-language:existentials",
  "-unchecked",
  "-Werror",
  "-Xlint",                     // exploit "trailing comma" syntax so you can add an option without editing this line
)                               // for "trailing comma", the closing paren must be on the next line

The convention is always to append to the setting with ++= and to supply one option per line.

Normally the last option will have a trailing comma so that git diff is a bit cleaner when options are added.

Standard Settings

A set of standard options that are supported on the current development environment and will be supported in future releases.

-Dproperty=value

Pass -Dproperty=value directly to the runtime system.

-J<flag>

Pass flag directly to the runtime system.

-P PLUGIN:OPT1,PLUGIN:OPT2

Pass an option to a plugin

-V

Print a synopsis of verbose options.

-W

Print a synopsis of warning options.

-Werror or -Xfatal-warnings

Fail the compilation if there are any warnings.

-X

Print a synopsis of advanced options.

-Y

Print a synopsis of private options.

-bootclasspath PATH or --boot-class-path PATH

Override location of bootstrap class files.

-classpath PATH or -cp PATH or --class-path PATH

Specify where to find user class files.

Default: .

-d DIRECTORY|JAR

destination for generated classfiles.

Default: .

-dependencyfile FILE or --dependency-file FILE

Set dependency tracking file.

Default: .scala_dependencies

-deprecation or --deprecation

Emit warning and location for usages of deprecated APIs.

-encoding ENCODING or --encoding ENCODING

Specify character encoding used by source files.

Default: UTF-8

-explaintypes or --explain-types

Explain type errors in more detail.

-extdirs PATH or --extension-directories PATH

Override location of installed extensions.

-feature or --feature

Emit warning and location for usages of features that should be imported explicitly.

-g:LEVEL

Set level of generated debugging info. (none,source,line,[vars],notailcalls)

Default: vars

-g:none

-g:source

-g:line

-g:vars

-g:notailcalls

-help or --help

Print a synopsis of standard options

-javabootclasspath PATH or --java-boot-class-path PATH

Override java boot classpath.

Default:

-javaextdirs PATH or --java-extension-directories PATH

Override java extdirs classpath.

-language:FEATURE1,FEATURE2 or --language:FEATURE1,FEATURE2

Enable or disable language features

-language:dynamics

Allow direct or indirect subclasses of scala.Dynamic

-language:existentials

Existential types (besides wildcard types) can be written and inferred

-language:higherKinds

Allow higher-kinded types

-language:implicitConversions

Allow definition of implicit functions called views

-language:postfixOps

Allow postfix operator notation, such as 1 to 10 toList (not recommended)

-language:reflectiveCalls

Allow reflective access to members of structural types

-language:experimental.macros

Allow macro definition (besides implementation and application)

-no-specialization or --no-specialization

Ignore @specialize annotations.

-nobootcp or --no-boot-class-path

Do not use the boot classpath for the scala jars.

-nowarn or --no-warnings

Generate no warnings.

-opt:OPTIMIZATION1,OPTIMIZATION2

Enable optimizations

-opt:unreachable-code

Eliminate unreachable code, exception handlers guarding no instructions, redundant metadata (debug information, line numbers).

-opt:simplify-jumps

Simplify branching instructions, eliminate unnecessary ones.

-opt:compact-locals

Eliminate empty slots in the sequence of local variables.

-opt:copy-propagation

Eliminate redundant local variables and unused values (including closures). Enables unreachable-code.

-opt:redundant-casts

Eliminate redundant casts using a type propagation analysis.

-opt:box-unbox

Eliminate box-unbox pairs within the same method (also tuples, xRefs, value class instances). Enables unreachable-code.

-opt:nullness-tracking

Track nullness / non-nullness of local variables and apply optimizations.

-opt:closure-invocations

Rewrite closure invocations to the implementation method.

-opt:allow-skip-core-module-init

Allow eliminating unused module loads for core modules of the standard library (e.g., Predef, ClassTag).

-opt:assume-modules-non-null

Assume loading a module never results in null (happens if the module is accessed in its super constructor).

-opt:allow-skip-class-loading

Allow optimizations that can skip or delay class loading.

-opt:inline

Inline method invocations according to -Yopt-inline-heuristics and -opt-inline-from.

-opt:l:none

Disable optimizations. Takes precedence: -opt:l:none,+box-unbox / -opt:l:none -opt:box-unbox don`t enable box-unbox.

-opt:l:default

Enable default optimizations: unreachable-code.

-opt:l:method

Enable intra-method optimizations: unreachable-code,simplify-jumps,compact-locals,copy-propagation,redundant-casts,box-unbox,nullness-tracking,closure-invocations,allow-skip-core-module-init,assume-modules-non-null,allow-skip-class-loading.

-opt:l:inline

Enable cross-method optimizations (note: inlining requires -opt-inline-from): l:method,inline.

-opt-inline-from PATTERNS1,PATTERNS2

Patterns for classfile names from which to allow inlining, help for details.

-opt-warnings:WARNING1,WARNING2

Enable optimizer warnings

-opt-warnings:none

No optimizer warnings.

-opt-warnings:at-inline-failed-summary

One-line summary if there were @inline method calls that could not be inlined.

-opt-warnings:at-inline-failed

A detailed warning for each @inline method call that could not be inlined.

-opt-warnings:any-inline-failed

A detailed warning for every callsite that was chosen for inlining by the heuristics, but could not be inlined.

-opt-warnings:no-inline-mixed

In mixed compilation, warn at callsites methods defined in java sources (the inlining decision cannot be made without bytecode).

-opt-warnings:no-inline-missing-bytecode

Warn if an inlining decision cannot be made because a the bytecode of a class or member cannot be found on the compilation classpath.

-opt-warnings:no-inline-missing-attribute

Warn if an inlining decision cannot be made because a Scala classfile does not have a ScalaInlineInfo attribute.

-optimize or -optimise

Enables optimizations.

-print or --print

Print program with Scala-specific features removed.

-release RELEASE or --release RELEASE

Compile for a specific version of the Java platform. Supported targets: 6, 7, 8, 9

-sourcepath PATH or --source-path PATH

Specify location(s) of source files.

-target:TARGET or --target:TARGET

Target platform for object files. ([8],9,10,11,12)

Default: 8

-target:8

-target:9

-target:10

-target:11

-target:12

-toolcp PATH or --tool-class-path PATH

Add to the runner classpath.

-unchecked or --unchecked

Enable additional warnings where generated code depends on assumptions.

-uniqid or --unique-id

Uniquely tag all identifiers in debugging output.

-usejavacp or --use-java-class-path

Utilize the java.class.path in classpath resolution.

-usemanifestcp or --use-manifest-class-path

Utilize the manifest in classpath resolution.

-verbose or --verbose

Output messages about what the compiler is doing.

-version or --version

Print product version and exit.

@<file>

A text file containing compiler arguments (options and source files)

Advanced Settings

-Xcheckinit

Wrap field accessors to throw an exception on uninitialized access.

-Xdev

Indicates user is a developer - issue warnings about anything which seems amiss

-Xdisable-assertions

Generate no assertions or assumptions.

-Xelide-below ARG

Calls to @elidable methods are omitted if method priority is lower than argument

Default: -2147483648

-Xexperimental

Former graveyard for language-forking extensions.

-Xfuture

Replaced by -Xsource.

-Xgenerate-phase-graph FILE

Generate the phase graphs (outputs .dot files) to fileX.dot.

-Xlint:WARNING1,WARNING2

Enable recommended warnings

-Xlint:adapted-args

Warn if an argument list is modified to match the receiver.

-Xlint:nullary-unit

Warn when nullary methods return Unit.

-Xlint:inaccessible

Warn about inaccessible types in method signatures.

-Xlint:nullary-override

Warn when non-nullary def f() overrides nullary def f.

-Xlint:infer-any

Warn when a type argument is inferred to be Any.

-Xlint:missing-interpolator

A string literal appears to be missing an interpolator id.

-Xlint:doc-detached

A Scaladoc comment appears to be detached from its element.

-Xlint:private-shadow

A private field (or class parameter) shadows a superclass field.

-Xlint:type-parameter-shadow

A local type parameter shadows a type already in scope.

-Xlint:poly-implicit-overload

Parameterized overloaded implicit methods are not visible as view bounds.

-Xlint:option-implicit

Option.apply used implicit view.

-Xlint:delayedinit-select

Selecting member of DelayedInit.

-Xlint:package-object-classes

Class or object defined in package object.

-Xlint:stars-align

Pattern sequence wildcard must align with sequence component.

-Xlint:constant

Evaluation of a constant arithmetic expression results in an error.

-Xlint:unused

Enable -Wunused:imports,privates,locals,implicits.

-Xlint:nonlocal-return

A return statement used an exception for flow control.

-Xlint:implicit-not-found

Check @implicitNotFound and @implicitAmbiguous messages.

-Xlint:serial

@SerialVersionUID on traits and non-serializable classes.

-Xlint:valpattern

Enable pattern checks in val definitions.

-Xlint:eta-zero

Warn on eta-expansion (rather than auto-application) of zero-ary method.

-Xlint:eta-sam

Warn on eta-expansion to meet a Java-defined functional interface that is not explicitly annotated with @FunctionalInterface.

-Xlint:deprecation

Enable linted deprecations.

-Xmacro-settings OPTION1,OPTION2

Custom settings for macros.

-Xmain-class PATH

Class for manifest’s Main-Class entry (only useful with -d jar)

-Xmaxerrs ARG

Maximum errors to print

Default: 100

-Xmaxwarns ARG

Maximum warnings to print

Default: 100

-Xmigration VERSION

Warn about constructs whose behavior may have changed since version.

Default: none

-Xmixin-force-forwarders:MODE

Generate forwarder methods in classes inhering concrete methods from traits. Default: true, help to list choices.

Default: true

-Xmixin-force-forwarders:true

Always generate mixin forwarders.

-Xmixin-force-forwarders:junit

Generate mixin forwarders for JUnit-annotated methods (JUnit 4 does not support default methods).

-Xmixin-force-forwarders:false

Only generate mixin forwarders required for program correctness.

-Xno-forwarders

Do not generate static forwarders in mirror classes.

-Xno-patmat-analysis

Don’t perform exhaustivity/unreachability analysis. Also, ignore @switch annotation.

-Xnojline

Do not use JLine for editing.

-Xplugin PATHS1,PATHS2

Load a plugin from each classpath.

-Xplugin-disable PLUGIN1,PLUGIN2

Disable plugins by name.

-Xplugin-list

Print a synopsis of loaded plugins.

-Xplugin-require PLUGIN1,PLUGIN2

Abort if a named plugin is not loaded.

-Xpluginsdir PATH

Path to search for plugin archives.

Default:

-Xprompt

Display a prompt after each error (debugging option).

-Xreporter CLASSNAME

Specify a custom reporter for compiler messages.

Default: scala.tools.nsc.reporters.ConsoleReporter

-Xresident

Compiler stays resident: read source filenames from standard input.

-Xscript OBJECT

Treat the source file as a script and wrap it in a main method.

-Xsource VERSION

Treat compiler input as Scala source for the specified version, see scala/bug#8126.

Default: 2.13.0

-Xsource-reader CLASSNAME

Specify a custom method for reading source files.

-Xverify

Verify generic signatures in generated bytecode.

-Xxml:PROPERTY1,PROPERTY2

Configure XML parsing.

-Xxml:coalescing

Convert PCData to Text and coalesce sibling nodes

Verbose Settings

-Vbrowse ARG or -Ybrowse ARG

Browse the abstract syntax tree after phases

-Vclasspath or -Ylog-classpath

Output information about what classpath is being applied.

-Vdebug or -Ydebug

Increase the quantity of debugging output.

-Vdoc or -Ydoc-debug

Trace scaladoc activity.

-Vfree-terms or -Xlog-free-terms

Print a message when reification creates a free term.

-Vfree-types or -Xlog-free-types

Print a message when reification resorts to generating a free type.

-Vhot-statistics or -Yhot-statistics

Enable -Vstatistics to also print hot statistics.

-Vide or -Yide-debug

Generate, validate and output trees using the interactive compiler.

-Vimplicit-conversions or -Xlog-implicit-conversions

Print a message whenever an implicit conversion is inserted.

-Vimplicits or -Xlog-implicits

Print dependent missing implicits.

-Vimplicits-verbose-tree

Display all intermediate implicits in a chain.

-Vimplicits-max-refined ARG

max chars for printing refined types, abbreviate to F {...}

Default: 0

-Vtype-diffs

Print found/required error messages as colored diffs.

-Vinline PACKAGE/CLASS.METHOD or -Yopt-log-inline PACKAGE/CLASS.METHOD

Print a summary of inliner activity; _ to print all, prefix match to select.

-Vissue or -Yissue-debug

Print stack traces when a context issues an error.

-Vlog ARG or -Ylog ARG

Log operations during phases

-Vmacro or -Ymacro-debug-verbose

Trace macro activities: compilation, generation of synthetics, classloading, expansion, exceptions.

-Vmacro-lite or -Ymacro-debug-lite

Trace macro activities with less output.

-Vopt PACKAGE/CLASS.METHOD or -Yopt-trace PACKAGE/CLASS.METHOD

Trace the optimizer progress for methods; _ to print all, prefix match to select.

-Vpatmat or -Ypatmat-debug

Trace pattern matching translation.

-Vphases or -Xshow-phases

Print a synopsis of compiler phases.

-Vpos or -Ypos-debug

Trace position validation.

-Vprint ARG or -Xprint ARG

Print out program after phases

-Vprint-args FILE or -Xprint-args FILE

Print all compiler arguments to the specified location. Use - to echo to the reporter.

Default: -

-Vprint-pos or -Xprint-pos

Print tree positions, as offsets.

-Vprint-types or -Xprint-types

Print tree types (debugging option).

-Vquasiquote or -Yquasiquote-debug

Trace quasiquotations.

-Vreflective-calls or -Xlog-reflective-calls

Print a message when a reflective method call is generated

-Vreify or -Yreify-debug

Trace reification.

-Vshow ARG or -Yshow ARG

(Requires -Xshow-class or -Xshow-object) Show after phases

-Vshow-class CLASS or -Xshow-class CLASS

Show internal representation of class.

-Vshow-member-pos OUTPUT STYLE or -Yshow-member-pos OUTPUT STYLE

Show start and end positions of members (implies -Yrangepos)

-Vshow-object OBJECT or -Xshow-object OBJECT

Show internal representation of object.

-Vshow-symkinds or -Yshow-symkinds

Print abbreviated symbol kinds next to symbol names.

-Vshow-symowners or -Yshow-symowners

Print owner identifiers next to symbol names.

-Vstatistics ARG or -Ystatistics ARG

Print compiler statistics for specific phases phases (default: parser,typer,patmat,erasure,cleanup,jvm)

Default: parser,typer,patmat,erasure,cleanup,jvm

-Vsymbols or -Yshow-syms

Print the AST symbol hierarchy after each phase.

-Vtyper or -Ytyper-debug

Trace type assignments.

Private Settings

-Ybackend-parallelism ARG

maximum worker threads for backend

Default: 1
Min: 1
Max: 16

-Ybackend-worker-queue ARG

backend threads worker queue size

Default: 0
Min: 0
Max: 1000

-Ybreak-cycles

Attempt to break cycles encountered during typing

-Ycache-macro-class-loader:POLICY

Policy for caching class loaders for macros that are dynamically loaded. Default: none, help to list choices.

Default: none

-Ycache-macro-class-loader:none

Don’t cache class loader

-Ycache-macro-class-loader:last-modified

Cache class loader, using file last-modified time to invalidate

-Ycache-macro-class-loader:always

Cache class loader with no invalidation

-Ycache-plugin-class-loader:POLICY

Policy for caching class loaders for compiler plugins that are dynamically loaded. Default: none, help to list choices.

Default: none

-Ycache-plugin-class-loader:none

Don’t cache class loader

-Ycache-plugin-class-loader:last-modified

Cache class loader, using file last-modified time to invalidate

-Ycache-plugin-class-loader:always

Cache class loader with no invalidation

-Ycheck ARG

Check the tree at the end of phases

-Ycompact-trees

Use compact tree printer when displaying trees.

-Ydelambdafy:STRATEGY

Strategy used for translating lambdas into JVM code. (inline,[method])

Default: method

-Ydelambdafy:inline

-Ydelambdafy:method

-Ydump-classes DIR

Dump the generated bytecode to .class files (useful for reflective compilation that utilizes in-memory classloaders).

-Ygen-asmp DIR

Generate a parallel output directory of .asmp files (ie ASM Textifier output).

-Yimports IMPORT1,IMPORT2

Custom root imports, default is java.lang,scala,scala.Predef.

-Yjar-compression-level ARG

compression level to use when writing jar files

Default: -1
Min: -1
Max: 9

-Ymacro-annotations

Enable support for macro annotations, formerly in macro paradise.

-Ymacro-classpath PATH

The classpath used to reflectively load macro implementations, default is the compilation classpath.

-Ymacro-expand:POLICY

Control expansion of macros, useful for scaladoc and presentation compiler. ([normal],none,discard)

Default: normal

-Ymacro-expand:normal

-Ymacro-expand:none

-Ymacro-expand:discard

-Ymacro-global-fresh-names

Should fresh names in macros be unique across all compilation units

-Yno-completion

Disable tab-completion in the REPL.

-Yno-flat-classpath-cache or -YdisableFlatCpCaching

Do not cache flat classpath representation of classpath elements from jars across compiler instances.

-Yno-generic-signatures

Suppress generation of generic signatures for Java.

-Yno-imports

Compile without importing scala., java.lang., or Predef.

-Yno-predef

Compile without importing Predef.

-Yopt-inline-heuristics:STRATEGY

Set the heuristics for inlining decisions. (at-inline-annotated,everything,[default])

Default: default

-Yopt-inline-heuristics:at-inline-annotated

-Yopt-inline-heuristics:everything

-Yopt-inline-heuristics:default

-Ypatmat-exhaust-depth ARG

off

Default: 20
Min: 10
Max: 2147483647

-Yprint-trees:STYLE

How to print trees when -Vprint is enabled. ([text],compact,format,text+format)

Default: text

-Yprint-trees:text

-Yprint-trees:compact

-Yprint-trees:format

-Yprint-trees:text+format

-Yprofile-destination FILE

Profiling output - specify a file or - for console.

-Yprofile-enabled

Enable profiling.

-Yprofile-external-tool ARG

Enable profiling for a phase using an external tool hook. Generally only useful for a single phase phases (default: typer)

Default: typer

-Yprofile-run-gc ARG

Run a GC between phases - this allows heap size to be accurate at the expense of more time. Specify a list of phases, or all phases (default: _)

Default: _

-Yprofile-trace FILE

Capture trace of compilation in Chrome Trace format

Default: profile.trace

-Yrangepos

Use range positions for syntax trees.

-Yrecursion ARG

Set recursion depth used when locking symbols.

Default: 0
Min: 0
Max: 2147483647

-Yreify-copypaste

Dump the reified trees in copypasteable representation.

-Yrepl-class-based

Use classes to wrap REPL snippets instead of objects

-Yrepl-outdir PATH

Write repl-generated classfiles to given output directory (use “” to generate a temporary dir)

-Yresolve-term-conflict:STRATEGY

Resolve term conflicts. (package,object,[error])

Default: error

-Yresolve-term-conflict:package

-Yresolve-term-conflict:object

-Yresolve-term-conflict:error

-Yscriptrunner CLASSNAME

Specify a scala.tools.nsc.ScriptRunner (default, resident, shutdown, or a class name).

Default: default

-Yskip ARG

Skip phases

-Ystop-after ARG or -stop ARG

Stop after phases

-Ystop-before ARG

Stop before phases

-Yvalidate-pos ARG

Validate positions after the given phases (implies -Yrangepos) phases

Warning Settings

-Wdead-code or -Ywarn-dead-code

Warn when dead code is identified.

-Wextra-implicit or -Ywarn-extra-implicit

Warn when more than one implicit parameter section is defined.

-Wmacros:MODE or -Ywarn-macros:MODE

Enable lint warnings on macro expansions. Default: before, help to list choices.

Default: before

-Wmacros:none

Do not inspect expansions or their original trees when generating unused symbol warnings.

-Wmacros:before

Only inspect unexpanded user-written code for unused symbols.

-Wmacros:after

Only inspect expanded trees when generating unused symbol warnings.

-Wmacros:both

Inspect both user-written code and expanded trees when generating unused symbol warnings.

-Wnumeric-widen or -Ywarn-numeric-widen

Warn when numerics are widened.

-Woctal-literal or -Ywarn-octal-literal

Warn on obsolete octal syntax.

-Wself-implicit or -Ywarn-self-implicit

Warn when an implicit resolves to an enclosing self-definition.

-Wunused:WARNING1,WARNING2 or -Ywarn-unused:WARNING1,WARNING2

Enable or disable specific unused warnings

-Wunused:imports

Warn if an import selector is not referenced.

-Wunused:patvars

Warn if a variable bound in a pattern is unused.

-Wunused:privates

Warn if a private member is unused.

-Wunused:locals

Warn if a local definition is unused.

-Wunused:explicits

Warn if an explicit parameter is unused.

-Wunused:implicits

Warn if an implicit parameter is unused.

-Wunused:params

Enable -Wunused:explicits,implicits.

-Wunused:linted

-Xlint:unused.

-Wvalue-discard or -Ywarn-value-discard

Warn when non-Unit expression results are unused.

-Xlint:WARNING1,WARNING2

Enable recommended warnings

-Xlint:adapted-args

Warn if an argument list is modified to match the receiver.

-Xlint:nullary-unit

Warn when nullary methods return Unit.

-Xlint:inaccessible

Warn about inaccessible types in method signatures.

-Xlint:nullary-override

Warn when non-nullary def f() overrides nullary def f.

-Xlint:infer-any

Warn when a type argument is inferred to be Any.

-Xlint:missing-interpolator

A string literal appears to be missing an interpolator id.

-Xlint:doc-detached

A Scaladoc comment appears to be detached from its element.

-Xlint:private-shadow

A private field (or class parameter) shadows a superclass field.

-Xlint:type-parameter-shadow

A local type parameter shadows a type already in scope.

-Xlint:poly-implicit-overload

Parameterized overloaded implicit methods are not visible as view bounds.

-Xlint:option-implicit

Option.apply used implicit view.

-Xlint:delayedinit-select

Selecting member of DelayedInit.

-Xlint:package-object-classes

Class or object defined in package object.

-Xlint:stars-align

Pattern sequence wildcard must align with sequence component.

-Xlint:constant

Evaluation of a constant arithmetic expression results in an error.

-Xlint:unused

Enable -Wunused:imports,privates,locals,implicits.

-Xlint:nonlocal-return

A return statement used an exception for flow control.

-Xlint:implicit-not-found

Check @implicitNotFound and @implicitAmbiguous messages.

-Xlint:serial

@SerialVersionUID on traits and non-serializable classes.

-Xlint:valpattern

Enable pattern checks in val definitions.

-Xlint:eta-zero

Warn on eta-expansion (rather than auto-application) of zero-ary method.

-Xlint:eta-sam

Warn on eta-expansion to meet a Java-defined functional interface that is not explicitly annotated with @FunctionalInterface.

-Xlint:deprecation

Enable linted deprecations.

IDE-specific Settings

-Ypresentation-any-thread

Allow use of the presentation compiler from any thread

-Ypresentation-debug

Enable debugging output for the presentation compiler.

-Ypresentation-delay ARG

Wait number of ms after typing before starting typechecking

Default: 0
Min: 0
Max: 999

-Ypresentation-log FILE

Log presentation compiler events into file

-Ypresentation-replay FILE

Replay presentation compiler events from file

-Ypresentation-strict

Do not report type errors in sources with syntax errors.

-Ypresentation-verbose

Print information about presentation compiler tasks.

Targeting a version of the JVM

Applications or libraries targeting the JVM may wish to specify a target version.

The -release option specifies the target version, such as “8” or “18”.

Like the option for javac, it allows building against an earlier version of the JDK. It will compile against the API for that version and also output class files for that version.

The deprecated option -target does not compile against the desired API, but only specifies a target class file format.

Additional resources

Compilation Phases

parser

parse source into ASTs, perform simple desugaring

namer

resolve names, attach symbols to named trees

packageobjects

load package objects

typer

the meat and potatoes: type the trees

superaccessors

add super accessors in traits and nested classes

extmethods

add extension methods for inline classes

pickler

serialize symbol tables

refchecks

reference/override checking, translate nested objects

patmat

translate match expressions

uncurry

uncurry, translate function values to anonymous classes

fields

synthesize accessors and fields, add bitmaps for lazy vals

tailcalls

replace tail calls by jumps

specialize

@specialized-driven class and method specialization

explicitouter

this refs to outer pointers

erasure

erase types, add interfaces for traits

posterasure

clean up erased inline classes

lambdalift

move nested functions to top level

constructors

move field definitions into constructors

flatten

eliminate inner classes

mixin

mixin composition

cleanup

platform-specific cleanups, generate reflective calls

delambdafy

remove lambdas

jvm

generate JVM bytecode

terminal

the last phase during a compilation run