Scala 3 Migration Guide

New Compiler Options

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The current page only contains the options that were added in Scala 3.0.x.

Standard settings

3.0.x	description
`-color`	Colored output Default: always.
`-doc-snapshot`	Generate a documentation snapshot for the current Dotty version
`-explain`	Explain errors in more detail.
`-from-tasty`	Compile classes from tasty files. The arguments are .tasty or .jar files.
`-indent`	Together with -rewrite, remove {…} syntax when possible due to significant indentation.
`-new-syntax`	Require `then` and `do` in control expressions.
`-no-indent`	Require classical {…} syntax, indentation is not significant.
`-old-syntax`	Require `(...)` around conditions.
`-pagewidth`	Set page width Default: 80.
`-print-lines`	Show source code line numbers.
`-print-tasty`	Prints the raw tasty.
`-project`	The name of the project.
`-project-logo`	The file that contains the project’s logo (in /images).
`-project-url`	The source repository of your project.
`-project-version`	The current version of your project.
`-rewrite`	When used in conjunction with a `...-migration` source version, rewrites sources to migrate to new version.
`-siteroot`	A directory containing static files from which to generate documentation. Default: ./docs.
`-sourceroot`	Specify workspace root directory. Default: ..

Verbose settings

3.2.x	description
`-Vprofile`	Show metrics about sources and internal representations to estimate compile-time complexity.
`-Vprofile-sorted-by:<column-name>`	Show metrics about sources and internal representations sorted by given column name.
`-Vprofile-details N`	Like -Vprofile, but also show metrics about sources and internal representations of the N most complex methods

Advanced settings

3.0.x	description
`-Xignore-scala2-macros`	Ignore errors when compiling code that calls Scala2 macros, these will fail at runtime.
`-Ximport-suggestion-timeout`	Timeout (in ms) for searching for import suggestions when errors are reported.
`-Xmax-inlined-trees`	Maximal number of inlined trees. Default: 2000000
`-Xmax-inlines`	Maximal number of successive inlines. Default: 32.
`-Xprint-diff`	Print changed parts of the tree since last print.
`-Xprint-diff-del`	Print changed parts of the tree since last print including deleted parts.
`-Xprint-inline`	Show where inlined code comes from.
`-Xprint-suspension`	Show when code is suspended until macros are compiled.
`-Xrepl-disable-display`	Do not display definitions in REPL.
`-Xwiki-syntax`	Retains the Scala2 behavior of using Wiki Syntax in Scaladoc.

Private settings

3.0.x	description
`-Ycheck-all-patmat`	Check exhaustivity and redundancy of all pattern matching (used for testing the algorithm).
`-Ycheck-mods`	Check that symbols and their defining trees have modifiers in sync.
`-Ycheck-reentrant`	Check that compiled program does not contain vars that can be accessed from a global root.
`-Ycook-comments`	Cook the comments (type check `@usecase`, etc.)
`-Ydebug-error`	Print the stack trace when any error is caught.
`-Ydebug-flags`	Print all flags of definitions.
`-Ydebug-missing-refs`	Print a stacktrace when a required symbol is missing.
`-Ydebug-names`	Show internal representation of names.
`-Ydebug-pos`	Show full source positions including spans.
`-Ydebug-trace`	Trace core operations.
`-Ydebug-tree-with-id`	Print the stack trace when the tree with the given id is created. Default: -2147483648.
`-Ydebug-type-error`	Print the stack trace when a TypeError is caught
`-Ydetailed-stats`	Show detailed internal compiler stats (needs Stats.enabled to be set to true).
`-YdisableFlatCpCaching`	Do not cache flat classpath representation of classpath elements from jars across compiler instances.
`-Ydrop-comments`	Drop comments when scanning source files.
`-Ydump-sbt-inc`	For every compiled foo.scala, output the API representation and dependencies used for sbt incremental compilation in foo.inc, implies -Yforce-sbt-phases.
`-Yerased-terms`	Allows the use of erased terms.
`-Yexplain-lowlevel`	When explaining type errors, show types at a lower level.
`-Yexplicit-nulls`	Make reference types non-nullable. Nullable types can be expressed with unions: e.g. String\|Null.
`-Yforce-sbt-phases`	Run the phases used by sbt for incremental compilation (ExtractDependencies and ExtractAPI) even if the compiler is ran outside of sbt, for debugging.
`-Yfrom-tasty-ignore-list`	List of `tasty` files in jar files that will not be loaded when using -from-tasty
`-Yindent-colons`	Allow colons at ends-of-lines to start indentation blocks.
`-Yinstrument`	Add instrumentation code that counts allocations and closure creations.
`-Yinstrument-defs`	Add instrumentation code that counts method calls; needs -Yinstrument to be set, too.
`-Yno-decode-stacktraces`	how raw StackOverflow stacktraces, instead of decoding them into triggering operations.
`-Yno-deep-subtypes`	Throw an exception on deep subtyping call stacks.
`-Yno-double-bindings`	Assert no namedtype is bound twice (should be enabled only if program is error-free).
`-Yno-kind-polymorphism`	Disable kind polymorphism.
`-Yno-patmat-opt`	Disable all pattern matching optimizations.
`-Yplain-printer`	Pretty-print using a plain printer.
`-Yprint-debug`	When printing trees, print some extra information useful for debugging.
`-Yprint-debug-owners`	When printing trees, print owners of definitions.
`-Yprint-pos`	Show tree positions.
`-Yprint-pos-syms`	Show symbol definitions positions.
`-Yprint-syms`	When printing trees print info in symbols instead of corresponding info in trees.
`-Yrequire-targetName`	Warn if an operator is defined without a @targetName annotation
`-Yretain-trees`	Retain trees for top-level classes, accessible from ClassSymbol#tree
`-Yscala2-unpickler`	Control where we may get Scala 2 symbols from. This is either “always”, “never”, or a classpath. Default: always.
`-Yshow-print-errors`	Don’t suppress exceptions thrown during tree printing.
`-Yshow-suppressed-errors`	Also show follow-on errors and warnings that are normally suppressed.
`-Yshow-tree-ids`	Uniquely tag all tree nodes in debugging output.
`-Yshow-var-bounds`	Print type variables with their bounds.
`-Ytest-pickler`	Self-test for pickling functionality; should be used with -Ystop-after:pickler.
`-Yunsound-match-types`	Use unsound match type reduction algorithm.

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New Compiler Options

Standard settings

Verbose settings

Advanced settings

Private settings

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