title	description
scalafix configuration in MegaLinter	How to use scalafix (configure, ignore files, ignore errors, help & version documentations) to analyze SCALA files

scalafix

Scalafix is a refactoring and linting tool for Scala that automates code quality maintenance, enabling both one-time migrations and continuous code health enforcement.

Key Features:

Automated Refactoring: Handles day-to-day code maintenance tasks and complex migration scripts with precision
Comprehensive Linting: Reports errors for code patterns that cause production bugs or violate coding standards
Syntactic and Semantic Rules: Supports both syntax-based rules (no compilation needed) and semantic rules (requires compilation)
Built-in Rule Library: Extensive collection of rules for common Scala patterns, deprecations, and best practices
Custom Rule Development: Extensible architecture for writing project-specific rules and transformations
Configuration Flexibility: Highly configurable through .scalafix.conf files with rule-specific settings

Note: In MegaLinter, only syntactic rules are applied as there is no prior compilation or semantic database generation. Semantic options cannot be used in this context.

scalafix documentation

Version in MegaLinter: 0.14.4
Visit Official Web Site{target=_blank}
See How to configure scalafix rules{target=_blank}
- If custom .scalafix.conf config file isn't found, .scalafix.conf{target=_blank} will be used
See How to disable scalafix rules in files{target=_blank}
See Index of problems detected by scalafix{target=_blank}

{target=_blank}

Configuration in MegaLinter

Enable scalafix by adding SCALA_SCALAFIX in ENABLE_LINTERS variable
Disable scalafix by adding SCALA_SCALAFIX in DISABLE_LINTERS variable

Variable	Description	Default value
SCALA_SCALAFIX_ARGUMENTS	User custom arguments to add in linter CLI call Ex: `-s --foo "bar"`
SCALA_SCALAFIX_COMMAND_REMOVE_ARGUMENTS	User custom arguments to remove from command line before calling the linter Ex: `-s --foo "bar"`
SCALA_SCALAFIX_FILTER_REGEX_INCLUDE	Custom regex including filter Ex: `(src\|lib)`	Include every file
SCALA_SCALAFIX_FILTER_REGEX_EXCLUDE	Custom regex excluding filter Ex: `(test\|examples)`	Exclude no file
SCALA_SCALAFIX_CLI_LINT_MODE	Override default CLI lint mode - `file`: Calls the linter for each file - `project`: Call the linter from the root of the project	`file`
SCALA_SCALAFIX_FILE_EXTENSIONS	Allowed file extensions. `"*"` matches any extension, `""` matches empty extension. Empty list excludes all files Ex: `[".py", ""]`	`[".scala"]`
SCALA_SCALAFIX_FILE_NAMES_REGEX	File name regex filters. Regular expression list for filtering files by their base names using regex full match. Empty list includes all files Ex: `["Dockerfile(-.+)?", "Jenkinsfile"]`	Include every file
SCALA_SCALAFIX_PRE_COMMANDS	List of bash commands to run before the linter	None
SCALA_SCALAFIX_POST_COMMANDS	List of bash commands to run after the linter	None
SCALA_SCALAFIX_UNSECURED_ENV_VARIABLES	List of env variables explicitly not filtered before calling SCALA_SCALAFIX and its pre/post commands	None
SCALA_SCALAFIX_CONFIG_FILE	scalafix configuration file name Use `LINTER_DEFAULT` to let the linter find it	`.scalafix.conf`
SCALA_SCALAFIX_RULES_PATH	Path where to find linter configuration file	Workspace folder, then MegaLinter default rules
SCALA_SCALAFIX_DISABLE_ERRORS	Run linter but consider errors as warnings	`false`
SCALA_SCALAFIX_DISABLE_ERRORS_IF_LESS_THAN	Maximum number of errors allowed	`0`
SCALA_SCALAFIX_CLI_EXECUTABLE	Override CLI executable	`['scalafix']`

MegaLinter Flavors

This linter is available in the following flavors

	Flavor	Description	Embedded linters	Info
	all	Default MegaLinter Flavor	127

Behind the scenes

How are identified applicable files

File extensions: .scala

How the linting is performed

scalafix is called one time by identified file (file CLI lint mode)

Example calls

scalafix --check myfile.scala

scalafix --check --config .scalafix.conf myfile.scala

scalafix --config .scalafix.conf myfile.scala

Help content

Scalafix 0.14.4
Usage: scalafix [options] [<path> ...]

Scalafix is a refactoring and linting tool. Scalafix supports both syntactic and
semantic linter and rewrite rules. Syntactic rules can run on source code
without compilation. Semantic rules can run on source code that has been
compiled with the SemanticDB compiler plugin.

Common options:

  --rules | -r [String ...] (default: [])
    Scalafix rules to run, for example ExplicitResultTypes. The syntax for rules is
    documented in
    https://scalacenter.github.io/scalafix/docs/users/configuration#rules

  --files | -f [<path> ...] (default: [])
    Files or directories (recursively visited) to fix.

  --config <path> (default: null)
    File path to a .scalafix.conf configuration file. Defaults to .scalafix.conf in
    the current working directory, if any.

  --check
    Check that all files have been fixed with scalafix, exiting with non-zero code
    on violations. Won't write to files.

  --stdout
    Print fixed output to stdout instead of writing in-place.

  --diff
    If set, only apply scalafix to added and edited files in git diff against the
    master branch.

  --diff-base String (default: null)
    If set, only apply scalafix to added and edited files in git diff against a
    provided branch, commit or tag.

  --scala-version ScalaVersion (default: "2.13.17")
    The major or binary Scala version that the provided files are targeting, or the
    full version that was used to compile them when a classpath is provided.

  --syntactic
    Run only syntactic rules, ignore semantic rules even if they are explicitly
    configured in .scalafix.conf or via --rules

  --triggered
    Overlay the default rules & rule settings in .scalafix.conf with the `triggered`
    section

  --verbose
    Print out additional diagnostics while running scalafix.

  --help | -h
    Print out this help message and exit

  --version | -v
    Print out version number and exit

Semantic options:

  --classpath Classpath (default: "<classpath>")
    Full classpath of the files to fix, required for semantic rules. The source
    files that should be fixed must be compiled with semanticdb-scalac.
    Dependencies are required by rules like ExplicitResultTypes, but the
    dependencies do not need to be compiled with semanticdb-scalac.

  --sourceroot <path> (default: null)
    Absolute path passed to semanticdb with -P:semanticdb:sourceroot:<path>.
    Relative filenames persisted in the Semantic DB are absolutized by the
    sourceroot. Defaults to current working directory if not provided.

  --semanticdb-targetroots [<path> ...] (default: [])
    Absolute paths passed to semanticdb with -P:semanticdb:targetroot:<path>. Used
    to locate semanticdb files. By default, Scalafix will try to locate
    semanticdb files in the classpath

  --auto-classpath
    If set, automatically infer the --classpath flag by scanning for directories
    with META-INF/semanticdb

  --auto-classpath-roots [<path> ...] (default: [])
    Additional directories to scan for --auto-classpath

  --scalac-options [String ...] (default: [])
    The scala compiler options used to compile this --classpath, for example
    -Ywarn-unused-import

Tab completions:

  --bash
    Print out bash tab completions. To install:
    ```
    # macOS, requires "brew install bash-completion"
    scalafix --bash > /usr/local/etc/bash_completion.d/scalafix
    # Linux
    scalafix --bash > /etc/bash_completion.d/scalafix
    ```

  --zsh
    Print out zsh tab completions. To install:
    ```
    scalafix --zsh > /usr/local/share/zsh/site-functions/_scalafix
    unfunction _scalafix
    autoload -U _scalafix
    ```

Less common options:

  --exclude [<glob> ...] (default: [])
    Unix-style glob for files to exclude from fixing. The glob syntax is defined by
    `nio.FileSystem.getPathMatcher`.

  --tool-classpath URLClassLoader (default: "<classloader>")
    Additional classpath for compiling and classloading custom rules, as a set of
    filesystem paths, separated by ':' on Unix or ';' on Windows.

  --charset Charset (default: "UTF-8")
    The encoding to use for reading/writing files

  --no-sys-exit
    If set, throw exception in the end instead of System.exit

  --no-stale-semanticdb
    Don't error on stale semanticdb files.

  --settings ScalafixConfig (default: {})
    Custom settings to override .scalafix.conf

  --out-from String (default: null)
    Write fixed output to custom location instead of in-place. Regex is passed as
    first argument to file.replaceAll(--out-from, --out-to), requires --out-to.

  --out-to String (default: null)
    Companion of --out-from, string that is passed as second argument to
    fileToFix.replaceAll(--out-from, --out-to)

  --auto-suppress-linter-errors
    Insert /* scalafix:ok */ suppressions instead of reporting linter errors.

  --cwd <path> (default: "/")
    The current working directory

Installation on mega-linter Docker image

Dockerfile commands :

# Parent descriptor install
ENV JAVA_HOME=/usr/lib/jvm/java-21-openjdk
ENV PATH="$JAVA_HOME/bin:${PATH}"
RUN curl --retry-all-errors --retry 10 -fLo coursier https://git.io/coursier-cli && \
        chmod +x coursier

# Linter install
RUN ./coursier install scalafix --quiet --install-dir /usr/bin && rm -rf /root/.cache

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