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Check Code Duplication

Checks for duplicate function, methods and constructors.

This command is resistant to some insignificant code changes (for example, a method with renamed parameters or variables is still considered a duplicate) as it performs a structural check rather than an exact match check.

To execute the command, run:

$ dcm check-code-duplication lib # or dcm cd lib

Full command description:

Usage: dcm check-code-duplication [arguments] <directories>
-h, --help                                         Print this usage information.


    --per-package                                  Compare code for duplications only within one package.
    --exclude-overrides                            Exclude methods marked with @override.
    --statements-threshold                         Minimum number of statements inside a declaration block.
                                                   (defaults to "3")


-r, --reporter=<console>                           Analysis output format.
                                                   [console (default), json, codeclimate, gitlab, checkstyle]
-a, --absolute-path                                Show absolute paths in console reporter output.
    --json-path=<path/to/file.json>                Path to the JSON file with the analysis output.


-c, --print-config                                 Print resolved config.


    --root-folder=<./>                             Root folder.
                                                   (defaults to the current directory)
    --sdk-path=<directory-path>                    Dart SDK directory path.
                                                   If the project has a `.fvm/flutter_sdk` symlink, it will be used if the SDK is not found.
    --exclude=<{**/*.g.dart,**/*.freezed.dart}>    File paths in Glob syntax to exclude.
                                                   (defaults to "{**/*.g.dart,**/*.freezed.dart}")


    --no-congratulate                              Don't show output even when there are no issues.


    --verbose                                      Show verbose logs.


    --ci-key                                       The license key to run on CI server. Can be provided via DCM_CI_KEY env variable.
    --email                                        The email used to purchase the license. Can be provided via DCM_EMAIL env variable.


    --no-analytics                                 Disable sending anonymous usage statistics.


    --[no-]fatal-found                             Treat found code duplications as fatal.
                                                   (defaults to on)

Suppressing the command

In order to suppress the command add the ignore: code-duplication comment. To suppress for an entire file add ignore_for_file: code-duplication to the beginning of a file.

Calculating duplication on per-package level

To compare code for duplication only within one package, pass the --per-package CLI flag.

Use this mode if you want to avoid unifying code between several packages.

Excluding overrides

To exclude methods marked with the "@override" annotation, pass the --exclude-overrides CLI flag.

Configuring the minimum number of statements

By default, the command checks for declarations with at least 3 statements and declarations with an expression body (e.g. (String param) => someMethod();).

To configure the minimum number of statements, pass the --statements-threshold CLI option.

info

Blocks with a single return statement and expression bodies are handled differently. This configuration does not affect them.

Output example

Console

Use --reporter=console to enable this format.

JSON

The reporter prints a single JSON object containing meta information and the list of duplication issues.

Use --reporter=json to enable this format.

The root object fields are

• formatVersion - an integer representing the format version (will be incremented each time the serialization format changes)
• timestamp - a creation time of the report in YYYY-MM-DD HH:MM:SS format
• codeDuplications - an array of code duplication issues

{
  "formatVersion": 2,
  "timestamp": "2021-04-11 14:44:42",
  "codeDuplications": [
    {
      ...
    },
    {
      ...
    },
    {
      ...
    }
  ]
}

The codeDuplication object fields are

• path - a relative path of the unused file
• issues - an array of issues detected in the target file

{
  "path": "lib/src/some/file.dart",
  "issues": [
    ...
  ],
}

The issue object fields are

• declarationType - duplication declaration type
• declarationName - duplication declaration name
• duplications - an array of duplication entries for this declaration
• offset - a zero-based offset of the class member location in the source
• line - a zero-based line of the class member location in the source
• column - a zero-based column of class member the location in the source

{
  "declarationType": "function",
  "declarationName": "myFunction",
  "duplications": [
    ...
  ],
  "offset": 156,
  "line": 7,
  "column": 1
}

The duplication object fields are

• declarationType - duplication entry declaration type
• declarationName - duplication entry declaration name
• relativePath - path, relative to the root directory
• relativeToFirstDeclarationPath - path, relative to the main code duplication declaration
• offset - a zero-based offset of the class member location in the source
• line - a zero-based line of the class member location in the source
• column - a zero-based column of class member the location in the source

{
  "declarationType": "method",
  "declarationName": "someMethod",
  "relativePath": "lib/src/some/another_file.dart",
  "relativeToFirstDeclarationPath": "./another_file.dart",
  "offset": 156,
  "line": 7,
  "column": 1
}

GitLab

Reports unused code issues in merge requests based on Code Quality custom tool. Use --reporter=gitlab to enable this format.

Checkstyle

Use --reporter=checkstyle to enable this format.

<?xml version="1.0"?>
<checkstyle version="10.0">
  <file name="example.dart">
    <error line="5" column="3" severity="warning" message="This function has 2 duplicate declarations" source="duplication-issue"/>
  </file>
  <file name="relative_root.dart">
    <error line="5" column="3" severity="warning" message="This method is a duplicate of doWork (located at example.dart). Target declaration has 1 other duplicate." source="duplication-issue"/>
    <error line="5" column="3" severity="warning" message="This function is a duplicate of doWork (located at example.dart). Target declaration has 1 other duplicate." source="duplication-issue"/>
  </file>
</checkstyle>