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Check Code Duplication

Reports duplicate functions, methods, constructors and test cases.

info

The duplicate detection algorithm 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" (--output-format)         Analysis output format.
                                                   [console (default), json, codeclimate, gitlab, checkstyle, sonar]
-a, --absolute-path                                Show absolute paths in console reporter output.
    --output-to="path/to/file"                     Path to the file with the analysis output.


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


    --root-folder="./"                             Root folder.
                                                   (defaults to the current directory)
-s, --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.
-e, --exclude="{**/*.g.dart,**/*.freezed.dart}"    Files to exclude (in Glob syntax).
                                                   (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 duplicate code as fatal.
                                                   (defaults to on)

Suppressing the Command​

To suppress issues produced by the command, use the ignore: code-duplication comment. To suppress the command for an entire file, add the ignore_for_file: code-duplication comment 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.

Detecting Duplicate Test Cases​

To detect duplicate test cases, run the command against your tests directory (for example, dcm check-code-duplication test).

The command will then analyze all test invocations (for example, test(...), testWidget(...), and every other invocations that is marked with @isTest under the hood) and include duplicate cases into the output.

Output Example​

Console (default)​

Use --reporter=console to get output in console format.

Console

JSON​

Use --reporter=json to get output as a single JSON object containing metadata and the list of duplication issues.

Format specification

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
  • duplicationResults - an array of objects
  • summary - an array of objects
{
  "formatVersion": 10,
  "timestamp": "2021-04-11 14:44:42",
  "duplicationResults": [
    {
      ...
    },
    {
      ...
    },
    {
      ...
    }
  ],
  "summary": [
    {
      ...
    },
    {
      ...
    }
  ]
}

The result object fields are​

  • path - the relative path to the file with issues
  • issues - an array of issues detected in the target file
{
  "path": "lib/src/some/file.dart",
  "issues": [
    ...
  ],
}

The issue object fields are​

  • id - issue id
  • message - the message associated with the issue
  • location - the location associated with the issue
  • effortInMinutes - an estimated effort to fix the issue (in minutes)
  • declarationType - duplication declaration type
  • declarationName - duplication declaration name
  • duplications - an array of duplication entries for this declaration
{
  "id": "duplication-issue",
  "message": "This method has 1 duplicate declaration",
  "location": {
    ...
  },
  "effortInMinutes": 20,
  "declarationName": "build",
  "declarationType": "method",
  "duplications": [
    ...
  ]
}

The duplication object fields are​

  • declarationType - duplication entry declaration type
  • declarationName - duplication entry declaration name
  • location - the location associated with the entry
  • relativePath - path, relative to the root directory
  • relativeToFirstDeclarationPath - path, relative to the main code duplication declaration
{
  "declarationType": "method",
  "declarationName": "someMethod",
  "location": {
    ...
  },
  "relativePath": "lib/src/some/another_file.dart",
  "relativeToFirstDeclarationPath": "./another_file.dart",
}

The location object fields are​

  • startColumn - the start column of the entity
  • startLine - the start line of the entity
  • endColumn - the end column of the entity
  • endLine - the end line of the entity
  • startOffset - the offset of the entity
{
  "endColumn": 2,
  "endLine": 90,
  "startColumn": 1,
  "startLine": 48,
  "startOffset": 1638
}

The summary-record object fields are​

  • title - a message with the summary entry title
  • value - the actual value of the entry
{
  "title": "Total code duplication",
  "value": 1
}
Old format specification (prior to DCM 1.26.0)

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​

Use --reporter=gitlab to get output in a GitLab-compatible format. To learn how to integrate DCM with GitLab, refer to this guide.

Code Climate​

Use --reporter=codeclimate to get output in Code Climate format.

Output example
{"type":"issue","check_name":"duplication-issue","description":"This method has 1 duplicate declaration","categories":["Duplication"],"location":{"path":"lib/src/sheets/macos_sheet.dart","positions":{"begin":{"column":3,"line":168},"end":{"column":4,"line":179}}},"severity":"major","fingerprint":"58e573c82a01a5be2ee4d8b8360b8978"}
{"type":"issue","check_name":"duplication-issue","description":"This method is a duplicate of buildPage (located at lib/src/sheets/macos_sheet.dart).","categories":["Duplication"],"location":{"path":"lib/src/dialogs/macos_alert_dialog.dart","positions":{"begin":{"column":3,"line":310},"end":{"column":4,"line":321}}},"severity":"major","fingerprint":"f2278858ccdb8268971fa038fa4b9ca8"}

Checkstyle​

Use --reporter=checkstyle to get output in Checkstyle format.

Output example
<?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>
note

Checkstyle format is supported by Bitbucket. To learn how to integrate DCM with Bitbucket, refer to this guide.

Sonar​

Use --reporter=sonar to get output in SonarQube's generic format for external issues.

Output example
{
  "rules": [
    {
      "cleanCodeAttribute": "CLEAR",
      "description": "To learn more, visit the documentation https://dcm.dev/docs/cli/code-quality-checks/code-duplication/",
      "engineId": "dcm",
      "id": "duplication-issue",
      "impacts": [
        {
          "severity": "MEDIUM",
          "softwareQuality": "MAINTAINABILITY"
        }
      ],
      "name": "duplication-issue"
    }
  ],
  "issues": [
    {
      "effortMinutes": 20,
      "primaryLocation": {
        "filePath": "lib/src/unused_code_widget.dart",
        "message": "This method has 1 duplicate declaration",
        "textRange": {
          "endColumn": 4,
          "endLine": 34,
          "startColumn": 3,
          "startLine": 31
        }
      },
      "ruleId": "duplication-issue",
      "secondaryLocations": [
        {
          "filePath": "lib/src/unused_widget.dart",
          "message": "This method is a duplicate of build (located at lib/src/unused_code_widget.dart).",
          "textRange": {
            "endColumn": 4,
            "endLine": 17,
            "startColumn": 3,
            "startLine": 14
          }
        }
      ]
    }
  ]
}
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