Check Code Duplication
Checks for duplicate functions, methods, constructors and test cases.
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(Pro+) (default), json(Teams+), codeclimate(Teams+), gitlab(Teams+), checkstyle(Teams+), sonar(Teams+)]
-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)
-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}> 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​
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.
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.
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 formatcodeDuplications- 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 fileissues- an array of issues detected in the target file
{
"path": "lib/src/some/file.dart",
"issues": [
...
],
}
The issue object fields are​
declarationType- duplication declaration typedeclarationName- duplication declaration nameduplications- an array of duplication entries for this declarationoffset- a zero-based offset of the class member location in the sourceline- a zero-based line of the class member location in the sourcecolumn- 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 typedeclarationName- duplication entry declaration namerelativePath- path, relative to the root directoryrelativeToFirstDeclarationPath- path, relative to the main code duplication declarationoffset- a zero-based offset of the class member location in the sourceline- a zero-based line of the class member location in the sourcecolumn- 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>
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
}
}
]
}
]
}