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mccabe-cyclomatic

Calculates Thomas McCabe's cyclomatic complexity for a go file or package

Install

go get github.com/freenerd/mccabe-cyclomatic

Usage

To get the cyclomatic complexity of a file:

  $ mccabe-cyclomatic -f ./example/example.go
  7

To get the cyclomatic complexity of a package:

  $ mccabe-cyclomatic -p github.com/freenerd/mccabe-cyclomatic
  5

The output is the cyclomatic complexity number.

Calculation

complexity = number of code execution branch statements + 1

The file to be analyzed is loaded with go/parser ParseFile and subsequentially walked with a go/ast Visitor. Depending on which ast node types are encountered, the complexity count is increased.

Effective Go describes the following code execution branch statements:

• if
• for
• switch
• select

These can be mapped to certain Go ast node types:

• if is of IfStmt type. An else if is of IfStmt type as well. An else clause does not add cyclomatic complexity.
• for is either of ForStmt type or of RangeStmt type.
• switch might either be an expression switch or a type switch. In both cases, the number of code execution branches to be executed is determined by the number of case statements CaseClause. Therefore, we only count each CaseClause. default clauses do not add to cyclomatic complexity.
• select is similar to switch, in that its code execution branches are determined by the number of case statements, but of type CommClause. default clauses do not add to cyclomatic complexity.

We end up with the list of the following ast node types, that determine a new code execution branch:

• IfStmt
• ForStmt
• RangeStmt
• CaseClause
• CommClause

When any of these node types is encounterd, the complexity score is increased by 1.

Apart from the ones just listed, the go language specification includes more [control execution statements]((http://golang.org/ref/spec#Statements). These have not been recognized here: it is assumed that they do not add additional cyclomatic complexity, since they do not add a new code execution branch.

Limitations

• complexity numbers are only returned for whole packages or files, but not for individual functions.
• the package algorithm is not recursive, it will not recognize sub-packages.

References

http://www.literateprogramming.com/mccabe.pdf A Complexity Measure, by Thomas J McCabe. 1976

http://www.win.tue.nl/~aserebre/2IS55/2010-2011/10.pdf

https://en.wikipedia.org/wiki/Cyclomatic_complexity

https://github.com/philbooth/escomplex