14.1.3.3 Complexity Metrics Control

For a program unit that is an executable body (a subprogram body (including generic bodies), task body, entry body or a package body containing its own statement sequence) gnatmetric computes the following complexity metrics:

• McCabe cyclomatic complexity;
• McCabe essential complexity;
• maximal loop nesting level

The McCabe complexity metrics are defined in http://www.mccabe.com/pdf/nist235r.pdf

According to McCabe, both control statements and short-circuit control forms should be taken into account when computing cyclomatic complexity. For each body, we compute three metric values:

• the complexity introduced by control statements only, without taking into account short-circuit forms,
• the complexity introduced by short-circuit control forms only, and
• the total cyclomatic complexity, which is the sum of these two values.

When computing cyclomatic and essential complexity, gnatmetric skips the code in the exception handlers and in all the nested program units.

By default, all the complexity metrics are computed and reported. For more fine-grained control you can use the following switches:

--complexity-all

Report all the complexity metrics

--no-complexity-all

Do not report any of complexity metrics

--complexity-cyclomatic

Report the McCabe Cyclomatic Complexity

--no-complexity-cyclomatic

Do not report the McCabe Cyclomatic Complexity

--complexity-essential

Report the Essential Complexity

--no-complexity-essential

Do not report the Essential Complexity

--loop-nesting

Report maximal loop nesting level

--no-loop-nesting

Do not report maximal loop nesting level

--complexity-average

Report the average McCabe Cyclomatic Complexity for all the subprogram bodies, task bodies, entry bodies and statement sequences in package bodies. The metric is computed and reported for whole set of processed Ada sources only.

--no-complexity-average

Do not report the average McCabe Cyclomatic Complexity for all the subprogram bodies, task bodies, entry bodies and statement sequences in package bodies

-ne

Do not consider exit statements as gotos when computing Essential Complexity

--extra-exit-points

Report the extra exit points for subprogram bodies. As an exit point, this metric counts return statements and raise statements in case when the raised exception is not handled in the same body. In case of a function this metric subtracts 1 from the number of exit points, because a function body must contain at least one return statement.

--no-extra-exit-points

Do not report the extra exit points for subprogram bodies