added a comment - - edited
Stefano Kowalke The length parameter for MySQL's integer does not have any effect unless you use it in conjunction with the ZEROFILL attribute. It does not have any meaning concerning min or max value and the storage requirements for that specific type but only specifies the display length for zerofill characters.
M indicates the maximum display width for integer types. For floating-point and fixed-point types, M is the total number of digits that can be stored. For string types, M is the maximum length. The maximum allowable value of M depends on the data type.
As MySQL does not have a native boolean type, Doctrine uses it to map it's own boolean type as it is the one that comes closest to a "boolean" type column. This is not a bug in Doctrine but an expected behaviour.
Hope I could clarify this.