A moderately (dis)organized list of features related to dealing with whitespace issues in Git, in no particular order.

Flag whitespace errors:

$ git diff --check

Other possibilities:

--ignore-space-at-eol
    Ignore changes in whitespace at EOL.

-b, --ignore-space-change
    Ignore changes in amount of whitespace. This ignores whitespace at line end, and
    considers all other sequences of one or more whitespace characters to be equivalent.

-w, --ignore-all-space
    Ignore whitespace when comparing lines. This ignores differences even if one line has
    whitespace where the other line has none.

--ignore-blank-lines
    Ignore changes whose lines are all blank.

Recursive merge options:

ignore-space-change, ignore-all-space, ignore-space-at-eol, ignore-cr-at-eol
    Treats lines with the indicated type of whitespace change as unchanged for the sake
    of a three-way merge. Whitespace changes mixed with other changes to a line are not
    ignored. See also git-diff(1) -b, -w, --ignore-space-at-eol, and --ignore-cr-at-eol.

    ·   If their version only introduces whitespace changes to a line, our version is
        used;

    ·   If our version introduces whitespace changes but their version includes a
        substantial change, their version is used;

    ·   Otherwise, the merge proceeds in the usual way.

--ignore-whitespace, --whitespace=<option>
    These flag are passed to the git apply program (see git-apply(1)) that applies
    the patch. Incompatible with the --interactive option.

From man git-apply:

--ignore-space-change, --ignore-whitespace
    When applying a patch, ignore changes in whitespace in context lines if
    necessary. Context lines will preserve their whitespace, and they will not
    undergo whitespace fixing regardless of the value of the --whitespace option.
    New lines will still be fixed, though.

--whitespace=<action>
    When applying a patch, detect a new or modified line that has whitespace
    errors. What are considered whitespace errors is controlled by core.whitespace
    configuration. By default, trailing whitespaces (including lines that solely
    consist of whitespaces) and a space character that is immediately followed by
    a tab character inside the initial indent of the line are considered
    whitespace errors.

    By default, the command outputs warning messages but applies the patch. When
    git-apply is used for statistics and not applying a patch, it defaults to
    nowarn.
    
    You can use different <action> values to control this behavior:

    ·   nowarn turns off the trailing whitespace warning.

    ·   warn outputs warnings for a few such errors, but applies the patch as-is
        (default).

    ·   fix outputs warnings for a few such errors, and applies the patch after
        fixing them (strip is a synonym --- the tool used to consider only
        trailing whitespace characters as errors, and the fix involved stripping
        them, but modern Gits do more).

    ·   error outputs warnings for a few such errors, and refuses to apply the
        patch.

    ·   error-all is similar to error but shows all errors.