doc: wrong layout in static constants that span more than one line in its definition

[japaric]

Example: UserDir in std::io

The UserDir variable, which spans two lines in its definition, gets a boxed layout,

/// A set of permissions for user owned directories, this is equivalent to 0755
/// on unix-like systems.
pub static UserDir: FilePermission = UserRWX | GroupRead | GroupExecute |
                                     OtherRead | OtherExecute;

whereas the one line UserFile definition looks correct

/// A set of permissions for user owned files, this is equivalent to 0644 on
/// unix-like systems.
pub static UserFile: FilePermission = UserRead | UserWrite | GroupRead | OtherRead;

[ipetkov]

Seems like the culprit is wrapping the static value in a pre tag if it has a line break.

Removing wouldn't be a complete solution since for multi-line values it makes sense for a pre html tag to be used over code such as here or here.

Although in certain situations displaying the literal code in a pre tag isn't correct either because the whitespace can get messed up when the code declaration is indented. I think rustdoc should take into account the length of the declaration before the equals sign and trim it from subsequent lines if it is there.

Maybe a simple fix for the above mentioned issue would be for rustdoc to strip out any newlines immediately following an operator (other than a comma)? That way we would remove ambiguity from a short declaration that wraps on a new line from an actual large declaration.