I've decided to close this PR. The goal was to make .ejs files more readable and to adhere to conventions regarding the SPEC file. This is not possible if using lodash. We can make our code very readable, but that would make the SPEC file way out of line from conventions. If trying to comply with conventions, the ejs files will become less readable; and it's virtually impossible to 100% comply with conventions using lodash (regardless of readability), a different library is needed for this.
The current code it's not perfect, but it's working. Unless we change -common to use ejs for templates, this PR is unnecessary.

I'm reopening this PR. With some help from others, I'm using the function print, which is built into lodash, to better control inserting an empty line.
The new code is much more readable, and it always adheres to the guidelines.

@malept it's ready for review

Here's an example of how the output will look like with :

{
  name: 'name',
  compressionLevel: 2,
  version: 3,
  revision: 1,
  productName: 'productName',
  genericName: 'genericName',
  description: 'description',
  productDescription: 'prodDesc',
  license: 'license',
  homepage: 'http://homepage.com',
  requires: ['r1', 'r2'],
  execArguments: undefined,
  categories: ['c1', 'c2', 'c3'],
  mimeType: ['m1', 'm2'],
  icon: 'test/fixtures/scaled-icon.png',
  pre: 'pre',
  preun: 'preun',
  post: 'post',
  postun: 'postun'
}

%define _binary_payload w2.xzdio

Name: name
Version: 3
Release: 1%{?dist}
Summary: description

License: license
URL: http://homepage.com

Requires: r1, r2
AutoReqProv: no

%description
prodDesc


%install
mkdir -p %{buildroot}/usr/
cp -r usr/* %{buildroot}/usr/


%files
/usr/bin/name
/usr/lib/name/
/usr/share/applications/name.desktop
/usr/share/doc/name/
/usr/share/pixmaps/name.png


%pre
pre


%preun
preun


%post
post


%postun
postun

The spacing between sections will stay the same, even if any of the optional sections are undefined.

Another example:

{
  name: 'name',
  compressionLevel: 2,
  version: 3,
  revision: 1,
  productName: 'productName',
  genericName: 'genericName',
  description: undefined,
  productDescription: undefined,
  license: undefined,
  homepage: 'http://homepage.com',
  requires: ['r1', 'r2'],
  execArguments: undefined,
  categories: ['c1', 'c2', 'c3'],
  mimeType: ['m1', 'm2'],
  icon: 'test/fixtures/scaled-icon.png',
  pre: undefined,
  preun: 'preun',
  post: undefined,
  postun: undefined
}

%define _binary_payload w2.xzdio

Name: name
Version: 3
Release: 1%{?dist}

URL: http://homepage.com

Requires: r1, r2
AutoReqProv: no

%install
mkdir -p %{buildroot}/usr/
cp -r usr/* %{buildroot}/usr/


%files
/usr/bin/name
/usr/lib/name/
/usr/share/applications/name.desktop
/usr/share/doc/name/
/usr/share/pixmaps/name.png


%preun
preun

Any difference in how the .desktop files are rendered?

Any difference in how the .desktop files are rendered?

There's no difference for that one. The changes there better show which arguments are optional, and which ones are mandatory