Add requirements and strong preferences

index.html

@@ -897,6 +897,103 @@ <h2>How are errors modeled?</h2>
 						</code></pre>
 					</section>
 				</section>
+				<section>
+					<section>
+						<h2>What are requirements and strong preferences?</h2>
+					</section>
+					<section>
+						Enforce constraints from <code>package.py</code> or configuration
+					</section>
+					<section>
+						In a recipe:
+						<pre><code data-trim data-noescape class="python">
+						class Hdf5(CMakePackage):
+
+							requires("%gcc", msg="This package must be built with GCC")
+						</code></pre>
+						From configuration:
+						<pre><code data-trim data-noescape class="YAML">
+						packages:
+							hdf5:
+								require:
+								- spec: "%gcc"
+								  message: "This package must be built with GCC"
+						</code></pre>
+					</section>
+					<section>
+						Setting default requirements
+						<pre><code data-trim data-noescape class="YAML">
+						packages:
+							all:
+								require: 
+								- "+shared +cuda"
+						</code></pre>
+						vs.
+						<pre><code data-trim data-noescape class="YAML">
+						packages:
+							all:
+								require: 
+								- "+shared"
+								- "+cuda"
+						</code></pre>
+					</section>
+					<section>
+						Package specific requirements override defaults
+						<pre><code data-trim data-noescape class="YAML">
+							packages:
+								all:
+									require:
+									- 'build_type=Debug'
+									- '%clang'
+								cmake:
+									require:
+									- '%gcc'
+						</code></pre>
+					</section>
+					<section>
+						Requirements on virtual packages
+						<pre><code data-trim data-noescape class="YAML">
+							packages:
+								mpi:
+									require: 
+									- 'mvapich2 %gcc'
+								mvapich2:
+									require: 
+									- '~cuda'
+						</code></pre>
+					</section>
+					<section>
+					Strong preferences
+					<pre><code data-trim data-noescape class="YAML">
+						packages:
+							all:
+								prefer:
+								- 'build_type=Release'
+								- '+cuda'
+					</code></pre>
+					==
+					<pre><code data-trim data-noescape class="YAML">
+						packages:
+							all:
+								require:
+								- any_of: ['build_type=Release', '@:']
+								- any_of: ['+cuda', '@:']
+					</code></pre>
+					</section>
+					<section>
+						<h2>Hands-on</h2>
+						<pre><code data-trim data-noescape class="bash">
+							# Add a requirement to configuration,
+							# try to violate it, check the error message
+
+							# Do the same with a strong preference, observe 
+							# spack solve weights
+
+							# Enforce virtuals in an environment using 
+							# requirements
+						</code></pre>
+					</section>
+				</section>
 			</div>
 		</div>