chore(build): clarify prerequisites in CONTRIBUTING and verify before…

… build (#14642)

The build script at the top level of the repository performs a prerequisites check before beginning the build. This verification is not complete as it does not include the required checks for .NET and Python executables. Further, the prerequisites documentation in the contributing guide does not note the Docker requirement.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

CONTRIBUTING.md

@@ -56,6 +56,8 @@ The following tools need to be installed on your system prior to installing the
 - [Yarn >= 1.19.1, < 2](https://yarnpkg.com/lang/en/docs/install)
 - [.NET Core SDK 3.1.x](https://www.microsoft.com/net/download)
 - [Python >= 3.6.5, < 4.0](https://www.python.org/downloads/release/python-365/)
+- [Docker >= 19.03](https://docs.docker.com/get-docker/)
+  - the Docker daemon must also be running
 
 First fork the repository, and then run the following commands to clone the repository locally.
 
@@ -113,8 +115,9 @@ However, if you wish to build the the entire repository, the following command w
 
 ```console
 cd <root of the CDK repo>
-yarn build
+scripts/foreach.sh yarn build
 ```
+Note: The `foreach` command is resumable by default; you must supply `-r` or `--reset` to start a new session.
 
 You are now ready to start contributing to the CDK. See the [Pull Requests](#pull-requests) section on how to make your
 changes and submit it as a pull request.

scripts/check-build-prerequisites.sh

@@ -42,15 +42,15 @@ app_v=$(node --version)
 # Check for version 10.*.* - 29.*.*
 echo -e "Checking node version... \c"
 if [ $(echo $app_v | grep -c -E "v[12][0-9]\.[0-9]+\.[0-9]+") -eq 1 ]
-then    
+then
     # Check for version 13.0 to 13.6
     if [ $(echo $app_v | grep -c -E "v13\.[0-6]\.[0-9]+") -eq 1 ]
     then
         die "node versions 13.0.0 to 13.6.0 are not supported due to compatibility issues with our dependencies."
     else
         # Check for version < 10.13
         if [ $(echo $app_v | grep -c -E "v10\.([0-9]|1[0-2])\.[0-9]+") -eq 1 ]
-        then   
+        then
             wrong_version
         else
             echo "Ok"
@@ -68,7 +68,7 @@ check_which $app $app_min
 app_v=$(${app} --version)
 echo -e "Checking yarn version... \c"
 if [ $(echo $app_v | grep -c -E "1\.(19|2[0-9])\.[0-9]+") -eq 1 ]
-then   
+then
     echo "Ok"
 else
     wrong_version
@@ -83,9 +83,34 @@ check_which $app $app_min
 echo -e "Checking if docker is running... \c"
 docker_running=$(docker ps)
 if [ $? -eq 0 ]
-then    
+then
     echo "Ok"
 else
     die "Docker is not running"
 fi
 
+# [.NET == 3.1.x]
+app="dotnet"
+app_min="3.1.0"
+check_which $app $app_min
+app_v=$(${app} --version)
+echo -e "Checking dotnet version... \c"
+if [ $(echo $app_v | grep -c -E "3\.1\.[0-9]+") -eq 1 ]
+then
+    echo "Ok"
+else
+    wrong_version
+fi
+
+# [Python >= 3.6.5, < 4.0]
+app="python3"
+app_min="3.6.5"
+check_which $app $app_min
+app_v=$(${app} --version)
+echo -e "Checking python3 version... \c"
+if [ $(echo $app_v | grep -c -E "3\.[6-9]+\.[0-9]+") -eq 1 ]
+then
+    echo "Ok"
+else
+    wrong_version
+fi