Activate MSVC during CMake setup for NMake

CI/before_script.msvc.sh

@@ -33,7 +33,20 @@ function unixPathAsWindows {
 		cygpath -w $1
 	else
 		echo "$1" | sed "s,^/\([^/]\)/,\\1:/," | sed "s,/,\\\\,g"
+	fi
+}
 
+function windowsSystemPathAsUnix {
+	if command -v cygpath >/dev/null 2>&1; then
+		cygpath -u -p $1
+	else
+		IFS=';' read -r -a paths <<< "$1"
+		declare -a convertedPaths
+		for entry in paths; do
+			convertedPaths+=(windowsPathAsUnix $entry)
+		done
+		convertedPath=printf ":%s" ${convertedPaths[@]}
+		echo ${convertedPath:1}
 	fi
 }
 
@@ -54,6 +67,8 @@ CONFIGURATION=""
 TEST_FRAMEWORK=""
 GOOGLE_INSTALL_ROOT=""
 
+ACTIVATE_MSVC=""
+
 while [ $# -gt 0 ]; do
 	ARGSTR=$1
 	shift
@@ -139,7 +154,7 @@ EOF
 done
 
 if [ -n "$NMAKE" ]; then
-	command -v nmake -? >/dev/null 2>&1 || { echo "Error: nmake (NMake) is not on the path. Make sure you have the necessary environment variables set for command-line C++ development (for example, by starting from a Developer Command Prompt)."; exit 1; }
+	ACTIVATE_MSVC=true
 fi
 
 if [ -z $VERBOSE ]; then
@@ -385,6 +400,44 @@ echo "Starting prebuild on MSVC${MSVC_DISPLAY_YEAR} WIN${BITS}"
 echo "==================================="
 echo
 
+if ! [ -z $ACTIVATE_MSVC ]; then
+	echo "Activating MSVC in the current shell."
+	command -v vswhere >/dev/null 2>&1 || { echo "Error: vswhere is not on the path."; exit 1; }
+
+	# capture CMD environment so we know what's been changed
+	declare -A originalCmdEnv
+	originalIFS="$IFS"
+	IFS=$'\n\r'
+	for pair in $(cmd //c "set"); do
+		IFS='=' read -r -a separatedPair <<< "${pair}"
+		originalCmdEnv["${separatedPair[0]}"]="${separatedPair[1]}"
+	done
+
+	MSVC_INSTALLATION_PATH=$(vswhere -legacy -version $MSVC_VER -property installationPath)
+	# capture CMD environment in a shell with MSVC activated
+	if [ $MSVC_REAL_VER -ge 15 ]; then
+		cmdEnv="$(cmd //c "${MSVC_INSTALLATION_PATH}\Common7\Tools\VsDevCmd.bat" -no_logo -arch=$([ $BITS -eq 64 ] && echo "amd64" || echo "x86") -host_arch=$([ $(uname -m) == 'x86_64' ] && echo "amd64" || echo "x86") "&&" set)"
+	else
+		echo "MSVC 2015 and older not yet supported"
+		exit 1
+	fi
+
+	declare -A cmdEnvChanges
+	for pair in $cmdEnv; do
+		IFS='=' read -r -a separatedPair <<< "${pair}"
+		key="${separatedPair[0]}"
+		value="${separatedPair[1]}"
+		if ! [ ${originalCmdEnv[$key]+_} ] || [ "${originalCmdEnv[$key]}" != "$value" ]; then
+			if [ $key != 'PATH' ] && [ $key != 'path' ] && [ $key != 'Path' ]; then
+				export "$key=$value"
+			else
+				export PATH=$(windowsSystemPathAsUnix $value)
+			fi
+		fi
+	done
+	IFS="$originalIFS"
+fi
+
 # cd OpenMW/AppVeyor-test
 mkdir -p deps
 cd deps