Add dependency check for the builds. (#568)

* Add dependency check for the builds.

* Use Python 3 specifically.

* Use the right target.

.gitignore

@@ -10,6 +10,7 @@ __pycache__
 geckodriver.log
 firefox/
 .vscode
+.idea
 
 build
 downloads

Makefile

@@ -1,5 +1,6 @@
 PYODIDE_ROOT=$(abspath .)
 include Makefile.envs
+.PHONY=check
 
 FILEPACKAGER=$(PYODIDE_ROOT)/tools/file_packager.py
 
@@ -58,7 +59,8 @@ PARSO_LIBS=$(PARSO_ROOT)/__init__.py
 
 SITEPACKAGES=root/lib/python$(PYMINOR)/site-packages
 
-all: build/pyodide.asm.js \
+all: check \
+	build/pyodide.asm.js \
 	build/pyodide.asm.data \
 	build/pyodide.js \
 	build/pyodide_dev.js \
@@ -250,3 +252,6 @@ emsdk/emsdk/.complete:
 	make -C emsdk
 
 FORCE:
+
+check:
+	./tools/dependency-check.sh

tools/dependency-check.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+
+failure_exit() {
+  echo >&2 "Could not find ${1}.  Please install that before continuing."
+  exit 1
+}
+
+check_python_headers() {
+  local python_headers_present
+  python_headers_present="$(pkg-config --libs python-3.7)"
+
+  if [ ! "${python_headers_present}" ]; then
+    failure_exit "Python 3.7 headers"
+  fi
+}
+
+check_binary_present() {
+  local binary_exists
+  binary_exists="$(command -v "${1}")"
+  if [ ! "${binary_exists}" ]; then
+    failure_exit "${1}"
+  fi
+}
+
+check_fortran_dependencies() {
+  check_binary_present "gfortran"
+  check_binary_present "f2c"
+}
+
+check_js_dependencies() {
+  check_binary_present "lessc"
+  check_binary_present "uglifyjs"
+}
+
+check_pyyaml() {
+  local pyyaml_import_check
+  pyyaml_import_check="$(python3 -c 'import yaml')"
+  if [ "${pyyaml_import_check}" ]; then
+    failure_exit "PyYAML"
+  fi
+}
+
+check_python_headers
+check_fortran_dependencies
+check_js_dependencies
+check_pyyaml