From 2871b670f47b7d04d18abae56ce23ffd38a32249 Mon Sep 17 00:00:00 2001
From: Mitja Felicijan <mitja.felicijan@gmail.com>
Date: Sun, 12 May 2024 03:25:48 +0200
Subject: Added .assure extension

---
 Makefile  |  4 +++-
 README.md | 29 +++++++++++++++++++++++++++--
 makext.mk | 20 ++++++++++++++++++++
 3 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 37470e7..2869487 100644
--- a/Makefile
+++ b/Makefile
@@ -1,11 +1,13 @@
 MK_DESCRIPTION="This provides some additional tools for makefiles."
 MK_LICENSE="Released under the BSD two-clause license, see the LICENSE file for more information."
+MK_ASSURE="python3 ls tree clang"
 
 include makext.mk
 
 help: .help
 
-demo: .assure
+demo-assure: .assure
+	@echo "All good, continuing..."
 
 build-app: clean-cache # Build the application
 	@echo "Building the application..."
diff --git a/README.md b/README.md
index c6aca6b..5f8fd86 100644
--- a/README.md
+++ b/README.md
@@ -11,9 +11,13 @@ tasks.
 > meant to really be a task runner. Keep that in mind. However, dispite
 > that, I constantly find myself using it as such.
 
-Features include:
+| Extension | Description                                         |
+|-----------|-----------------------------------------------------|
+| .help     | Displays all targets with a comment in help format. |
+| .assure   | Check for the existance of programs on a machine.   |
+
+Additional features:
 
-- Enhanced help message generation with support for custom descriptions.
 - Automatic description inclusion in help message.
 - Automatic license inclusion in help message.
 
@@ -131,6 +135,27 @@ Released under the BSD two-clause license, see the LICENSE file for
 more information.
 ```
 
+## Assure extension
+
+Often times project uses multiple programs and to ensure that these
+programs are already installed before recipes are executed `assure` can
+be used. If programs are missing recipes can only partially be executed
+leaving project in a potentially broken state.
+
+```make
+MK_ASSURE="python3 ls tree clang"
+
+include makext.mk
+
+build-app: .assure
+	@echo "Building the application..."
+```
+
+`.assure` prerequisite will loop over the list of programs defined in
+`MK_ASSURE` variable and in case one is missing will exit `make` with
+status code error 1. This will stop executing the recipe and therefore
+not execute anything in target `build-app`.
+
 ## Acknowledgement
 
 - https://stackoverflow.com/a/59087509
diff --git a/makext.mk b/makext.mk
index 06953c5..b4846c0 100644
--- a/makext.mk
+++ b/makext.mk
@@ -15,6 +15,11 @@
 # `makext` was written by Mitja Felicijan and is released under the BSD
 # two-clause license, see the LICENSE file for more information.
 
+# Checks if operating system is Windows and exists with error.
+ifeq ($(OS),Windows_NT)
+$(error makext does not support Windows operating system)
+endif
+
 # Help extension that lists all the targets with descriptions
 # and adds description and license information if data provided.
 .PHONY: .help
@@ -27,3 +32,18 @@ endif
 ifdef MK_LICENSE
 	@echo "\n$(MK_LICENSE)" | fmt
 endif
+
+# Checks `MK_ASSURE` variable if all the programs declared actually
+# exist on a machine. If not this exists make with error.
+.PHONY: .assure
+.assure:
+ifndef MK_ASSURE
+	@echo "Variable MK_ASSURE is not defined. Can not check for programs."
+else
+	@for prog in $(shell echo $(MK_ASSURE)); do \
+		if ! which $$prog > /dev/null; then \
+			echo "Error: '$$prog' not found on this machine."; \
+			exit 1; \
+		fi; \
+	done
+endif
-- 
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