fix(variables): pre-commit check to enforce variables in variables file

This adds a check to enforce that variables are all defined in files that have the following format
`variables[.grouping].tf`.

.pre-commit-hooks.yaml

@@ -0,0 +1,11 @@
+######################
+# Yaml related hooks
+# These only have shell dependencies
+- id: vars-in-variables-files
+  name: "Ensure that all variables are defined in files that have the following name format: `variables[.grouping].tf`"
+  description: "Errors if a variable is defined in a file that does not start with `variables.`"
+  entry: hooks/vars-in-variables-files/check
+  language: script
+  files: \.tf$
+  exclude: ^variables\..*\.tf$
+  ######################

hooks/vars-in-variables-files/check

@@ -0,0 +1,23 @@
+#!/bin/bash -e
+
+check_files() {
+	has_error=0
+	for file in "$@"; do
+
+		# grep the file to see if it has a line that start with 'variable "'
+		if [[ "$file" == */variables.*tf ]]; then
+			echo "variables file ok: $file"
+		elif grep -q "^variable \"" "$file"; then
+			echo "ERROR: $file MUST not contain variables"
+			has_error=1
+		fi
+	done
+	return $has_error
+}
+
+if ! check_files "$@"; then
+	echo "Variables defined in files that do not match our naming convention: 'variables[.grouping].tf'"
+	echo "See: https://open-turo.github.io/standards-terraform/modules/input-variables/"
+fi
+
+exit $has_error

hooks/vars-in-variables-files/fixtures/bad.tf

@@ -0,0 +1,4 @@
+variable "should_fail" {
+  default = "true"
+  description = "This should fail because it isn't in file that starts with variables.tf"
+}

hooks/vars-in-variables-files/fixtures/variables.function.tf

@@ -0,0 +1,4 @@
+variable "test" {
+  default = "test"
+  description = "Simple variable"
+}

hooks/vars-in-variables-files/test

@@ -0,0 +1,19 @@
+#!/bin/bash -e
+
+# get the directory of the script
+script_directory="$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)"
+
+echo "testing: $script_directory"
+
+echo "testing: check $script_directory/fixtures/variables.function.tf"
+"$script_directory/check" "$script_directory/fixtures/variables.function.tf"
+
+# check to see if the next file failed
+echo "testing: check $script_directory/fixtures/bad.tf"
+echo "         expecting error"
+if "$script_directory/check" "$script_directory/fixtures/bad.tf"; then
+	echo "ERROR: should have failed"
+	exit 1
+fi
+
+echo "testing: PASS"

script/test

@@ -0,0 +1,5 @@
+#!/bin/bash -e
+
+REPO_DIR="$(dirname "$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null 2>&1 && pwd)")"
+
+"$REPO_DIR/hooks/variables/test"