Lint and fix missing trailing newlines (#16445)

Apply the Clojure Style Guide recommendation to end files with proper lines
(having a trailing newline character). See
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_206

Makefile

@@ -14,17 +14,17 @@ WHITE  := $(shell tput -Txterm setaf 7)
 YELLOW := $(shell tput -Txterm setaf 3)
 RESET  := $(shell tput -Txterm sgr0)
 HELP_FUN = \
-		   %help; \
-		   while(<>) { push @{$$help{$$2 // 'options'}}, [$$1, $$3] if /^([a-zA-Z\-]+)\s*:.*\#\#(?:@([a-zA-Z\-]+))?\s(.*)$$/ }; \
-		   print "Usage: make [target]\n\nSee STARTING_GUIDE.md for more info.\n\n"; \
-		   for (sort keys %help) { \
-			   print "${WHITE}$$_:${RESET}\n"; \
-			   for (@{$$help{$$_}}) { \
-				   $$sep = " " x (32 - length $$_->[0]); \
-				   print "  ${YELLOW}$$_->[0]${RESET}$$sep${GREEN}$$_->[1]${RESET}\n"; \
-			   }; \
-			   print "\n"; \
-		   }
+			 %help; \
+			 while(<>) { push @{$$help{$$2 // 'options'}}, [$$1, $$3] if /^([a-zA-Z\-]+)\s*:.*\#\#(?:@([a-zA-Z\-]+))?\s(.*)$$/ }; \
+			 print "Usage: make [target]\n\nSee STARTING_GUIDE.md for more info.\n\n"; \
+			 for (sort keys %help) { \
+				 print "${WHITE}$$_:${RESET}\n"; \
+				 for (@{$$help{$$_}}) { \
+					 $$sep = " " x (32 - length $$_->[0]); \
+					 print "  ${YELLOW}$$_->[0]${RESET}$$sep${GREEN}$$_->[1]${RESET}\n"; \
+				 }; \
+				 print "\n"; \
+			 }
 HOST_OS := $(shell uname | tr '[:upper:]' '[:lower:]')
 
 # This can come from Jenkins
@@ -307,6 +307,7 @@ lint: ##@test Run code style checks
 	clj-kondo --config .clj-kondo/config.edn --cache false --lint src && \
 	ALL_CLOJURE_FILES=$(call find_all_clojure_files) && \
 	zprint '{:search-config? true}' -sfc $$ALL_CLOJURE_FILES && \
+	sh scripts/lint-trailing-newline.sh && \
 	yarn prettier
 
 # NOTE: We run the linter twice because of https://github.com/kkinnear/zprint/issues/271
@@ -315,9 +316,9 @@ lint-fix: ##@test Run code style checks and fix issues
 	ALL_CLOJURE_FILES=$(call find_all_clojure_files) && \
 	zprint '{:search-config? true}' -sw $$ALL_CLOJURE_FILES && \
 	zprint '{:search-config? true}' -sw $$ALL_CLOJURE_FILES && \
+	sh scripts/lint-trailing-newline.sh --fix && \
 	yarn prettier
 
-
 shadow-server: export TARGET := clojure
 shadow-server:##@ Start shadow-cljs in server mode for watching
 	yarn shadow-cljs server

scripts/lint-trailing-newline.sh

@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+
+set -eof pipefail
+
+FILES=$(comm -23 <(sort <(git ls-files --cached --others --exclude-standard)) <(sort <(git ls-files --deleted)) | grep --ignore-case -E '\.(java|cpp|nix|json|sh|md|js|clj|cljs|cljc|edn)$')
+N_FILES=$(echo "$FILES" | wc -l)
+LINT_SHOULD_FIX=0
+
+if [[ -n $1 && $1 != '--fix' ]]; then
+    echo "Unknown option '$1'" >&2
+    exit 1
+elif [[ $1 == '--fix' ]]; then
+    LINT_SHOULD_FIX=1
+fi
+
+echo "Checking ${N_FILES} files for missing trailing newlines."
+
+# Do not process the whole file and only check the last character. Ignore empty
+# files. Taken from https://stackoverflow.com/a/10082466.
+for file in $FILES; do
+    if [ -s "$file" ] && [ "$(tail -c1 "$file"; echo x)" != $'\nx' ]; then
+        if [[ $LINT_SHOULD_FIX -eq 1 ]]; then
+            echo "" >>"$file"
+        else
+            LINT_ERROR=1
+            echo "No trailing newline: $file" >&2
+        fi
+    fi
+done
+
+if [[ $LINT_ERROR -eq 1 ]]; then
+    exit 1
+fi