[cmd/mdatagen] Enforce tab indentation in Go template files

Add a check-template-tabs Makefile target and CI step that fails if any
.go.tmpl file under cmd/mdatagen or cmd/builder contains lines with
leading spaces. Convert the two remaining offending templates
(config_from_cfggen.go.tmpl and config_from_cfggen_test.go.tmpl) from
space to tab indentation.

Fixes #14698

Assisted-by: Claude Sonnet 4.6

Author: Goutham-Annem

.chloggen/fix-14698-check-template-tabs.yaml

@@ -0,0 +1,6 @@
+change_type: enhancement
+component: cmd/mdatagen
+note: Add CI check to ensure Go template files use tabs for indentation; fix remaining space-indented templates.
+issues: [14698]
+subtext:
+change_logs: [user]

.github/workflows/build-and-test.yml

@@ -163,6 +163,8 @@ jobs:
         run: |
           make generate-chloggen-components
           git diff --exit-code || (echo '.chloggen/config.yaml is out of date, please run "make generate-chloggen-components" and commit the changes.' && exit 1)
+      - name: check-template-tabs
+        run: make check-template-tabs
 
   unittest-matrix:
     strategy:

Makefile

@@ -402,6 +402,14 @@ mdatagen-test:
 	cd cmd/mdatagen && $(MAKE) fmt
 	cd cmd/mdatagen && $(GOCMD) test ./...
 
+.PHONY: check-template-tabs
+check-template-tabs:
+	@if grep -rqP "^ " cmd/mdatagen/internal/templates/*.go.tmpl cmd/builder/internal/builder/templates/*.go.tmpl; then \
+		echo "ERROR: Go template files must use tabs for indentation, not spaces."; \
+		grep -rPn "^ " cmd/mdatagen/internal/templates/*.go.tmpl cmd/builder/internal/builder/templates/*.go.tmpl; \
+		exit 1; \
+	fi
+
 GITHUBGEN_ARGS ?= -skipgithub
 GITHUBGEN := $(GO_TOOL) githubgen $(GITHUBGEN_ARGS)