tools: add cmd/tools/show_ancient_deprecations.v, to cleanup ancient functionality, deprecated over an year ago (#18946)

cmd/tools/show_ancient_deprecations.v

@@ -0,0 +1,72 @@
+import os
+import time
+
+struct Context {
+mut:
+	cut_time     time.Time
+	deprecations int
+}
+
+fn (mut ctx Context) analyze_line(line string, position_file string, position_line int) {
+	blame_for_time := os.execute('git blame -L${position_line} --porcelain -- ${position_file}')
+	if blame_for_time.exit_code != 0 {
+		return
+	}
+	ts := blame_for_time.output.all_after('committer-time').all_before('\n').trim_space().int()
+	t := time.unix(ts)
+	if ctx.cut_time < t {
+		println('>>> SKIPPING since t: ${t} > ${ctx.cut_time}, line: ${line}')
+		return
+	}
+	ctx.deprecations++
+	blame_for_context := os.execute('git blame -L${position_line},+5 -- ${position_file}')
+	context := blame_for_context.output.trim_space().split_into_lines()
+	println('${position_file}:${position_line}: deprecation: ${ctx.deprecations}, timestamp: ${ts} - ${t}')
+	for cline in context {
+		println('    ${cline}')
+	}
+}
+
+fn main() {
+	if os.args.len < 2 {
+		eprintln('Usage: v run cmd/tools/show_ancient_deprecations.v [DAYS]')
+		exit(1)
+	}
+	cut_months := os.args[1].int()
+	cut_time := time.now().add(-cut_months * 24 * time.hour)
+	mut ctx := Context{
+		cut_time: cut_time
+	}
+	println('> Deprecations that happened before ${cut_time}')
+	all_v_files := os.walk_ext('.', '.v')
+	for v_file in all_v_files {
+		if v_file == './vlib/v/fmt/tests/attrs_keep.vv' {
+			println('>>> SKIPPING deprecations attrs formatting test file ${v_file}')
+			continue
+		}
+		if v_file.starts_with('./vlib/v/checker/tests') && v_file.contains('deprec') {
+			println('>>> SKIPPING deprecations test file ${v_file}')
+			continue
+		}
+		file_content := os.read_file(v_file)!
+		if !file_content.contains('[deprecated') {
+			continue
+		}
+		lines := file_content.split_into_lines()
+		for line_num := lines.len - 1; line_num > 0; line_num-- {
+			line := lines[line_num]
+			mut is_deprecation_line := false
+			if line.contains('[deprecated:') {
+				is_deprecation_line = true
+			}
+			if line.contains('[deprecated]') {
+				is_deprecation_line = true
+			}
+			if !is_deprecation_line {
+				continue
+			}
+			ctx.analyze_line(line, v_file, line_num + 1)
+		}
+	}
+	println('> Summary: there were ${ctx.deprecations} deprecations found, done before ${cut_time}.')
+}