vdoc: fix panic on empty `//` comment on `v doc -f html file.v`; turn `expected code block after empty example` to a warning

cmd/tools/vdoc/html.v

@@ -303,7 +303,7 @@ fn html_highlight(code string, tb &ast.Table) string {
 		} else if typ == .char {
 			'`$tok.lit`'
 		} else if typ == .comment {
-			if tok.lit[0] == 1 { '//${tok.lit[1..]}' } else { '//$tok.lit' }
+			if tok.lit != '' && tok.lit[0] == 1 { '//${tok.lit[1..]}' } else { '//$tok.lit' }
 		} else {
 			tok.lit
 		}

cmd/tools/vdoc/tests/testdata/basic/main.comments.out

@@ -1,7 +1,13 @@
 module main
 
 const (
-	source_root = 'temp'
+	source_root = 'temp' // some const
+	another     = int(5) //
 )
+const (
+	windowpos_undefined_mask = C.SDL_WINDOWPOS_UNDEFINED_MASK //   0x1FFF0000u
+	windowpos_undefined      = C.SDL_WINDOWPOS_UNDEFINED //
+)
+    Used to indicate that you don't care what the window position is.
 fn funky()
     funky - comment for function below

cmd/tools/vdoc/tests/testdata/basic/main.out

@@ -1,6 +1,11 @@
 module main
 
 const (
-	source_root = 'temp'
+	source_root = 'temp' // some const
+	another     = int(5) //
+)
+const (
+	windowpos_undefined_mask = C.SDL_WINDOWPOS_UNDEFINED_MASK //   0x1FFF0000u
+	windowpos_undefined      = C.SDL_WINDOWPOS_UNDEFINED //
 )
 fn funky()

cmd/tools/vdoc/tests/testdata/basic/main.v

@@ -1,5 +1,12 @@
 pub const (
-	source_root = 'temp'
+	source_root = 'temp' // some const
+	another     = int(5) //
+)
+
+// Used to indicate that you don't care what the window position is.
+pub const (
+	windowpos_undefined_mask = C.SDL_WINDOWPOS_UNDEFINED_MASK //   0x1FFF0000u
+	windowpos_undefined      = C.SDL_WINDOWPOS_UNDEFINED //
 )
 
 // funky - comment for function below

cmd/tools/vdoc/utils.v

@@ -162,7 +162,11 @@ fn color_highlight(code string, tb &ast.Table) string {
 				lit = term.yellow('`$tok.lit`')
 			}
 			.comment {
-				lit = if tok.lit[0] == 1 { '//${tok.lit[1..]}' } else { '//$tok.lit' }
+				lit = if tok.lit != '' && tok.lit[0] == 1 {
+					'//${tok.lit[1..]}'
+				} else {
+					'//$tok.lit'
+				}
 			}
 			.keyword {
 				lit = term.bright_blue(tok.lit)
@@ -209,16 +213,18 @@ fn color_highlight(code string, tb &ast.Table) string {
 					} else if
 						next_tok.kind in [.lcbr, .rpar, .eof, .comma, .pipe, .name, .rcbr, .assign, .key_pub, .key_mut, .pipe, .comma]
 						&& prev.kind in [.name, .amp, .rsbr, .key_type, .assign, .dot, .question, .rpar, .key_struct, .key_enum, .pipe, .key_interface]
-						&& (tok.lit[0].is_capital() || prev_prev.lit in ['C', 'JS']) {
+						&& ((tok.lit != '' && tok.lit[0].is_capital())
+						|| prev_prev.lit in ['C', 'JS']) {
 						tok_typ = .symbol
-					} else if next_tok.kind == .lpar || (!tok.lit[0].is_capital()
+					} else if next_tok.kind == .lpar
-						&& next_tok.kind == .lt && next_tok.pos == tok.pos + tok.lit.len) {
+						|| (!(tok.lit != '' && tok.lit[0].is_capital()) && next_tok.kind == .lt
+						&& next_tok.pos == tok.pos + tok.lit.len) {
 						tok_typ = .function
 					} else if next_tok.kind == .dot {
 						if tok.lit in ['C', 'JS'] {
 							tok_typ = .prefix
 						} else {
-							if tok.lit[0].is_capital() {
+							if tok.lit != '' && tok.lit[0].is_capital() {
 								tok_typ = .symbol
 							} else {
 								tok_typ = .module_

vlib/v/doc/node.v

@@ -62,13 +62,12 @@ pub fn (dc DocNode) merge_comments_without_examples() string {
 		if dc.comments[i].is_multi_line_example() {
 			i++
 			if i == dc.comments.len || !dc.comments[i].has_triple_backtick() {
-				eprintln('$dc.file_path:$dc.pos.line_nr: Expected code block after empty example line:')
+				eprintln('$dc.file_path:$dc.pos.line_nr: warning: expected code block after empty example line:')
 				eprintln('// ```')
 				if i < dc.comments.len {
 					eprintln('Found:')
 					eprintln('//' + dc.comments[i].text[1..])
 				}
-				exit(1)
 			}
 			i++
 			for i < dc.comments.len && !dc.comments[i].has_triple_backtick() {