flag: fix rendering bug, make newline logic/code more readable and clean (#21896)

vlib/flag/flag_to_doc_test.v

@@ -70,3 +70,126 @@ fn test_attrs_override() {
 		description: 'My application'
 	)! == doc3
 }
+
+const doc4 = 'flag_to_doc_test 1.0
+--------------------------------------------------------------------------------
+Flag to doc test.
+Content here
+
+Options:
+  -v, --show-version        Show version and exit
+
+  -d, --debug <int>         Debug level
+
+  -l <f32>                  Level of lorem ipsum
+                            and more
+                            many many many more.
+                            Notice how user newlines/format is kept since
+                            input lines are all less or within
+                            the default layout.description_padding
+                            and max width
+
+  --example <string>        Looong example text without newlines or anything
+                            else and lorem ipsum and more and many many many
+                            more. Should be auto fitted
+
+  --square
+
+  -m, -mmm... (can repeat)  This flag can be repeated
+
+  -w, --wroom <int> (allowed multiple times)
+
+  --the-limit <string>      Looongbobbytextwithoutnewlinesoranythingelseandlorem
+                            ipsumandmoreandmanymanymanymore
+                            ffffffffffffffffffffffffffffffff f
+
+  -e, --extra               Secret flag that does not exist on the struct,
+                            but we want documented (in same format as the
+                            others)
+
+  -q, --quiet-and-quite-long-flag <string>
+                            Mega long description and secret flag that does
+                            not exist on the struct, but we want documented.
+                            Also the flag has custom newlines and the flag
+                            line itself is super long
+
+Footer content'
+
+const doc5 = 'flag_to_doc_test 1.0
+--------------------------------------------------------------------------------
+Flag to doc test.
+Content here
+
+Options:
+  -v, --show-version        Show version and exit
+  -d, --debug <int>         Debug level
+  -l <f32>                  Level of lorem ipsum
+                            and more
+                            many many many more.
+                            Notice how user newlines/format is kept since
+                            input lines are all less or within
+                            the default layout.description_padding
+                            and max width
+  --example <string>        Looong example text without newlines or anything
+                            else and lorem ipsum and more and many many many
+                            more. Should be auto fitted
+  --square
+  -m, -mmm... (can repeat)  This flag can be repeated
+  -w, --wroom <int> (allowed multiple times)
+  --the-limit <string>      Looongbobbytextwithoutnewlinesoranythingelseandlorem
+                            ipsumandmoreandmanymanymanymore
+                            ffffffffffffffffffffffffffffffff f
+  -e, --extra               Secret flag that does not exist on the struct,
+                            but we want documented (in same format as the
+                            others)
+  -q, --quiet-and-quite-long-flag <string>
+                            Mega long description and secret flag that does
+                            not exist on the struct, but we want documented.
+                            Also the flag has custom newlines and the flag
+                            line itself is super long
+
+Footer content'
+
+@[name: 'flag_to_doc_test']
+@[version: '1.0']
+struct DocTest {
+	show_version bool   @[short: v; xdoc: 'Show version and exit']
+	debug_level  int    @[long: debug; short: d; xdoc: 'Debug level']
+	level        f32    @[only: l; xdoc: 'Override this doc string']
+	example      string
+	square       bool
+	multi        int    @[only: m; repeats]
+	wroom        []int  @[short: w]
+	the_limit    string
+}
+
+const field_docs = {
+	'level':                                    'Level of lorem ipsum\nand more\nmany many many more.\nNotice how user newlines/format is kept since\ninput lines are all less or within\nthe default layout.description_padding\nand max width'
+	'example':                                  'Looong example text without newlines or anything else and lorem ipsum and more and many many many more. Should be auto fitted'
+	'the_limit':                                'Looongbobbytextwithoutnewlinesoranythingelseandlorem ipsumandmoreandmanymanymanymore ffffffffffffffffffffffffffffffff f'
+	'multi':                                    'This flag can be repeated'
+	'-e, --extra':                              'Secret flag that does not exist on the struct, but we want documented (in same format as the others)'
+	'-q, --quiet-and-quite-long-flag <string>': 'Mega long description and secret flag that does not exist on the struct, but we want documented. Also the flag has custom newlines\nand the flag line itself is super long'
+}
+
+fn test_flag_to_doc_spacing_and_new_lines() {
+	assert flag.to_doc[DocTest](
+		description: 'Flag to doc test.
+Content here'
+		footer: '
+Footer content'
+		fields: unsafe { field_docs }
+	)! == doc4
+
+	// Test in compact mode also
+	assert flag.to_doc[DocTest](
+		options: flag.DocOptions{
+			compact: true
+		}
+		description: 'Flag to doc test.
+Content here'
+		footer: '
+Footer content'
+		fields: unsafe { field_docs }
+	)! == doc5
+}