Bring back generation of help strings from DISPLAY chunks constant

This is done by extracting such a constant to a separate module file,
outside of `StripChunks`.

src/cli.rs

@@ -1,6 +1,9 @@
-use clap::{value_parser, Arg, ArgAction, Command};
 use std::path::PathBuf;
 
+use clap::{value_parser, Arg, ArgAction, Command};
+
+include!("display_chunks.rs");
+
 pub fn build_command() -> Command {
     // Note: clap 'wrap_help' is enabled to automatically wrap lines according to terminal width.
     // To keep things tidy though, short help descriptions should be no more than 54 characters,
@@ -118,18 +121,23 @@ Note that this will not preserve the directory structure of the input files when
         .arg(
             Arg::new("strip")
                 .help("Strip metadata (safe, all, or comma-separated list)\nCAUTION: 'all' will convert APNGs to standard PNGs")
-                .long_help("\
+                .long_help(format!("\
 Strip metadata chunks, where <mode> is one of:
 
     safe    =>  Strip all non-critical chunks, except for the following:
-                    cICP, iCCP, sRGB, pHYs, acTL, fcTL, fdAT
+                    {}
     all     =>  Strip all non-critical chunks
     <list>  =>  Strip chunks in the comma-separated list, e.g. 'bKGD,cHRM'
 
 CAUTION: 'all' will convert APNGs to standard PNGs.
 
 Note that 'bKGD', 'sBIT' and 'hIST' will be forcibly stripped if the color type or bit \
-depth is changed, regardless of any options set.")
+depth is changed, regardless of any options set.",
+                       DISPLAY_CHUNKS
+                           .iter()
+                           .map(|c| String::from_utf8_lossy(c))
+                           .collect::<Vec<_>>()
+                           .join(", ")))
                 .long("strip")
                 .value_name("mode")
                 .conflicts_with("strip-safe"),

src/display_chunks.rs

@@ -0,0 +1,4 @@
+/// List of chunks that affect image display and will be kept when using the `Safe` chunk strip option
+pub const DISPLAY_CHUNKS: [[u8; 4]; 7] = [
+    *b"cICP", *b"iCCP", *b"sRGB", *b"pHYs", *b"acTL", *b"fcTL", *b"fdAT",
+];

src/headers.rs

@@ -5,6 +5,7 @@ use rgb::{RGB16, RGBA8};
 use crate::{
     colors::{BitDepth, ColorType},
     deflate::{crc32, inflate},
+    display_chunks::DISPLAY_CHUNKS,
     error::PngError,
     interlace::Interlacing,
     AtomicMin, Deflaters, PngResult,
@@ -86,18 +87,12 @@ pub enum StripChunks {
 }
 
 impl StripChunks {
-    /// List of chunks that affect image display and will be kept when using the `Safe` option
-    // NOTE: If this list is updated, the documentation in `cli` must also be updated
-    pub const DISPLAY: [[u8; 4]; 7] = [
-        *b"cICP", *b"iCCP", *b"sRGB", *b"pHYs", *b"acTL", *b"fcTL", *b"fdAT",
-    ];
-
     pub(crate) fn keep(&self, name: &[u8; 4]) -> bool {
         match &self {
             StripChunks::None => true,
             StripChunks::Keep(names) => names.contains(name),
             StripChunks::Strip(names) => !names.contains(name),
-            StripChunks::Safe => Self::DISPLAY.contains(name),
+            StripChunks::Safe => DISPLAY_CHUNKS.contains(name),
             StripChunks::All => false,
         }
     }

src/lib.rs

@@ -62,6 +62,7 @@ pub use crate::{
 mod atomicmin;
 mod colors;
 mod deflate;
+mod display_chunks;
 mod error;
 mod evaluate;
 mod filters;

src/main.rs

@@ -27,6 +27,8 @@ use log::{error, warn, Level, LevelFilter};
 use oxipng::{Deflaters, InFile, Options, OutFile, RowFilter, StripChunks};
 use rayon::prelude::*;
 
+use crate::cli::DISPLAY_CHUNKS;
+
 fn main() {
     let matches = cli::build_command()
         // Set the value parser for filters which isn't appropriate to do in the build_command function
@@ -281,7 +283,7 @@ fn parse_opts_into_struct(
             })
             .collect::<Result<IndexSet<_>, _>>()?;
         if keep_display {
-            names.extend(StripChunks::DISPLAY.iter().cloned());
+            names.extend(DISPLAY_CHUNKS.iter().cloned());
         }
         opts.strip = StripChunks::Keep(names)
     }