add --list-fetchers and --list-possible-fetchers

src/cli.rs

@@ -7,9 +7,19 @@ use url::Url;
 #[command(version, verbatim_doc_comment)]
 pub struct Opts {
     /// URL to the repository to be fetched
+    #[arg(
+        required_unless_present = "command",
+        default_value = "x:", // placeholder value, will not be accessed
+        hide_default_value = true
+    )]
     pub url: Url,
 
     /// the revision or reference to be fetched
+    #[arg(
+        required_unless_present = "command",
+        default_value_t,
+        hide_default_value = true
+    )]
     pub rev: String,
 
     /// specify the fetcher function instead of inferring from the URL
@@ -23,6 +33,14 @@ pub struct Opts {
     /// output in json format
     #[arg(short, long)]
     pub json: bool,
+
+    /// List all available fetchers
+    #[arg(short, long, group = "command")]
+    pub list_fetchers: bool,
+
+    /// List all fetchers that can be generated without --fetcher
+    #[arg(short = 'L', long, group = "command")]
+    pub list_possible_fetchers: bool,
 }
 
 #[derive(Clone, Debug, ValueEnum)]

src/main.rs

@@ -2,7 +2,7 @@ mod cli;
 mod fetcher;
 
 use anyhow::{bail, Result};
-use clap::Parser;
+use clap::{Parser, ValueEnum};
 use url::Host;
 
 use crate::{
@@ -13,11 +13,24 @@ use crate::{
     },
 };
 
-use std::io::stdout;
+use std::io::{stdout, Write};
 
 fn main() -> Result<()> {
     let opts = Opts::parse();
 
+    if opts.list_fetchers || opts.list_possible_fetchers {
+        let mut out = stdout().lock();
+        for fetcher in FetcherFunction::value_variants() {
+            if matches!(fetcher, FetcherFunction::Fetchhg) && opts.list_possible_fetchers {
+                continue;
+            }
+            if let Some(fetcher) = fetcher.to_possible_value() {
+                writeln!(out, "{}", fetcher.get_name())?;
+            }
+        }
+        return Ok(());
+    }
+
     let fetcher: FetcherDispatch = match (opts.fetcher, opts.url.host()) {
         (None | Some(FetcherFunction::FetchFromGitHub), Some(Host::Domain("github.com"))) => {
             FetchFromGitHub(None).into()