add --parse

src/cli.rs

@@ -33,6 +33,12 @@ pub struct Opts {
     #[arg(short, long, group = "format")]
     pub json: bool,
 
+    /// parse the url without fetching the hash, similar to --json
+    ///
+    /// note that --arg(-str) and --overwrite(-str) will be ignored silently
+    #[arg(short, long, group = "format")]
+    pub parse: bool,
+
     /// additional arguments to pass to the fetcher
     #[arg(short, long = "arg", num_args = 2, value_names = ["NAME", "EXPR"])]
     pub args: Vec<String>,

src/fetcher/mod.rs

@@ -59,6 +59,13 @@ pub trait Fetcher<'a> {
         overwrites: Vec<(String, String)>,
         overwrites_str: Vec<(String, String)>,
     ) -> Result<()>;
+
+    fn to_json(
+        &'a self,
+        out: &mut impl ::std::io::Write,
+        url: &'a ::url::Url,
+        rev: Option<String>,
+    ) -> ::anyhow::Result<()>;
 }
 
 #[enum_dispatch(Fetcher)]
@@ -164,6 +171,42 @@ macro_rules! impl_fetcher {
                     overwrites_str,
                 )
             }
+
+            fn to_json(
+                &'a self,
+                out: &mut impl ::std::io::Write,
+                url: &'a ::url::Url,
+                rev: Option<String>,
+            ) -> ::anyhow::Result<()> {
+                use anyhow::Context;
+                use serde_json::{json, Value};
+
+                let values = self
+                    .get_values(url)
+                    .with_context(|| format!("failed to parse {url}"))?;
+
+                let mut fetcher_args = Value::from_iter(Self::KEYS.into_iter().zip(values));
+
+                if let Some(host) = self.host() {
+                    fetcher_args[Self::HOST_KEY] = json!(host);
+                }
+                if let Some(group) = self.group() {
+                    fetcher_args["group"] = json!(group);
+                }
+                if let Some(rev) = rev {
+                    fetcher_args["rev"] = json!(rev);
+                }
+
+                serde_json::to_writer(
+                    out,
+                    &json!({
+                        "fetcher": Self::NAME,
+                        "args": fetcher_args,
+                    }),
+                )?;
+
+                Ok(())
+            }
         }
     };
 }

src/main.rs

@@ -152,6 +152,8 @@ fn main() -> Result<()> {
             opts.overwrites.into_iter().tuples().collect(),
             opts.overwrites_str.into_iter().tuples().collect(),
         )
+    } else if opts.parse {
+        fetcher.to_json(out, &opts.url, opts.rev)
     } else {
         let mut overwrites: FxHashMap<_, _> = opts.overwrites.into_iter().tuples().collect();
 

tests/cmd/parse.stdout

@@ -0,0 +1 @@
+{"args":{"owner":"nix-community","repo":"nurl","rev":"v0.3.0"},"fetcher":"fetchFromGitHub"}

tests/cmd/parse.toml

@@ -0,0 +1 @@
+args = ["https://github.com/nix-community/nurl", "v0.3.0", "--parse"]

tests/integration.rs

@@ -23,7 +23,7 @@ fn verify_outputs() {
             .strip_suffix(".stdout")
             .unwrap();
 
-        if matches!(name, "hash" | "json") {
+        if matches!(name, "hash" | "json" | "parse") {
             eprintln!("skipping {}", path.display());
             continue;
         }