only use worlds from componentize-go.toml files when not specified via CLI

Previously, we'd union all the worlds specified via the CLI _and_ via
`componentize-go.toml` files, but that can get very confusing for the user.  Now
we'll only use the toml file ones as a default if none are specified via the
CLI.

Author: dicej

src/command.rs

@@ -42,10 +42,11 @@ pub struct WitOpts {
     /// This may be specified more than once, in which case the worlds will be
     /// merged.
     ///
-    /// Note that, unless `--ignore-toml-files` is specified, `componentize-go`
-    /// will also use `go list` to scan the current Go module and its
-    /// dependencies to find any `componentize-go.toml` files.  The WIT worlds
-    /// referenced by any such files will be added to this list automatically.
+    /// Note that, unless `--ignore-toml-files` _or_ at least one `--world`
+    /// option is specified, `componentize-go` will use `go list` to scan the
+    /// current Go module and its dependencies to find any
+    /// `componentize-go.toml` files, and the WIT worlds referenced by any such
+    /// files will be used.
     #[arg(long, short = 'w')]
     pub world: Vec<String>,
 

src/utils.rs

@@ -108,6 +108,9 @@ fn maybe_add_dependencies(
         .map(|v| PathBuf::from(v.as_ref()))
         .collect::<BTreeSet<_>>();
     let mut worlds = worlds.iter().cloned().collect::<BTreeSet<_>>();
+    // Only add worlds from `componentize-go.toml` files if none were specified
+    // explicitly via the CLI:
+    let add_worlds = worlds.is_empty();
 
     if !ignore_toml_files && Path::new("go.mod").exists() {
         let mut command = std::process::Command::new("go");
@@ -133,7 +136,9 @@ fn maybe_add_dependencies(
             let module = PathBuf::from(module);
             if let Ok(manifest) = std::fs::read_to_string(module.join("componentize-go.toml")) {
                 let config = toml::from_str::<ComponentizeGoConfig>(&manifest)?;
-                worlds.extend(config.worlds);
+                if add_worlds {
+                    worlds.extend(config.worlds);
+                }
                 paths.extend(config.wit_paths.into_iter().map(|v| module.join(v)));
             }
         }