cli: default naming, default string encoding flags (#399)

* cli: default naming, default string encoding flags

* default c to utf8

* use stringencoding default, only infer name for default flag

Author: Guy Bedford

crates/gen-guest-c/src/lib.rs

@@ -31,7 +31,7 @@ pub struct Opts {
     #[cfg_attr(feature = "clap", arg(long))]
     pub no_helpers: bool,
     /// Set component string encoding
-    #[cfg_attr(feature = "clap", arg(long))]
+    #[cfg_attr(feature = "clap", arg(long, default_value_t = StringEncoding::default()))]
     pub string_encoding: StringEncoding,
 }
 

crates/wit-component/src/lib.rs

@@ -3,6 +3,7 @@
 #![deny(missing_docs)]
 
 use anyhow::{bail, Result};
+use std::fmt::Display;
 use std::str::FromStr;
 use wasm_encoder::CanonicalOption;
 
@@ -37,6 +38,16 @@ impl Default for StringEncoding {
     }
 }
 
+impl Display for StringEncoding {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            StringEncoding::UTF8 => write!(f, "utf8"),
+            StringEncoding::UTF16 => write!(f, "utf16"),
+            StringEncoding::CompactUTF16 => write!(f, "compact-utf16"),
+        }
+    }
+}
+
 impl FromStr for StringEncoding {
     type Err = anyhow::Error;
 

src/bin/wit-bindgen.rs

@@ -126,7 +126,7 @@ struct World {
     /// The top-level name of the generated bindings, which may be used for
     /// naming modules/files/etc.
     #[clap(long, short)]
-    name: String,
+    name: Option<String>,
 }
 
 fn parse_named_interface(s: &str) -> Result<Interface> {
@@ -283,7 +283,19 @@ fn gen_world(
         exports,
         default: world.default,
     };
-    generator.generate(&world.name, &interfaces, files);
+    let name = match &world.name {
+        Some(name) => name,
+        None => {
+            if let Some(default) = &interfaces.default {
+                &default.name
+            } else {
+                return Err(anyhow!(
+                    "--name flag is required unless setting the interface via --default"
+                ));
+            }
+        }
+    };
+    generator.generate(name, &interfaces, files);
     Ok(())
 }