Initial reorg.

This is largely the same as #305, but updated for the current tree.

crates/wasi-common/wig/src/utils.rs

@@ -0,0 +1,54 @@
+use proc_macro2::{Literal, TokenStream, TokenTree};
+/// Given the input tokens to a macro invocation, return the path to the
+/// witx file to process.
+pub(crate) fn witx_path_from_args(args: TokenStream) -> (String, String) {
+    let mut strings = Vec::new();
+
+    for arg in args {
+        if let TokenTree::Literal(literal) = arg {
+            let parsed = parse_string_literal(literal);
+
+            strings.push(parsed);
+        } else {
+            panic!("arguments must be string literals");
+        }
+    }
+
+    if strings.len() != 2 {
+        panic!("expected two string literals");
+    }
+
+    let phase = &strings[0];
+    let id = &strings[1];
+    let path = witx_path(phase, id);
+
+    (path, phase.clone())
+}
+
+fn witx_path(phase: &str, id: &str) -> String {
+    let root = std::env::var("CARGO_MANIFEST_DIR").unwrap_or(".".into());
+    format!("{}/WASI/phases/{}/witx/{}.witx", root, phase, id)
+}
+
+// Convert a `Literal` holding a string literal into the `String`.
+//
+// FIXME: It feels like there should be an easier way to do this.
+fn parse_string_literal(literal: Literal) -> String {
+    let s = literal.to_string();
+    assert!(
+        s.starts_with('"') && s.ends_with('"'),
+        "string literal must be enclosed in double-quotes"
+    );
+
+    let trimmed = s[1..s.len() - 1].to_owned();
+    assert!(
+        !trimmed.contains('"'),
+        "string literal must not contain embedded quotes for now"
+    );
+    assert!(
+        !trimmed.contains('\\'),
+        "string literal must not contain embedded backslashes for now"
+    );
+
+    trimmed
+}