wit-parser package not found: explain error better (#1875)

* wit-parser: provide more context in package not found error

* better error reports

Author: pchickey

crates/wit-parser/src/ast.rs

@@ -1,4 +1,4 @@
-use crate::{Error, UnresolvedPackageGroup};
+use crate::{Error, PackageNotFoundError, UnresolvedPackageGroup};
 use anyhow::{bail, Context, Result};
 use lex::{Span, Token, Tokenizer};
 use semver::Version;
@@ -1758,6 +1758,19 @@ impl SourceMap {
         if let Some(_) = err.downcast_mut::<Error>() {
             return Err(err);
         }
+        if let Some(notfound) = err.downcast_mut::<PackageNotFoundError>() {
+            if notfound.highlighted.is_none() {
+                let msg = self.highlight_err(
+                    notfound.span.start,
+                    Some(notfound.span.end),
+                    &format!("{notfound}"),
+                );
+                notfound.highlighted = Some(msg);
+            }
+        }
+        if let Some(_) = err.downcast_mut::<PackageNotFoundError>() {
+            return Err(err);
+        }
 
         if let Some(lex) = err.downcast_ref::<lex::Error>() {
             let pos = match lex {

crates/wit-parser/src/lib.rs

@@ -273,6 +273,52 @@ impl fmt::Display for Error {
 
 impl std::error::Error for Error {}
 
+#[derive(Debug)]
+struct PackageNotFoundError {
+    span: Span,
+    requested: PackageName,
+    known: Vec<PackageName>,
+    highlighted: Option<String>,
+}
+
+impl PackageNotFoundError {
+    pub fn new(span: Span, requested: PackageName, known: Vec<PackageName>) -> Self {
+        Self {
+            span,
+            requested,
+            known,
+            highlighted: None,
+        }
+    }
+}
+
+impl fmt::Display for PackageNotFoundError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if let Some(highlighted) = &self.highlighted {
+            return highlighted.fmt(f);
+        }
+        if self.known.is_empty() {
+            write!(
+                f,
+                "package '{}' not found. no known packages.",
+                self.requested
+            )?;
+        } else {
+            write!(
+                f,
+                "package '{}' not found. known packages:\n",
+                self.requested
+            )?;
+            for known in self.known.iter() {
+                write!(f, "    {known}\n")?;
+            }
+        }
+        Ok(())
+    }
+}
+
+impl std::error::Error for PackageNotFoundError {}
+
 impl UnresolvedPackageGroup {
     /// Parses the given string as a wit document.
     ///

crates/wit-parser/src/resolve.rs

@@ -18,9 +18,9 @@ use crate::ast::{parse_use_path, ParsedUsePath};
 use crate::serde_::{serialize_arena, serialize_id_map};
 use crate::{
     AstItem, Docs, Error, Function, FunctionKind, Handle, IncludeName, Interface, InterfaceId,
-    InterfaceSpan, Mangling, PackageName, Results, SourceMap, Stability, Type, TypeDef,
-    TypeDefKind, TypeId, TypeIdVisitor, TypeOwner, UnresolvedPackage, UnresolvedPackageGroup,
-    World, WorldId, WorldItem, WorldKey, WorldSpan,
+    InterfaceSpan, Mangling, PackageName, PackageNotFoundError, Results, SourceMap, Stability,
+    Type, TypeDef, TypeDefKind, TypeId, TypeIdVisitor, TypeOwner, UnresolvedPackage,
+    UnresolvedPackageGroup, World, WorldId, WorldItem, WorldKey, WorldSpan,
 };
 
 mod clone;
@@ -2846,7 +2846,13 @@ impl Remap {
                 .package_names
                 .get(pkg_name)
                 .copied()
-                .ok_or_else(|| Error::new(span, "package not found"))?;
+                .ok_or_else(|| {
+                    PackageNotFoundError::new(
+                        span,
+                        pkg_name.clone(),
+                        resolve.package_names.keys().cloned().collect(),
+                    )
+                })?;
 
             // Functions can't be imported so this should be empty.
             assert!(unresolved_iface.functions.is_empty());

crates/wit-parser/tests/ui/parse-fail/bad-pkg6.wit.result

@@ -1,4 +1,6 @@
-failed to resolve directory while parsing WIT for path [tests/ui/parse-fail/bad-pkg6]: package not found
+failed to resolve directory while parsing WIT for path [tests/ui/parse-fail/bad-pkg6]: package 'foo:bar' not found. known packages:
+    foo:baz
+
      --> tests/ui/parse-fail/bad-pkg6/root.wit:3:7
       |
     3 |   use foo:bar/baz.{};

crates/wit-parser/tests/ui/parse-fail/unresolved-interface4.wit.result

@@ -1,4 +1,4 @@
-package not found
+package 'some:dependency' not found. no known packages.
      --> tests/ui/parse-fail/unresolved-interface4.wit:6:10
       |
     6 |   import some:dependency/iface;