Distinguish between cases "resolver doesn't exist" and "resolver does exist, but fails" when resolving logical locations

src/org/rascalmpl/library/lang/rascal/tests/library/IO.rsc

@@ -4,6 +4,79 @@ import IO;
 import DateTime;
 import String;
 
+test bool testLogicalLocationResolution() {
+    str scheme = "test-logical";
+
+    value exceptionOf(value() f) {
+        try {
+            f();
+            return "";
+        } catch e: {
+            return e;
+        }
+    }
+
+    bool throwsUnsupportedAuthority(value() f) {
+        return /Unsupported authority/ := "<exceptionOf(f)>";
+    }
+
+    bool throwsExceptionDownstream(value() f) {
+        return str s := "<exceptionOf(f)>" && "" != s && /Unsupported authority/ !:= s;
+    }
+
+    try {
+        // Register authorities `foo` and `bar`
+        registerLocations(scheme, "foo", (
+            |<scheme>://foo/|: |file:///|,
+            |<scheme>://foo/x/y/z|: |file:///x/y/z|
+        ));
+        registerLocations(scheme, "bar", (
+            |<scheme>://bar/|: |<scheme>://foo/|,
+            |<scheme>://bar/x/y/z|: |<scheme>://foo/x/y/z|
+        ));
+
+        assert lastModified(|<scheme>://foo/|) == lastModified(|file:///|) : "Resolution unexpectedly failed";
+        assert lastModified(|<scheme>://bar/|) == lastModified(|file:///|) : "Resolution unexpectedly failed";
+
+        str cause = "Resolution either unexpectedly succeeded or failed with an unexpected exception";
+        assert throwsExceptionDownstream(value() { return lastModified(|<scheme>://foo/x/y/z|); }) : cause;
+        assert throwsExceptionDownstream(value() { return lastModified(|<scheme>://bar/x/y/z|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>://baz/|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>://baz/x/y/z|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>://qux/|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>://qux/x/y/z|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>:///|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>:///x/y/z|); }) : cause;
+
+        // Register default authority
+        registerLocations(scheme, "", (
+            |<scheme>://baz/|: |<scheme>://bar/|,
+            |<scheme>://baz/x/y/z|: |<scheme>://bar/x/y/z|
+        ));
+
+        assert lastModified(|<scheme>://foo/|) == lastModified(|file:///|) : "Resolution unexpectedly failed";
+        assert lastModified(|<scheme>://bar/|) == lastModified(|file:///|) : "Resolution unexpectedly failed";
+        assert lastModified(|<scheme>://baz/|) == lastModified(|file:///|) : "Resolution unexpectedly failed";
+
+        assert throwsExceptionDownstream(value() { return lastModified(|<scheme>://foo/x/y/z|); }) : cause;
+        assert throwsExceptionDownstream(value() { return lastModified(|<scheme>://bar/x/y/z|); }) : cause;
+        assert throwsExceptionDownstream(value() { return lastModified(|<scheme>://baz/x/y/z|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>://qux/|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>://qux/x/y/z|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>:///|); }) : cause;
+        assert throwsUnsupportedAuthority(value() { return lastModified(|<scheme>:///x/y/z|); }) : cause;
+
+        return true;
+    }
+    catch false: // Catch block only to make finally block grammatical
+        throw false;
+    finally  {
+        unregisterLocations(scheme, "foo");
+        unregisterLocations(scheme, "bar");
+        unregisterLocations(scheme, "");
+    }
+}
+
 test bool testFileCopyCompletely() {
     writeFile(|tmp:///longFile|, "123456789");
     writeFile(|tmp:///shortFile|, "321");
@@ -22,9 +95,9 @@ test bool testFileCopyRecursive() {
 
 test bool watchDoesNotCrashOnURIRewrites() {
     writeFile(|tmp:///watchDoesNotCrashOnURIRewrites/someFile.txt|, "123456789");
-    watch(|tmp:///watchDoesNotCrashOnURIRewrites|, true, void (FileSystemChange event) { 
+    watch(|tmp:///watchDoesNotCrashOnURIRewrites|, true, void (FileSystemChange event) {
         // this should trigger the failing test finally
-        remove(event.file); 
+        remove(event.file);
     });
     return true;
 }
@@ -75,4 +148,4 @@ test bool renameDirectory() {
     writeFile(|tmp:///Folder/hello.txt|, "Hello World!");
     rename(|tmp:///Folder|, |tmp:///RenamedFolder|);
     return readFile(|tmp:///RenamedFolder/hello.txt|) == "Hello World!";
-}
+}

src/org/rascalmpl/uri/ILogicalSourceLocationResolver.java

@@ -2,10 +2,32 @@
 
 import java.io.IOException;
 
+import org.checkerframework.checker.nullness.qual.Nullable;
+
 import io.usethesource.vallang.ISourceLocation;
 
+/**
+ * Resolver of logical locations with a certain {@link #scheme} and {@link #authority}. Implementations of this
+ * interface for non-empty authorities are <em>authority-specific resolvers</em>. Implementations for the distinguished
+ * empty authority are <em>default resolvers</em>. To resolve a logical location, first, an authority-specific resolver
+ * for the scheme is sought. If it doesn't exist, then the default resolver for the scheme is sought instead. If it
+ * doesn't exist either, then an exception is thrown. Note: If an authority-specific resolver does exist, but fails,
+ * then the default resolver will not be sought instead (i.e., the default resolver resembles the default case of a
+ * switch statement with non-fallthrough cases).
+ */
 public interface ILogicalSourceLocationResolver {
-	ISourceLocation resolve(ISourceLocation input) throws IOException;
+
+	/**
+	 * @return {@code null} only if the authority of {@code input} is not supported/covered by this resolver.
+	 * Non-{@code null} otherwise.
+	 */
+	@Nullable ISourceLocation resolve(ISourceLocation input) throws IOException;
+
 	String scheme();
+
+	/**
+	 * @return A non-empty string if this is an authority-specific resolver. The empty string if this is a default
+	 * resolver.
+	 */
 	String authority();
 }