Fine. Update LinkedElementFactory.libraryOfUri() to return null for missing library.

We use this method to check requirements, and it is possible that some
libraries are not available anymore. Specifically, this happens when
conditional imports used, and environment variables changed.

There are no new tests, because test failures happened with existing
summary tests when `withFineDependencies` is `true`.

Change-Id: I460948a759be7ed8c5b36f76b61ab4e1d1522097
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/444520
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/summary2/linked_element_factory.dart

@@ -96,37 +96,6 @@ class LinkedElementFactory {
     return Namespace(exportedNames);
   }
 
-  LibraryElementImpl createLibraryElementForReading(Uri uri) {
-    var sourceFactory = analysisContext.sourceFactory;
-    var librarySource = sourceFactory.forUri2(uri)!;
-
-    var reader = _libraryReaders[uri];
-    if (reader == null) {
-      var rootChildren = rootReference.children.map((e) => e.name).toList();
-      if (rootChildren.length > 50) {
-        rootChildren = [
-          ...rootChildren.take(50),
-          '... (${rootChildren.length} total)',
-        ];
-      }
-      var readers = _libraryReaders.keys.map((uri) => uri.toString()).toList();
-      if (readers.length > 50) {
-        readers = [...readers.take(50), '... (${readers.length} total)'];
-      }
-      throw ArgumentError(
-        'Missing library: $uri\n'
-        'Libraries: $uriListWithLibraryElements\n'
-        'Root children: $rootChildren\n'
-        'Readers: $readers\n'
-        'Log: ${_logRing.join('\n')}\n',
-      );
-    }
-
-    var libraryElement = reader.readElement(librarySource: librarySource);
-    setLibraryTypeSystem(libraryElement);
-    return libraryElement;
-  }
-
   void createTypeProviders(
     LibraryElementImpl dartCore,
     LibraryElementImpl dartAsync,
@@ -165,7 +134,9 @@ class LinkedElementFactory {
 
     if (reference.isLibrary) {
       var uri = uriCache.parse(reference.name);
-      return createLibraryElementForReading(uri);
+      var result = _createLibraryElementForReading(uri);
+      result ?? _reportMissingLibrary(uri);
+      return result;
     }
 
     var parentRef = reference.parentNotContainer;
@@ -191,15 +162,12 @@ class LinkedElementFactory {
     if (reference.element case LibraryElementImpl element) {
       return element;
     }
-    return createLibraryElementForReading(uri);
+    return _createLibraryElementForReading(uri);
   }
 
   LibraryElementImpl libraryOfUri2(Uri uri) {
     var element = libraryOfUri(uri);
-    if (element == null) {
-      libraryOfUri(uri);
-      throw StateError('No library: $uri');
-    }
+    element ?? _reportMissingLibrary(uri);
     return element;
   }
 
@@ -269,5 +237,43 @@ class LinkedElementFactory {
     libraryElement.hasTypeProviderSystemSet = true;
   }
 
+  LibraryElementImpl? _createLibraryElementForReading(Uri uri) {
+    var sourceFactory = analysisContext.sourceFactory;
+    var librarySource = sourceFactory.forUri2(uri);
+    if (librarySource == null) {
+      return null;
+    }
+
+    var reader = _libraryReaders[uri];
+    if (reader == null) {
+      return null;
+    }
+
+    var libraryElement = reader.readElement(librarySource: librarySource);
+    setLibraryTypeSystem(libraryElement);
+    return libraryElement;
+  }
+
   void _disposeLibrary(ElementImpl? libraryElement) {}
+
+  Never _reportMissingLibrary(Uri uri) {
+    var rootChildren = rootReference.children.map((e) => e.name).toList();
+    if (rootChildren.length > 50) {
+      rootChildren = [
+        ...rootChildren.take(50),
+        '... (${rootChildren.length} total)',
+      ];
+    }
+    var readers = _libraryReaders.keys.map((uri) => uri.toString()).toList();
+    if (readers.length > 50) {
+      readers = [...readers.take(50), '... (${readers.length} total)'];
+    }
+    throw ArgumentError(
+      'Missing library: $uri\n'
+      'Libraries: $uriListWithLibraryElements\n'
+      'Root children: $rootChildren\n'
+      'Readers: $readers\n'
+      'Log: ${_logRing.join('\n')}\n',
+    );
+  }
 }