[Incremental compiler] Only re-check package-uris if base-uri changed

When the .packages file has changed we need to re-check all package-uris
to see if we need to invalidate the builders (if the file uri for a
package uri library (e.g. if the package was upgrade) has changed we
have to invalidate it).
This translation is semi-expensive though, so if we can avoid it that
would be a good thing.

This CL caches the "base URI" for packages from the previous run,
so we can start by comparing the base-URIs: If the base-uri for a
specific package hasn't changed, nor will the actual translation.
Only if the base uri has changed we do the actual translation,
and thus save many package-to-file-uri translations.

An internal benchmark via kernel worker of lots of outline
calculations in worker mode with reuse and the incremental compiler
(where the .packages file change every time and we have lots of
package-uri libraries) goes from ~185 seconds to ~162 seconds.

Change-Id: I3ed48b23a590dbf66f8a2379bb88e1b177f1f034
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/103804
Reviewed-by: Kevin Millikin <[email protected]>

Author: jensjoha

pkg/front_end/lib/src/fasta/incremental_compiler.dart

@@ -96,6 +96,8 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
   final Component componentToInitializeFrom;
   bool initializedFromDill = false;
   Uri previousPackagesUri;
+  Map<String, Uri> previousPackagesMap;
+  Map<String, Uri> currentPackagesMap;
   bool hasToCheckPackageUris = false;
   Map<Uri, List<DiagnosticMessageFromJson>> remainingComponentProblems =
       new Map<Uri, List<DiagnosticMessageFromJson>>();
@@ -137,6 +139,8 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
       hasToCheckPackageUris = hasToCheckPackageUris || bypassCache;
       UriTranslator uriTranslator =
           await c.options.getUriTranslator(bypassCache: bypassCache);
+      previousPackagesMap = currentPackagesMap;
+      currentPackagesMap = uriTranslator.packages.asMap();
       ticker.logMs("Read packages file");
 
       if (dillLoadedData == null) {
@@ -831,10 +835,21 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
       if (importUri != fileUri && invalidatedUris.contains(fileUri)) {
         return true;
       }
-      if (hasToCheckPackageUris &&
-          importUri.scheme == "package" &&
-          uriTranslator.translate(importUri, false) != fileUri) {
-        return true;
+      if (hasToCheckPackageUris && importUri.scheme == "package") {
+        // Get package name, check if the base URI has changed for the package,
+        // if it has, translate the URI again,
+        // otherwise the URI cannot have changed.
+        String path = importUri.path;
+        int firstSlash = path.indexOf('/');
+        String packageName = path.substring(0, firstSlash);
+        if (previousPackagesMap == null ||
+            (previousPackagesMap[packageName] !=
+                currentPackagesMap[packageName])) {
+          Uri newFileUri = uriTranslator.translate(importUri, false);
+          if (newFileUri != fileUri) {
+            return true;
+          }
+        }
       }
       if (builders[importUri]?.isSynthetic ?? false) return true;
       return false;