Backoff SourceExcerptProvider from attempting to get source code of stub files when reporting errors.

When JSCompiler generates an error report, it tries to format the error message with the relevant source code snippet. To do that, it relies on a SourceExcerptProvider to give it the relevant snippet. The implementation for this SourceExcerptProvider interface is provided by the compiler.

This CL makes the SourceExcerptProvider (i.e. the compiler implementing it) backoff when the source file is a stub source file.

The sequence of calls is:
`ThreadSafeDelegatingErrorManager.generateReport()` --> `BasicErrorManager.generateReport()` -->  .. --> `LightweightMessageFormatter.formatError()` --> `SourceExcerptProvider$SourceExcerpt$1.get()` --> `compiler.getSourceLine()`

Also adds a unit test to check that compiler reports an error without crashing.

Fixes the crash reported in b/379868495 synced to CL 697886232 - http://sponge2/4ea3023b-17f3-45b4-adb4-de5ce0d1e864

PiperOrigin-RevId: 698904429

Author: rishipal

src/com/google/javascript/jscomp/Compiler.java

@@ -3394,6 +3394,9 @@ public boolean hasErrors() {
 
   public @Nullable CharSequence getSourceFileContentByName(String sourceName) {
     SourceFile file = getSourceFileByName(sourceName);
+    if (file.isStubSourceFileForAlreadyProvidedInput()) {
+      return null;
+    }
     checkNotNull(file);
     try {
       return file.getCode();
@@ -3521,7 +3524,7 @@ private synchronized void addSourceMapSourceFiles(SourceMapInput inputSourceMap)
       return null;
     }
     SourceFile input = getSourceFileByName(sourceName);
-    if (input != null) {
+    if (input != null && !input.isStubSourceFileForAlreadyProvidedInput()) {
       return input.getLine(lineNumber);
     }
     return null;
@@ -3533,7 +3536,7 @@ private synchronized void addSourceMapSourceFiles(SourceMapInput inputSourceMap)
       return null;
     }
     SourceFile input = getSourceFileByName(sourceName);
-    if (input != null) {
+    if (input != null && !input.isStubSourceFileForAlreadyProvidedInput()) {
       return input.getLines(lineNumber, length);
     }
     return null;
@@ -3545,7 +3548,7 @@ private synchronized void addSourceMapSourceFiles(SourceMapInput inputSourceMap)
       return null;
     }
     SourceFile input = getSourceFileByName(sourceName);
-    if (input != null) {
+    if (input != null && !input.isStubSourceFileForAlreadyProvidedInput()) {
       return input.getRegion(lineNumber);
     }
     return null;

test/com/google/javascript/jscomp/integration/TypedAstIntegrationTest.java

@@ -51,6 +51,7 @@
 import java.nio.file.Path;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Objects;
 import java.util.zip.GZIPInputStream;
 import org.junit.Before;
 import org.junit.Test;
@@ -62,16 +63,70 @@
 public final class TypedAstIntegrationTest extends IntegrationTestCase {
 
   private ArrayList<Path> shards;
-  private ArrayList<SourceFile> externFiles;
-  private ArrayList<SourceFile> sourceFiles;
+  private ArrayList<SourceFile> stubExternFiles;
+  private ArrayList<SourceFile> stubSourceFiles;
 
   @Override
   @Before
   public void setUp() {
     super.setUp();
     this.shards = new ArrayList<>();
-    this.externFiles = new ArrayList<>();
-    this.sourceFiles = new ArrayList<>();
+    this.stubExternFiles = new ArrayList<>();
+    this.stubSourceFiles = new ArrayList<>();
+  }
+
+  @Test
+  public void compilerGeneratesErrorReportWithoutCrashing() throws IOException {
+    SourceFile lib1 =
+        code("\n\n class Lib1 { m() { return 'lib1'; } n() { return 'delete me'; } }");
+    SourceFile lib2 =
+        code("\n\n class Lib2 { m() { return 'delete me'; } n() { return 'lib2'; } }");
+    precompileLibrary(lib1);
+    precompileLibrary(lib2);
+    precompileLibrary(
+        extern(new TestExternsBuilder().addAlert().build()),
+        typeSummary(lib1),
+        typeSummary(lib2),
+        code("\n\n alert(new Lib1().m()); \n\n alert(new Lib2().n());"));
+    // assigning an instance of Lib1 to a variable of type 'string' causes the disambiguator to
+    // 'invalidate' the type of Lib1 and any associated properties.
+    SourceFile invalidating =
+        code("/** @suppress {checkTypes} @type {string} */ \n\n\n const str = new Lib1();");
+    precompileLibrary(typeSummary(lib1), invalidating);
+
+    CompilerOptions options = new CompilerOptions();
+    CompilationLevel.ADVANCED_OPTIMIZATIONS.setOptionsForCompilationLevel(options);
+    options.setDependencyOptions(DependencyOptions.none());
+    options.setDisambiguateProperties(true);
+    options.setPropertiesThatMustDisambiguate(ImmutableSet.of("m"));
+
+    Compiler compiler = compileTypedAstShardsWithoutErrorChecks(options);
+
+    assertThat(compiler.getErrors())
+        .comparingElementsUsing(JSCompCorrespondences.DESCRIPTION_EQUALITY)
+        .containsExactly(
+            "Property 'm' was required to be disambiguated but was invalidated."
+            );
+
+    // This code path pipes through the {@link ErrorManager} which extends the
+    // {@link BasicErrorManager}. The {@link BasicErrorManager} uses a {@link
+    // LightweightMessageFormatter} to format the error messages seen by the compiler. When doing
+    // so, it tries to format the error message using the compiler which extends the {@link
+    // SourceExceptProvider} to attach the relevant snippet of the source files. It invokes
+    // {@link SourceExceptProvider}'s methods such as {@link getSourceLine()}, etc to get the source
+    // code. For stage 2 and stage 3 passes, the compiler (and these tests) does not receive the
+    // source files. So, the {@link SourceExceptProvider} backs off from reading the source files.
+    // TODO(b/379868495): The `JSC_DISAMBIGUATE2_PROPERTY_INVALIDATION` error in this test is not a
+    // good example to test the crashing behavior when it is reported by the compiler. It is not a
+    // good example because it is a `JSError` that is created in the disambiguator pass without
+    // source details (line number, column number, etc) -
+    // https://source.corp.google.com/piper///depot/google3/third_party/java_src/jscomp/java/com/google/javascript/jscomp/disambiguate/DisambiguateProperties.java;rcl=665086807;l=235. When such an error is formatted, the {@link
+    // LightweightMessageFormatter}
+    // anyway backs off from extracting the source snippet and formatting it -
+    // https://source.corp.google.com/piper///depot/google3/third_party/java_src/jscomp/java/com/google/javascript/jscomp/LightweightMessageFormatter.java;rcl=645071015;l=175.
+    // A better example would be an error that is reported in the stage 2 or stage 3 pass and
+    // includes the relevant source code details.
+    compiler.generateReport();
   }
 
   @Test
@@ -230,8 +285,10 @@ public void disambiguatesAndDeletesMethodsAcrossLibraries_ignoresInvalidationsIn
     // However, leave in the associated TypedAST in this.shards.
     // We want to verify that JSCompiler is able to disambiguate properties on Lib1 despite the
     // invalidation in the unused TypedAST shard.
-    Preconditions.checkState(this.sourceFiles.get(3) == invalidating, this.sourceFiles);
-    this.sourceFiles.remove(3);
+    Preconditions.checkState(
+        Objects.equals(this.stubSourceFiles.get(3).getName(), invalidating.getName()),
+        this.stubSourceFiles);
+    this.stubSourceFiles.remove(3);
 
     Compiler compiler = compileTypedAstShards(options);
 
@@ -298,9 +355,9 @@ public void exportAnnotationOnProperty_ignoredInUnusedTypedAstShard() throws IOE
     // However, leave in the associated TypedAST in this.shards.
     // We want to verify that JSCompiler does /not/ pay attention to the @export in
     // the unusedLib file, as it's not part of the compilation.
-    Preconditions.checkState(this.sourceFiles.size() == 2, this.sourceFiles);
+    Preconditions.checkState(this.stubSourceFiles.size() == 2, this.stubSourceFiles);
     Preconditions.checkState(this.shards.size() == 2, this.shards);
-    this.sourceFiles.remove(1);
+    this.stubSourceFiles.remove(1);
 
     Compiler compiler = compileTypedAstShards(options);
 
@@ -512,7 +569,7 @@ public void runsJ2clOptimizations() throws IOException {
                 "  InternalWidget.$clinit();",
                 "};",
                 "InternalWidget.$clinit();"));
-    sourceFiles.add(f);
+    stubSourceFiles.add(f);
     precompileLibrary(f);
 
     CompilerOptions options = new CompilerOptions();
@@ -576,7 +633,7 @@ public void testCrossChunkMethodMotion() throws IOException {
     // run compilation
     try (InputStream inputStream = toInputStream(this.shards)) {
       compiler.initChunksWithTypedAstFilesystem(
-          ImmutableList.copyOf(this.externFiles),
+          ImmutableList.copyOf(this.stubExternFiles),
           ImmutableList.of(chunk1, chunk2),
           options,
           inputStream);
@@ -842,8 +899,8 @@ private Compiler compileTypedAstShardsWithoutErrorChecks(CompilerOptions options
     compiler.initOptions(options);
     try (InputStream inputStream = toInputStream(this.shards)) {
       compiler.initWithTypedAstFilesystem(
-          ImmutableList.copyOf(this.externFiles),
-          ImmutableList.copyOf(this.sourceFiles),
+          ImmutableList.copyOf(this.stubExternFiles),
+          ImmutableList.copyOf(this.stubSourceFiles),
           options,
           inputStream);
     }
@@ -852,6 +909,8 @@ private Compiler compileTypedAstShardsWithoutErrorChecks(CompilerOptions options
       compiler.stage3Passes();
     }
 
+    compiler.generateReport();
+
     return compiler;
   }
 
@@ -864,15 +923,19 @@ private Compiler compileTypedAstShards(CompilerOptions options) throws IOExcepti
 
   private SourceFile code(String... code) {
     SourceFile sourceFile =
-        SourceFile.fromCode("input_" + (sourceFiles.size() + 1), lines(code), SourceKind.STRONG);
-    this.sourceFiles.add(sourceFile);
+        SourceFile.fromCode(
+            "input_" + (stubSourceFiles.size() + 1), lines(code), SourceKind.STRONG);
+    SourceFile stubFile = SourceFile.stubSourceFile(sourceFile.getName(), SourceKind.STRONG);
+    this.stubSourceFiles.add(stubFile);
     return sourceFile;
   }
 
   private SourceFile extern(String... code) {
     SourceFile sourceFile =
-        SourceFile.fromCode("extern_" + (externFiles.size() + 1), lines(code), SourceKind.EXTERN);
-    this.externFiles.add(sourceFile);
+        SourceFile.fromCode(
+            "extern_" + (stubExternFiles.size() + 1), lines(code), SourceKind.EXTERN);
+    SourceFile stubFile = SourceFile.stubSourceFile(sourceFile.getName(), SourceKind.STRONG);
+    this.stubExternFiles.add(stubFile);
     return sourceFile;
   }