Fix Travis CI issue with GWT composed sourcemaps

GWT does not support SourceMapResolver::getRelativePath

Author: lauraharker

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

@@ -295,7 +295,7 @@ public SourceFile loadSource(String filename) {
   private static class ResolvedSourceMap {
     public String originalPath;
     public String sourceMapPath;
-    public SourceFile sourceFile;
+    public String relativePath;
   }
 
   /**
@@ -2891,15 +2891,15 @@ public OriginalMapping getSourceMapping(String sourceName, int lineNumber, int c
     // First check to see if the original file was loaded from an input source map.
     String sourceMapOriginalPath = sourceMap.getOriginalPath();
     String resultOriginalPath = result.getOriginalFile();
-    SourceFile source = null;
+    final String relativePath;
 
     // Resolving the paths to a source file is expensive, so check the cache first.
     if (sourceMapOriginalPath.equals(resolvedSourceMap.originalPath)
         && resultOriginalPath.equals(resolvedSourceMap.sourceMapPath)) {
-      source = resolvedSourceMap.sourceFile;
+      relativePath = resolvedSourceMap.relativePath;
     } else {
-      String relativePath = resolveSibling(sourceMapOriginalPath, resultOriginalPath);
-      source = getSourceFileByName(relativePath);
+      relativePath = resolveSibling(sourceMapOriginalPath, resultOriginalPath);
+      SourceFile source = getSourceFileByName(relativePath);
       if (source == null && !isNullOrEmpty(resultOriginalPath)) {
         source =
             SourceMapResolver.getRelativePath(
@@ -2912,11 +2912,11 @@ public OriginalMapping getSourceMapping(String sourceName, int lineNumber, int c
       // Cache this resolved source for the next caller.
       resolvedSourceMap.originalPath = sourceMapOriginalPath;
       resolvedSourceMap.sourceMapPath = resultOriginalPath;
-      resolvedSourceMap.sourceFile = source;
+      resolvedSourceMap.relativePath = relativePath;
     }
 
     return result.toBuilder()
-        .setOriginalFile(source.getOriginalPath())
+        .setOriginalFile(relativePath)
         .setColumnPosition(result.getColumnPosition() - 1)
         .build();
   }

test/com/google/javascript/jscomp/SourceMapTest.java

@@ -20,6 +20,7 @@
 
 import com.google.common.base.Joiner;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
 import com.google.debugging.sourcemap.SourceMapConsumer;
 import com.google.debugging.sourcemap.SourceMapConsumerV3;
 import com.google.debugging.sourcemap.SourceMapTestCase;
@@ -38,6 +39,7 @@ public final class SourceMapTest extends SourceMapTestCase {
   public SourceMapTest() {}
 
   private List<SourceMap.LocationMapping> mappings;
+  private ImmutableMap.Builder<String, SourceMapInput> inputMaps;
 
   @Test
   public void testPrefixReplacement1() throws IOException {
@@ -149,19 +151,49 @@ public void testLambdaReplacement() throws IOException {
                 "}\n"));
   }
 
+  // This is taken from SourceMapJsLangTest. That test can't run under J2CL because it
+  // uses a parameterized runner but we do want to test this basic behavior under J2CL.
+  @Test
+  public void testRepeatedCompilation() throws Exception {
+    // Run compiler twice feeding sourcemaps from the first run as input to the second run.
+    // This way we ensure that compiler works fine with its own sourcemaps and doesn't lose
+    // important information.
+    String fileContent = "function foo() {} alert(foo());";
+    String fileName = "foo.js";
+    RunResult firstCompilation = compile(fileContent, fileName);
+    String newFileName = fileName + ".compiled";
+    inputMaps.put(
+        newFileName,
+        new SourceMapInput(
+            SourceFile.fromCode("sourcemap", firstCompilation.sourceMapFileContent)));
+
+    RunResult secondCompilation = compile(firstCompilation.generatedSource, newFileName);
+    check(
+        fileName,
+        fileContent,
+        secondCompilation.generatedSource,
+        secondCompilation.sourceMapFileContent);
+  }
+
   @Override
   protected CompilerOptions getCompilerOptions() {
     CompilerOptions options = super.getCompilerOptions();
     if (mappings != null) {
       options.sourceMapLocationMappings = mappings;
     }
+
+    if (!this.inputMaps.build().isEmpty()) {
+      options.setApplyInputSourceMaps(true);
+      options.setInputSourceMaps(this.inputMaps.build());
+    }
     return options;
   }
 
   @Override
   @Before
   public void setUp() {
     super.setUp();
+    this.inputMaps = ImmutableMap.builder();
   }
 
   private void checkSourceMap2(