Optimize files size computing (#128)

-  Iterate through each mapping rather than the source and only look at the source to determine the number of columns contributing to each file's mapped bytes.
- Add new error types `InvalidMappingLine` (when source map references a line outside source lines) and `InvalidMappingColumn` (when source map reference a column beyond source column at the particular line)

src/app-error.ts

@@ -36,6 +36,19 @@ interface UnmappedBytesErrorContext {
   unmappedBytes: number;
 }
 
+interface InvalidMappingLineErrorContext {
+  code: 'InvalidMappingLine';
+  generatedLine: number;
+  maxLine: number;
+}
+
+interface InvalidMappingColumnErrorContext {
+  code: 'InvalidMappingColumn';
+  generatedLine: number;
+  generatedColumn: number;
+  maxColumn: number;
+}
+
 interface CannotOpenTempFileErrorContext {
   code: 'CannotOpenTempFile';
   error: Buffer;
@@ -46,6 +59,8 @@ export type ErrorContext =
   | CommonErrorContext
   | OneSourceSourceMapErrorContext
   | UnmappedBytesErrorContext
+  | InvalidMappingLineErrorContext
+  | InvalidMappingColumnErrorContext
   | CannotOpenTempFileErrorContext;
 
 export function getErrorMessage(context: ErrorContext): string {
@@ -71,6 +86,20 @@ See ${SOURCE_MAP_INFO_URL}`;
       return `Unable to map ${unmappedBytes}/${totalBytes} bytes (${bytesString}%)`;
     }
 
+    case 'InvalidMappingLine': {
+      const { generatedLine, maxLine } = context;
+
+      return `Your source map refers to generated line ${generatedLine}, but the source only contains ${maxLine} line(s).
+Check that you are using the correct source map.`;
+    }
+
+    case 'InvalidMappingColumn': {
+      const { generatedLine, generatedColumn, maxColumn } = context;
+
+      return `Your source map refers to generated column ${generatedColumn} on line ${generatedLine}, but the source only contains ${maxColumn} column(s) on that line.
+Check that you are using the correct source map.`;
+    }
+
     case 'CannotSaveFile':
       return 'Unable to save HTML to file';
 

src/explore.ts

@@ -21,7 +21,7 @@ export async function exploreBundle(
 
   const sourceMapData = await loadSourceMap(code, map);
 
-  const sizes = computeGeneratedFileSizes(sourceMapData);
+  const sizes = computeFileSizeMapOptimized(sourceMapData);
 
   const files = adjustSourcePaths(sizes.files, options);
 
@@ -86,65 +86,63 @@ async function loadSourceMap(codeFile: File, sourceMapFile?: File): Promise<Sour
 }
 
 /** Calculate the number of bytes contributed by each source file */
-function computeGeneratedFileSizes(sourceMapData: SourceMapData): FileSizes {
-  const spans = computeSpans(sourceMapData);
-
+function computeFileSizeMapOptimized(sourceMapData: SourceMapData): FileSizes {
+  const { consumer, codeFileContent } = sourceMapData;
+  const lines = codeFileContent.split('\n');
   const files: FileSizeMap = {};
-  let unmappedBytes = 0;
-  let totalBytes = 0;
-
-  for (let i = 0; i < spans.length; i++) {
-    const { numChars, source } = spans[i];
+  let mappedBytes = 0;
+
+  consumer.computeColumnSpans();
+
+  consumer.eachMapping(({ source, generatedLine, generatedColumn, lastGeneratedColumn }) => {
+    // Lines are 1-based
+    const line = lines[generatedLine - 1];
+    if (line === null) {
+      throw new AppError({
+        code: 'InvalidMappingLine',
+        generatedLine: generatedLine,
+        maxLine: lines.length,
+      });
+    }
 
-    totalBytes += numChars;
+    // Columns are 0-based
+    if (generatedColumn >= line.length) {
+      throw new AppError({
+        code: 'InvalidMappingColumn',
+        generatedLine: generatedLine,
+        generatedColumn: generatedColumn,
+        maxColumn: line.length,
+      });
+    }
 
-    if (source === null) {
-      unmappedBytes += numChars;
+    let mappingLength = 0;
+    if (lastGeneratedColumn !== null) {
+      if (lastGeneratedColumn >= line.length) {
+        throw new AppError({
+          code: 'InvalidMappingColumn',
+          generatedLine: generatedLine,
+          generatedColumn: lastGeneratedColumn,
+          maxColumn: line.length,
+        });
+      }
+      mappingLength = lastGeneratedColumn - generatedColumn + 1;
     } else {
-      files[source] = (files[source] || 0) + numChars;
+      mappingLength = line.length - generatedColumn;
     }
-  }
+    files[source] = (files[source] || 0) + mappingLength;
+    mappedBytes += mappingLength;
+  });
+
+  // Don't count newlines as original version didn't count newlines
+  const totalBytes = codeFileContent.length - lines.length + 1;
 
   return {
     files,
-    unmappedBytes,
+    unmappedBytes: totalBytes - mappedBytes,
     totalBytes,
   };
 }
 
-interface Span {
-  source: string | null;
-  numChars: number;
-}
-
-function computeSpans(sourceMapData: SourceMapData): Span[] {
-  const { consumer, codeFileContent } = sourceMapData;
-
-  const lines = codeFileContent.split('\n');
-  const spans: Span[] = [];
-  let numChars = 0;
-
-  let lastSource: string | null | undefined = undefined; // not a string, not null
-
-  for (let line = 1; line <= lines.length; line++) {
-    const lineText = lines[line - 1];
-    const numCols = lineText.length;
-
-    for (let column = 0; column < numCols; column++, numChars++) {
-      const { source } = consumer.originalPositionFor({ line, column });
-
-      if (source !== lastSource) {
-        lastSource = source;
-        spans.push({ source, numChars: 1 });
-      } else {
-        spans[spans.length - 1].numChars += 1;
-      }
-    }
-  }
-
-  return spans;
-}
-
 export function adjustSourcePaths(fileSizeMap: FileSizeMap, options: ExploreOptions): FileSizeMap {
   if (!options.noRoot) {
     const prefix = getCommonPathPrefix(Object.keys(fileSizeMap));

src/index.ts

@@ -20,6 +20,8 @@ export type ErrorCode =
   | 'NoSourceMap'
   | 'OneSourceSourceMap'
   | 'UnmappedBytes'
+  | 'InvalidMappingLine'
+  | 'InvalidMappingColumn'
   | 'CannotSaveFile'
   | 'CannotCreateTempFile'
   | 'CannotOpenTempFile';
@@ -71,3 +73,10 @@ export interface ExploreErrorResult {
 }
 
 export type BundlesAndFileTokens = (Bundle | string)[] | Bundle | string;
+
+// TODO: Remove when https://github.com/mozilla/source-map/pull/374 is merged
+declare module 'source-map' {
+  export interface MappingItem {
+    lastGeneratedColumn: number | null;
+  }
+}

tests/__snapshots__/app-error.test.ts.snap

@@ -12,6 +12,16 @@ exports['app-error getErrorMessage should create message for \'CannotSaveFile\'
 Unable to save HTML to file
 `
 
+exports['app-error getErrorMessage should create message for \'InvalidMappingColumn\' 1'] = `
+Your source map refers to generated column 81 on line 60, but the source only contains 80 column(s) on that line.
+Check that you are using the correct source map.
+`
+
+exports['app-error getErrorMessage should create message for \'InvalidMappingLine\' 1'] = `
+Your source map refers to generated line 60, but the source only contains 57 line(s).
+Check that you are using the correct source map.
+`
+
 exports['app-error getErrorMessage should create message for \'NoBundles\' 1'] = `
 No file(s) provided
 `

tests/app-error.test.ts

@@ -9,6 +9,13 @@ describe('app-error', function() {
       { code: 'NoSourceMap' },
       { code: 'OneSourceSourceMap', filename: 'foo.min.js' },
       { code: 'UnmappedBytes', totalBytes: 100, unmappedBytes: 70 },
+      { code: 'InvalidMappingLine', generatedLine: 60, maxLine: 57 },
+      {
+        code: 'InvalidMappingColumn',
+        generatedLine: 60,
+        generatedColumn: 81,
+        maxColumn: 80,
+      },
       { code: 'CannotSaveFile' },
       { code: 'CannotCreateTempFile' },
       {