Refactor originalPositionFor to remove polymorphism

ampproject · Apr 23, 2022 · cfa1c9b · cfa1c9b
1 parent 90a5b6b
commit cfa1c9b
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Showing 5 changed files with 153 additions and 194 deletions.
diff --git a/src/build-source-map-tree.ts b/src/build-source-map-tree.ts
@@ -1,8 +1,8 @@
 import { TraceMap } from '@jridgewell/trace-mapping';
 
-import OriginalSource from './original-source';
-import { SourceMapTree } from './source-map-tree';
+import { OriginalSource, MapSource } from './source-map-tree';
 
+import type { Sources } from './source-map-tree';
 import type { SourceMapInput, SourceMapLoader, LoaderContext } from './types';
 
 function asArray<T>(value: T | T[]): T[] {
@@ -24,7 +24,7 @@ function asArray<T>(value: T | T[]): T[] {
 export default function buildSourceMapTree(
   input: SourceMapInput | SourceMapInput[],
   loader: SourceMapLoader
-): SourceMapTree {
+): Sources {
   const maps = asArray(input).map((m) => new TraceMap(m, ''));
   const map = maps.pop()!;
 
@@ -39,7 +39,7 @@ export default function buildSourceMapTree(
 
   let tree = build(map, loader, '', 0);
   for (let i = maps.length - 1; i >= 0; i--) {
-    tree = new SourceMapTree(maps[i], [tree]);
+    tree = MapSource(maps[i], [tree]);
   }
   return tree;
 }
@@ -49,44 +49,42 @@ function build(
   loader: SourceMapLoader,
   importer: string,
   importerDepth: number
-): SourceMapTree {
+): Sources {
   const { resolvedSources, sourcesContent } = map;
 
   const depth = importerDepth + 1;
-  const children = resolvedSources.map(
-    (sourceFile: string | null, i: number): SourceMapTree | OriginalSource => {
-      // The loading context gives the loader more information about why this file is being loaded
-      // (eg, from which importer). It also allows the loader to override the location of the loaded
-      // sourcemap/original source, or to override the content in the sourcesContent field if it's
-      // an unmodified source file.
-      const ctx: LoaderContext = {
-        importer,
-        depth,
-        source: sourceFile || '',
-        content: undefined,
-      };
+  const children = resolvedSources.map((sourceFile: string | null, i: number): Sources => {
+    // The loading context gives the loader more information about why this file is being loaded
+    // (eg, from which importer). It also allows the loader to override the location of the loaded
+    // sourcemap/original source, or to override the content in the sourcesContent field if it's
+    // an unmodified source file.
+    const ctx: LoaderContext = {
+      importer,
+      depth,
+      source: sourceFile || '',
+      content: undefined,
+    };
 
-      // Use the provided loader callback to retrieve the file's sourcemap.
-      // TODO: We should eventually support async loading of sourcemap files.
-      const sourceMap = loader(ctx.source, ctx);
+    // Use the provided loader callback to retrieve the file's sourcemap.
+    // TODO: We should eventually support async loading of sourcemap files.
+    const sourceMap = loader(ctx.source, ctx);
 
-      const { source, content } = ctx;
+    const { source, content } = ctx;
 
-      // If there is no sourcemap, then it is an unmodified source file.
-      if (!sourceMap) {
-        // The contents of this unmodified source file can be overridden via the loader context,
-        // allowing it to be explicitly null or a string. If it remains undefined, we fall back to
-        // the importing sourcemap's `sourcesContent` field.
-        const sourceContent =
-          content !== undefined ? content : sourcesContent ? sourcesContent[i] : null;
-        return new OriginalSource(source, sourceContent);
-      }
-
-      // Else, it's a real sourcemap, and we need to recurse into it to load its
-      // source files.
-      return build(new TraceMap(sourceMap, source), loader, source, depth);
+    // If there is no sourcemap, then it is an unmodified source file.
+    if (!sourceMap) {
+      // The contents of this unmodified source file can be overridden via the loader context,
+      // allowing it to be explicitly null or a string. If it remains undefined, we fall back to
+      // the importing sourcemap's `sourcesContent` field.
+      const sourceContent =
+        content !== undefined ? content : sourcesContent ? sourcesContent[i] : null;
+      return OriginalSource(source, sourceContent);
     }
-  );
 
-  return new SourceMapTree(map, children);
+    // Else, it's a real sourcemap, and we need to recurse into it to load its
+    // source files.
+    return build(new TraceMap(sourceMap, source), loader, source, depth);
+  });
+
+  return MapSource(map, children);
 }
diff --git a/src/original-source.ts b/src/original-source.ts
diff --git a/src/source-map-tree.ts b/src/source-map-tree.ts
@@ -2,20 +2,65 @@ import { FastStringArray, put } from './fast-string-array';
 import { presortedDecodedMap, traceSegment, decodedMappings } from '@jridgewell/trace-mapping';
 
 import type { TraceMap } from '@jridgewell/trace-mapping';
-import type OriginalSource from './original-source';
 import type { SourceMapSegment, SourceMapSegmentObject } from './types';
 
-type Sources = OriginalSource | SourceMapTree;
-
 const INVALID_MAPPING = undefined;
 const SOURCELESS_MAPPING = null;
+const EMPTY_SOURCES: Sources[] = [];
+
 type MappingSource = SourceMapSegmentObject | typeof INVALID_MAPPING | typeof SOURCELESS_MAPPING;
 
+type OriginalSource = {
+  map: TraceMap;
+  sources: Sources[];
+  source: string;
+  content: string | null;
+};
+
+type MapSource = {
+  map: TraceMap;
+  sources: Sources[];
+  source: string;
+  content: string | null;
+};
+
+export type Sources = OriginalSource | MapSource;
+
+function Source<M extends TraceMap | null>(
+  map: TraceMap | null,
+  sources: Sources[],
+  source: string,
+  content: string | null
+): M extends null ? OriginalSource : MapSource {
+  return {
+    map,
+    sources,
+    source,
+    content,
+  } as any;
+}
+
+/**
+ * MapSource represents a single sourcemap, with the ability to trace mappings into its child nodes
+ * (which may themselves be SourceMapTrees).
+ */
+export function MapSource(map: TraceMap, sources: Sources[]): MapSource {
+  return Source(map, sources, '', null);
+}
+
+/**
+ * A "leaf" node in the sourcemap tree, representing an original, unmodified source file. Recursive
+ * segment tracing ends at the `OriginalSource`.
+ */
+export function OriginalSource(source: string, content: string | null): OriginalSource {
+  return Source(null, EMPTY_SOURCES, source, content);
+}
+
 /**
  * traceMappings is only called on the root level SourceMapTree, and begins the process of
  * resolving each mapping in terms of the original source files.
  */
-export function traceMappings(tree: SourceMapTree): TraceMap {
+export function traceMappings(tree: Sources): TraceMap {
   const mappings: SourceMapSegment[][] = [];
   const names = FastStringArray();
   const sources = FastStringArray();
@@ -41,7 +86,8 @@ export function traceMappings(tree: SourceMapTree): TraceMap {
       // to gather from it.
       if (segment.length !== 1) {
         const source = rootSources[segment[1]];
-        traced = source.originalPositionFor(
+        traced = originalPositionFor(
+          source,
           segment[2],
           segment[3],
           segment.length === 5 ? rootNames[segment[4]] : ''
@@ -117,36 +163,31 @@ export function traceMappings(tree: SourceMapTree): TraceMap {
 }
 
 /**
- * SourceMapTree represents a single sourcemap, with the ability to trace
- * mappings into its child nodes (which may themselves be SourceMapTrees).
+ * originalPositionFor is only called on children SourceMapTrees. It recurses down into its own
+ * child SourceMapTrees, until we find the original source map.
  */
-export class SourceMapTree {
-  declare map: TraceMap;
-  declare sources: Sources[];
-
-  constructor(map: TraceMap, sources: Sources[]) {
-    this.map = map;
-    this.sources = sources;
+export function originalPositionFor(
+  source: Sources,
+  line: number,
+  column: number,
+  name: string
+): MappingSource {
+  if (!source.map) {
+    return { column, line, name, source: source.source, content: source.content };
   }
 
-  /**
-   * originalPositionFor is only called on children SourceMapTrees. It recurses down
-   * into its own child SourceMapTrees, until we find the original source map.
-   */
-  originalPositionFor(line: number, column: number, name: string): MappingSource {
-    const segment = traceSegment(this.map, line, column);
-
-    // If we couldn't find a segment, then this doesn't exist in the sourcemap.
-    if (segment == null) return INVALID_MAPPING;
-    // 1-length segments only move the current generated column, there's no source information
-    // to gather from it.
-    if (segment.length === 1) return SOURCELESS_MAPPING;
-
-    const source = this.sources[segment[1]];
-    return source.originalPositionFor(
-      segment[2],
-      segment[3],
-      segment.length === 5 ? this.map.names[segment[4]] : name
-    );
-  }
+  const segment = traceSegment(source.map, line, column);
+
+  // If we couldn't find a segment, then this doesn't exist in the sourcemap.
+  if (segment == null) return INVALID_MAPPING;
+  // 1-length segments only move the current generated column, there's no source information
+  // to gather from it.
+  if (segment.length === 1) return SOURCELESS_MAPPING;
+
+  return originalPositionFor(
+    source.sources[segment[1]],
+    segment[2],
+    segment[3],
+    segment.length === 5 ? source.map.names[segment[4]] : name
+  );
 }
diff --git a/test/unit/original-source.ts b/test/unit/original-source.ts