WIP synchronous mapping

This replaces asynchronous `source-map` with a synchronous mapping implementation using `sourcemap-codec`. According to the performance test there is no noticeable difference at file lenghts like these - `source-map` is better at really large files (thousands of lines), which is not the case for 99,9% of all Svelte files the user will edit with this. A further (according to tests not noticeable) performance improvment would be to return the decoded form of the source map from svelte2tsx (it used sourcemap-coded, too).

The mapping implementation could also serve as a reference implementation for synchronous source mapping for TS plugin (sveltejs#580)

packages/language-server/package.json

@@ -53,6 +53,7 @@
         "prettier": "2.2.1",
         "prettier-plugin-svelte": "~2.1.0",
         "source-map": "^0.7.3",
+        "sourcemap-codec": "^1.4.8",
         "svelte": "~3.32.1",
         "svelte-preprocess": "~4.6.1",
         "svelte2tsx": "*",

packages/language-server/src/plugins/typescript/DocumentMapper.ts

@@ -1,29 +1,113 @@
+import { decode, SourceMapMappings, SourceMapSegment } from 'sourcemap-codec';
 import { Position } from 'vscode-languageserver';
-import { SourceMapConsumer } from 'source-map';
-import { SourceMapDocumentMapper } from '../../lib/documents';
+import { DocumentMapper } from '../../lib/documents';
 
-export class ConsumerDocumentMapper extends SourceMapDocumentMapper {
-    constructor(consumer: SourceMapConsumer, sourceUri: string, private nrPrependesLines: number) {
-        super(consumer, sourceUri);
-    }
+export class ConsumerDocumentMapper implements DocumentMapper {
+    private decoded?: SourceMapMappings;
+
+    constructor(
+        private rawMap: string,
+        private sourceUri: string,
+        private nrPrependesLines: number
+    ) {}
 
     getOriginalPosition(generatedPosition: Position): Position {
-        return super.getOriginalPosition(
-            Position.create(
-                generatedPosition.line - this.nrPrependesLines,
-                generatedPosition.character
-            )
+        if (generatedPosition.line < 0) {
+            return Position.create(-1, -1);
+        }
+
+        if (!this.decoded) {
+            this.decoded = decode(this.rawMap);
+        }
+
+        const position = Position.create(
+            generatedPosition.line - this.nrPrependesLines,
+            generatedPosition.character
+        );
+
+        if (position.line >= this.decoded.length) {
+            return Position.create(-1, -1);
+        }
+
+        const lineMatch = this.decoded[position.line];
+        if (!lineMatch.length) {
+            return Position.create(-1, -1);
+        }
+
+        const character = position.character;
+        const characterMatch = lineMatch.find(
+            (col, idx) =>
+                idx + 1 === lineMatch.length ||
+                (col[0] <= character && lineMatch[idx + 1][0] > character)
         );
+        if (!isValidSegment(characterMatch)) {
+            return Position.create(-1, -1);
+        }
+
+        return Position.create(characterMatch[2], characterMatch[3]);
     }
 
     getGeneratedPosition(originalPosition: Position): Position {
-        const result = super.getGeneratedPosition(originalPosition);
-        result.line += this.nrPrependesLines;
-        return result;
+        if (!this.decoded) {
+            this.decoded = decode(this.rawMap);
+        }
+
+        const lineMatches: [number, [number, number, number, number]][] = [];
+        for (let line = 0; line < this.decoded.length; line++) {
+            for (let column = 0; column < this.decoded[line].length; column++) {
+                const entry = this.decoded[line][column];
+                if (isSegmentOnSameLine(entry, originalPosition.line)) {
+                    lineMatches.push([line, entry]);
+                    if (entry[3] === originalPosition.character) {
+                        return Position.create(line + this.nrPrependesLines, entry[0]);
+                    }
+                }
+            }
+        }
+
+        if (!lineMatches.length) {
+            return Position.create(-1, -1);
+        }
+
+        // Since the mappings are high resolution, we should never get to this point,
+        // but we'll deal with it regardless.
+        lineMatches.sort((m1, m2) => {
+            const lineDiff = m1[0] - m2[0];
+            if (lineDiff !== 0) {
+                return lineDiff;
+            }
+            return m1[1][3] - m2[1][3];
+        });
+        const match = lineMatches.find(
+            (match, idx) =>
+                idx + 1 === lineMatches.length ||
+                (match[1][3] <= originalPosition.character &&
+                    lineMatches[idx + 1][1][3] > originalPosition.character)
+        )!;
+        return Position.create(match[1][2] + this.nrPrependesLines, match[0]);
     }
 
     isInGenerated(): boolean {
         // always return true and map outliers case by case
         return true;
     }
+
+    getURL(): string {
+        return this.sourceUri;
+    }
+
+    destroy() {}
+}
+
+function isSegmentOnSameLine(
+    segment: SourceMapSegment,
+    line: number
+): segment is [number, number, number, number] {
+    return segment[2] === line;
+}
+
+function isValidSegment(
+    segment: SourceMapSegment | undefined
+): segment is [number, number, number, number] {
+    return !!segment && segment.length > 1;
 }

packages/language-server/src/plugins/typescript/DocumentSnapshot.ts

@@ -266,11 +266,7 @@ export class SvelteDocumentSnapshot implements DocumentSnapshot {
         if (!this.tsxMap) {
             return new FragmentMapper(this.parent.getText(), scriptInfo, uri);
         }
-        return new ConsumerDocumentMapper(
-            await new SourceMapConsumer(this.tsxMap),
-            uri,
-            this.nrPrependedLines
-        );
+        return new ConsumerDocumentMapper(this.tsxMap.mappings, uri, this.nrPrependedLines);
     }
 }
 

yarn.lock

@@ -2339,7 +2339,7 @@ source-map@^0.6.0, source-map@^0.6.1:
   resolved "https://registry.yarnpkg.com/source-map/-/source-map-0.6.1.tgz#74722af32e9614e9c287a8d0bbde48b5e2f1a263"
   integrity sha512-UjgapumWlbMhkBgzT7Ykc5YXUT46F0iKu8SGXq0bcwP5dz/h0Plj6enJqjz1Zbq2l5WaqYnrVbwWOWMyF3F47g==
 
-sourcemap-codec@^1.4.4:
+sourcemap-codec@^1.4.4, sourcemap-codec@^1.4.8:
   version "1.4.8"
   resolved "https://registry.yarnpkg.com/sourcemap-codec/-/sourcemap-codec-1.4.8.tgz#ea804bd94857402e6992d05a38ef1ae35a9ab4c4"
   integrity sha512-9NykojV5Uih4lgo5So5dtw+f0JgJX30KCNI8gwhz2J9A15wD0Ml6tjHKwf6fTSa6fAdVBdZeNOs9eJ71qCk8vA==