Sourcemap: source mapping

src/error.ts

@@ -32,7 +32,7 @@ export const colorWarning = (message: string): string => {
 }
 
 export const prettySourceMessage = (message: string, span: Span, source: Source, notes: string[] = []): string => {
-    const start = indexToLocation(span.start, source)!
+    const start = indexToLocation(span.start, source.code)!
     const locationStr = `${source.filepath}:${locationToString(start)}`
     const locationMsg = `  at ${locationStr}`
     const notesStr = notes.length > 0 ? notes.map(n => `  note: ${n}`).join('\n') : ''

src/index.ts

@@ -15,7 +15,7 @@ import { Context, pathToVid } from './scope'
 import { buildInstanceRelations } from './scope/trait'
 import { checkModule, checkTopLevelDefinition, prepareModule } from './semantic'
 import { Source } from './source'
-import { foldEmitTree } from './sourcemap'
+import { createSourceMap, foldEmitTree } from './sourcemap'
 import { assert } from './util/todo'
 
 const dir = dirname(fileURLToPath(import.meta.url))
@@ -202,9 +202,25 @@ if (config.emit) {
             const mainFnName = mainFn?.kind === 'fn-def' ? mainFn.name.value : undefined
             const emitNode = emitModule(m, ctx, mainFnName)
             const { emit, map } = foldEmitTree(emitNode)
-            const js = [emit, native].filter(m => m.length > 0).join('\n\n')
+
+            const sourceMapLink = `//# sourceMappingURL=${moduleOutPath.name}.js.map`
+            const js = [emit, native, sourceMapLink].filter(m => m.length > 0).join('\n\n')
             const jsPath = join(moduleOutPath.dir, moduleOutPath.name) + '.js'
             writeFile(jsPath, js).then(() => console.info(`emit: js           ${jsPath} [${js.length}B]`))
+
+            const sourceMap = JSON.stringify(
+                createSourceMap(
+                    basename(jsPath),
+                    relative(moduleOutPath.dir, m.source.filepath),
+                    m.source.code,
+                    js,
+                    map
+                )
+            )
+            const sourceMapPath = join(moduleOutPath.dir, moduleOutPath.name) + '.js.map'
+            writeFile(sourceMapPath, sourceMap).then(() =>
+                console.info(`emit: source map   ${sourceMapPath} [${sourceMap.length}B]`)
+            )
         })
     } else {
         const m = pkg.modules[0]
@@ -215,7 +231,7 @@ if (config.emit) {
                 : undefined
         const mainFnName = mainFn?.kind === 'fn-def' ? mainFn.name.value : undefined
         const emitNode = emitModule(m, ctx, mainFnName)
-        const { emit, map } = foldEmitTree(emitNode)
+        const { emit } = foldEmitTree(emitNode)
         const jsPath = join(config.outPath, parse(config.pkgPath).name) + '.js'
         writeFile(jsPath, emit).then(() => console.info(`emit: js           ${jsPath} [${emit.length}B]`))
     }

src/location.ts

@@ -17,11 +17,11 @@ export interface Location {
     column: number
 }
 
-export const indexToLocation = (index: number, source: Source): Location | undefined => {
+export const indexToLocation = (index: number, code: string): Location | undefined => {
     let line = 0
     let column = 0
     for (let i = 0; i < index; i++) {
-        if (isNewline(source.code[i])) {
+        if (isNewline(code[i])) {
             line++
             column = 0
         } else {
@@ -32,8 +32,8 @@ export const indexToLocation = (index: number, source: Source): Location | undef
 }
 
 export const prettyLineAt = (span: Span, source: Source): string => {
-    const start = indexToLocation(span.start, source)
-    const end = indexToLocation(span.end, source)
+    const start = indexToLocation(span.start, source.code)
+    const end = indexToLocation(span.end, source.code)
     if (!start || !end) return '<outside of a file>'
     const lineNumSize = start.line.toString().length
     const padSize = Math.max(6, 3 + lineNumSize)

src/sourcemap/index.ts

@@ -1,6 +1,16 @@
 import { EmitNode } from '../codegen/js/node'
-import { Span } from '../location'
+import { Span, indexToLocation } from '../location'
 import { getSpan } from '../parser'
+import { encode } from './base64vlq'
+
+export interface SourceMap {
+    version: number
+    file: string
+    sourceRoot: string
+    sources: string[]
+    names: string[]
+    mappings: string
+}
 
 export const foldEmitTree = (node: EmitNode, index: number = 0): { emit: string; map: [Span, Span][] } => {
     const map: [Span, Span][] = []
@@ -25,5 +35,70 @@ export const foldEmitTree = (node: EmitNode, index: number = 0): { emit: string;
         const span = getSpan(node.parseNode)
         map.push([span, { start, end: index + 1 }])
     }
-    return { emit, map }
+    return { emit, map: map.toSorted(([, ad], [, bd]) => ad.start - bd.start) }
+}
+
+export const createSourceMap = (
+    outFilename: string,
+    srcPath: string,
+    src: string,
+    out: string,
+    map: [Span, Span][]
+): SourceMap => {
+    const lines = []
+    let line = []
+    let sLine: number | undefined
+    let sCol: number | undefined
+    let dLine: number | undefined
+    let dCol: number | undefined
+
+    for (const [sSpan, dSpan] of map) {
+        const ms = []
+        const sLoc = indexToLocation(sSpan.start, src)!
+        const dLoc = indexToLocation(dSpan.start, out)!
+
+        if (dLine !== undefined && dLine !== dLoc.line) {
+            lines.push(line)
+            line = []
+            dCol = undefined
+        }
+
+        if (dCol !== undefined) {
+            ms.push(dLoc.column - dCol)
+        } else {
+            ms.push(dLoc.column)
+        }
+
+        ms.push(0)
+
+        if (sLine !== undefined) {
+            ms.push(sLoc.line - sLine)
+        } else {
+            ms.push(sLoc.line)
+        }
+
+        if (sCol !== undefined) {
+            ms.push(sLoc.column - sCol)
+        } else {
+            ms.push(sLoc.column)
+        }
+
+        dLine = dLoc.line
+        dCol = dLoc.column
+        sLine = sLoc.line
+        sCol = sLoc.column
+
+        line.push(ms.map(encode).join(''))
+    }
+    if (line.length > 0) {
+        lines.push(line)
+    }
+    return {
+        version: 3,
+        file: outFilename,
+        sourceRoot: '',
+        sources: [srcPath],
+        names: [],
+        mappings: lines.join(';')
+    }
 }