[JS] Factor out source map path rewriting

compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/dce/K2JSDce.kt

@@ -124,37 +124,29 @@ class K2JSDce : CLITool<K2JSDceArguments>() {
     }
 
     private fun mapSourcePaths(inputFile: File, targetFile: File): Boolean {
-        val json = try {
+        val jsonOut = StringWriter()
-            parseJson(inputFile)
-        } catch (e: JsonSyntaxException) {
-            return false
-        }
-
-        val sourcesArray = (json as? JsonObject)?.properties?.get("sources") as? JsonArray ?: return false
-        val sources = sourcesArray.elements.map {
-            (it as? JsonString)?.value ?: return false
-        }
-
         val pathCalculator = RelativePathCalculator(targetFile.parentFile)
-        val mappedSources = sources.map {
+        val sourceMapChanged = try {
-            val result = pathCalculator.calculateRelativePathTo(File(inputFile.parentFile, it))
+            SourceMap.mapSources(inputFile.readText(), jsonOut) {
-            if (result != null) {
+                val result = pathCalculator.calculateRelativePathTo(File(inputFile.parentFile, it))
-                if (File(targetFile.parentFile, result).exists()) {
+                if (result != null) {
-                    result
+                    if (File(targetFile.parentFile, result).exists()) {
+                        result
+                    } else {
+                        it
+                    }
                 } else {
                     it
                 }
-            } else {
-                it
             }
+        } catch (e: SourceMapSourceReplacementException) {
+            false
         }
 
-        if (mappedSources == sources) return false
+        if (!sourceMapChanged) return false
-
-        json.properties["sources"] = JsonArray(*mappedSources.map { JsonString(it) }.toTypedArray())
 
         targetFile.parentFile.mkdirs()
-        OutputStreamWriter(FileOutputStream(targetFile), "UTF-8").use { it.write(json.toString()) }
+        OutputStreamWriter(FileOutputStream(targetFile), "UTF-8").use { it.write(jsonOut.toString()) }
 
         return true
     }

js/js.parser/src/org/jetbrains/kotlin/js/parser/sourcemaps/SourceMap.kt

@@ -16,9 +16,7 @@
 
 package org.jetbrains.kotlin.js.parser.sourcemaps
 
-import java.io.File
+import java.io.*
-import java.io.PrintStream
-import java.io.Reader
 
 class SourceMap(val sourceContentResolver: (String) -> Reader?) {
     val groups = mutableListOf<SourceMapGroup>()
@@ -49,8 +47,48 @@ class SourceMap(val sourceContentResolver: (String) -> Reader?) {
             writer.println()
         }
     }
+
+    companion object {
+        @Throws(IOException::class, SourceMapSourceReplacementException::class)
+        fun replaceSources(sourceMapFile: File, mapping: (String) -> String): Boolean {
+            val content = sourceMapFile.readText()
+            return sourceMapFile.writer().buffered().use {
+                mapSources(content, it, mapping)
+            }
+        }
+
+        @Throws(IOException::class, SourceMapSourceReplacementException::class)
+        fun mapSources(content: String, output: Writer, mapping: (String) -> String): Boolean {
+            val json = try {
+                parseJson(content)
+            } catch (e: JsonSyntaxException) {
+                throw SourceMapSourceReplacementException(cause = e)
+            }
+            val jsonObject = json as? JsonObject ?: throw SourceMapSourceReplacementException("Top-level object expected")
+            val sources = jsonObject.properties["sources"]
+            if (sources != null) {
+                val sourcesArray =
+                    sources as? JsonArray ?: throw SourceMapSourceReplacementException("'sources' property is not of array type")
+                var changed = false
+                val fixedSources = sourcesArray.elements.mapTo(mutableListOf<JsonNode>()) {
+                    val sourcePath = it as? JsonString ?: throw SourceMapSourceReplacementException("'sources' array must contain strings")
+                    val replacedPath = mapping(sourcePath.value)
+                    if (!changed && replacedPath != sourcePath.value) {
+                        changed = true
+                    }
+                    JsonString(replacedPath)
+                }
+                if (!changed) return false
+                jsonObject.properties["sources"] = JsonArray(fixedSources)
+            }
+            jsonObject.write(output)
+            return true
+        }
+    }
 }
 
+class SourceMapSourceReplacementException(message: String? = null, cause: Throwable? = null) : Exception(message, cause)
+
 data class SourceMapSegment(
     val generatedColumnNumber: Int,
     val sourceFileName: String?,