Improve error handling

Author: wenli-cai

workflow-trace-viewer/src/jvmMain/kotlin/com/squareup/workflow1/traceviewer/ui/WorkflowTree.kt

@@ -20,6 +20,7 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.unit.dp
 import com.squareup.workflow1.traceviewer.model.Node
+import com.squareup.workflow1.traceviewer.util.ParseResult
 import com.squareup.workflow1.traceviewer.util.parseTrace
 import io.github.vinceglb.filekit.PlatformFile
 
@@ -33,17 +34,31 @@ public fun RenderDiagram(
   frameInd: Int,
   onFileParse: (List<Node>) -> Unit,
   onNodeSelect: (Node) -> Unit,
+  modifier: Modifier = Modifier
 ) {
   var frames by remember { mutableStateOf<List<Node>>(emptyList()) }
-  var isLoading by remember { mutableStateOf(true) }
+  var isLoading by remember(traceFile) { mutableStateOf(true) }
+  var error by remember(traceFile) { mutableStateOf<Throwable?>(null) }
 
   LaunchedEffect(traceFile) {
-    isLoading = true
-    frames = parseTrace(traceFile)
-    onFileParse(frames)
+    val parseResult = parseTrace(traceFile)
+
+    if (parseResult is ParseResult.Failure) {
+      error = parseResult.error
+      return@LaunchedEffect
+    }
+
+    val parsedFrames = (parseResult as ParseResult.Success).trace ?: emptyList()
+    frames = parsedFrames
+    onFileParse(parsedFrames)
     isLoading = false
   }
 
+  if (error != null) {
+    Text("Error parsing file: ${error?.message}")
+    return
+  }
+
   if (!isLoading) {
     DrawTree(frames[frameInd], onNodeSelect)
   }

workflow-trace-viewer/src/jvmMain/kotlin/com/squareup/workflow1/traceviewer/util/JsonParser.kt

@@ -1,35 +1,37 @@
 package com.squareup.workflow1.traceviewer.util
 
 import com.squareup.moshi.JsonAdapter
-import com.squareup.moshi.JsonDataException
 import com.squareup.moshi.Moshi
 import com.squareup.moshi.Types
 import com.squareup.moshi.kotlin.reflect.KotlinJsonAdapterFactory
 import com.squareup.workflow1.traceviewer.model.Node
 import io.github.vinceglb.filekit.PlatformFile
 import io.github.vinceglb.filekit.readString
-import java.io.IOException
 
 /**
- * Parses a given file's JSON String into [Node] with Moshi adapters. Moshi automatically throws JsonDataException
- * and IOException
- * @throws JsonDataException malformed JSON data or an error reading.
- * @throws IOException JSON is correct, but mismatch between class and JSON structure.
+ * Parses a given file's JSON String into [Node] with Moshi adapters.
+ *
+ * @return A [ParseResult] representing result of parsing, either an error related to the
+ * format of the JSON, or a success and a parsed trace.
  */
 public suspend fun parseTrace(
   file: PlatformFile,
-): List<Node> {
-  val jsonString = file.readString()
-
-  val moshi = Moshi.Builder()
-    .add(KotlinJsonAdapterFactory())
-    .build()
-
-  val workflowList = Types.newParameterizedType(List::class.java, Node::class.java)
-  val workflowAdapter: JsonAdapter<List<Node>> = moshi.adapter(workflowList)
-  val trace = workflowAdapter.fromJson(jsonString)
-  if (trace == null) {
-    throw JsonDataException("Could not parse JSON")
+): ParseResult {
+  return try {
+    val jsonString = file.readString()
+    val moshi = Moshi.Builder()
+      .add(KotlinJsonAdapterFactory())
+      .build()
+    val workflowList = Types.newParameterizedType(List::class.java, Node::class.java)
+    val workflowAdapter: JsonAdapter<List<Node>> = moshi.adapter(workflowList)
+    val trace = workflowAdapter.fromJson(jsonString)
+    ParseResult.Success(trace)
+  } catch (e: Exception) {
+    ParseResult.Failure(e)
   }
-  return trace
+}
+
+sealed interface ParseResult {
+  class Success(val trace: List<Node>?) : ParseResult
+  class Failure(val error: Throwable) : ParseResult
 }