Simplify error propagation and alerts

Author: jpenilla

web/src/lib/components/files/MultimodalFileInput.svelte

@@ -14,6 +14,8 @@
         fileTypeOverride: box.with(() => fileTypeOverride),
         defaultMode: box.with(() => defaultMode),
     });
+
+    // eslint-disable-next-line no-useless-assignment -- false positive for Svelte $bindable initialization
     state = instance;
 
     function handleDragOver(event: DragEvent) {

web/src/lib/components/files/index.svelte.ts

@@ -236,7 +236,9 @@ export class MultimodalFileInputState {
                 if (threw) {
                     throw e;
                 }
-                throw new Error(`Failed to fetch from URL: ${url}\nSome errors, such as those caused by CORS, will only print in the console.\nCause: ${e}`);
+                throw new Error(`Failed to fetch from URL: ${url}\nSome errors, such as those caused by CORS, will only print in the console.`, {
+                    cause: e,
+                });
             }
         });
     });

web/src/lib/diff-viewer.svelte.ts

@@ -19,7 +19,7 @@ import {
     parseLineRef,
     type UnresolvedLineSelection,
 } from "$lib/components/diff/concise-diff-view.svelte";
-import { countOccurrences, type LazyPromise, lazyPromise, animationFramePromise, yieldToBrowser } from "$lib/util";
+import { countOccurrences, type LazyPromise, lazyPromise, animationFramePromise, formatErrorWithCauses, yieldToBrowser } from "$lib/util";
 import { onDestroy, onMount, tick } from "svelte";
 import { VList } from "virtua/svelte";
 import { Context, Debounced, watch } from "runed";
@@ -740,7 +740,7 @@ export class MultiFileDiffViewerState {
         } catch (e) {
             this.clear(); // Clear any partially loaded state
             console.error("Failed to load patches:", e);
-            alert("Failed to load patches: " + e);
+            alert(formatErrorWithCauses(e));
             return false;
         } finally {
             // Let the last progress update render before closing the loading state

web/src/lib/open-diff-dialog.svelte.ts

@@ -3,7 +3,7 @@ import { DirectoryEntry, FileEntry, MultimodalFileInputState, type MultimodalFil
 import { SvelteSet } from "svelte/reactivity";
 import { type FileStatus } from "$lib/github.svelte";
 import { makeImageDetails, makeTextDetails, MultiFileDiffViewerState, type LoadPatchesOptions } from "$lib/diff-viewer.svelte";
-import { binaryFileDummyDetails, bytesEqual, isBinaryFile, isImageFile, parseMultiFilePatch, tryCompileRegex } from "$lib/util";
+import { binaryFileDummyDetails, bytesEqual, formatErrorWithCauses, isBinaryFile, isImageFile, parseMultiFilePatch, tryCompileRegex } from "$lib/util";
 import { createTwoFilesPatch } from "diff";
 
 export interface OpenDiffDialogProps {
@@ -77,13 +77,7 @@ export class OpenDiffDialogState {
             },
             async () => {
                 const isImageDiff = isImageFile(fileAMeta.name) && isImageFile(fileBMeta.name);
-                let blobA: Blob, blobB: Blob;
-                try {
-                    [blobA, blobB] = await Promise.all([fileA.resolve(), fileB.resolve()]);
-                } catch (e) {
-                    console.log("Failed to resolve files:", e);
-                    throw new Error("Failed to resolve files", { cause: e });
-                }
+                const [blobA, blobB] = await Promise.all([fileA.resolve(), fileB.resolve()]);
                 const [aBinary, bBinary] = await Promise.all([isBinaryFile(blobA), isBinaryFile(blobB)]);
                 if (aBinary || bBinary) {
                     if (!isImageDiff) {
@@ -262,7 +256,7 @@ export class OpenDiffDialogState {
             text = await blob.text();
         } catch (e) {
             console.error("Failed to resolve patch file:", e);
-            alert("Failed to resolve patch file: " + e);
+            alert(formatErrorWithCauses(e));
             return;
         }
         this.props.open.current = false;

web/src/lib/util.ts

@@ -374,6 +374,24 @@ export function capitalizeFirstLetter(val: string): string {
     return val.charAt(0).toUpperCase() + val.slice(1);
 }
 
+export function formatErrorWithCauses(error: unknown): string {
+    const parts: string[] = [];
+    const seen = new Set<unknown>();
+    let current: unknown = error;
+
+    while (current !== undefined && !seen.has(current)) {
+        seen.add(current);
+        parts.push(String(current));
+
+        if (!(current instanceof Error) || current.cause === undefined) {
+            break;
+        }
+        current = current.cause;
+    }
+
+    return parts.map((part, index) => (index === 0 ? part : `Cause: ${part}`)).join("\n");
+}
+
 export function countOccurrences(str: string, substr: string): number {
     let count = 0;
     let idx = 0;