fix: make fileTrie last-write-wins; warn on slug collisions

quartz/build.ts

@@ -10,6 +10,7 @@ import { filterContent } from "./processors/filter"
 import { emitContent } from "./processors/emit"
 import cfg from "../quartz"
 import { FilePath, FullSlug, joinSegments, slugifyFilePath } from "./util/path"
+import { detectSlugCollisions, formatCollisionWarning } from "./util/slugCollisions"
 import chokidar from "chokidar"
 import { ProcessedContent } from "./plugins/vfile"
 import { Argv, BuildCtx } from "./util/ctx"
@@ -22,6 +23,12 @@ import { randomIdNonSecure } from "./util/random"
 import { ChangeEvent, QuartzPageTypePluginInstance } from "./plugins/types"
 import { minimatch } from "minimatch"
 
+function reportSlugCollisions(content: ProcessedContent[]): void {
+  const collisions = detectSlugCollisions(content)
+  if (collisions.length === 0) return
+  console.warn(styleText("yellow", formatCollisionWarning(collisions)))
+}
+
 function getPageTypeExtensions(ctx: BuildCtx): Set<string> {
   const extensions = new Set<string>()
   const pageTypes = (ctx.cfg.plugins.pageTypes ?? []) as unknown as QuartzPageTypePluginInstance[]
@@ -123,6 +130,7 @@ async function buildQuartz(argv: Argv, mut: Mutex, clientRefresh: () => void) {
   }
 
   const parsedFiles = await parseMarkdown(ctx, filePaths)
+  reportSlugCollisions(parsedFiles)
   const filteredContent = filterContent(ctx, parsedFiles)
 
   await emitContent(ctx, filteredContent)
@@ -303,12 +311,11 @@ async function rebuild(changes: ChangeEvent[], clientRefresh: () => void, buildD
     const aliases = addVirtualPageSlugAliases(ctx.allSlugs, ptExtensions)
     ctx.allSlugs.push(...aliases)
   }
-  let processedFiles = filterContent(
+  const markdownContent = Array.from(contentMap.values())
-    ctx,
-    Array.from(contentMap.values())
     .filter((file) => file.type === "markdown")
-      .map((file) => file.content),
+    .map((file) => file.content)
-  )
+  reportSlugCollisions(markdownContent)
+  let processedFiles = filterContent(ctx, markdownContent)
 
   let emittedFiles = 0
 

quartz/util/fileTrie.test.ts

@@ -107,6 +107,64 @@ describe("FileTrie", () => {
       assert.strictEqual(trie.children[1].children[0].children[0].data, data2)
       assert.strictEqual(trie.children[1].children[0].children[0].children.length, 0)
     })
+
+    test("last-insert-wins on folder-note collision (matches emitter semantics)", () => {
+      const first = {
+        title: "First Folder Note",
+        slug: "foo/index",
+        filePath: "foo/foo.md",
+      }
+      const second = {
+        title: "Second Folder Note",
+        slug: "foo/index",
+        filePath: "foo/index.md",
+      }
+
+      trie.add(first)
+      trie.add(second)
+
+      assert.strictEqual(trie.children.length, 1)
+      assert.strictEqual(trie.children[0].slug, "foo/index")
+      assert.strictEqual(trie.children[0].data, second)
+    })
+
+    test("last-insert-wins on root-level index collision", () => {
+      const first = { title: "First", slug: "index", filePath: "a.md" }
+      const second = { title: "Second", slug: "index", filePath: "b.md" }
+
+      trie.add(first)
+      trie.add(second)
+
+      assert.strictEqual(trie.data, second)
+    })
+
+    test("collision does not affect sibling files in the same folder", () => {
+      const folderNoteA = {
+        title: "Folder Note A",
+        slug: "foo/index",
+        filePath: "foo/foo.md",
+      }
+      const folderNoteB = {
+        title: "Folder Note B",
+        slug: "foo/index",
+        filePath: "foo/index.md",
+      }
+      const sibling = {
+        title: "Sibling",
+        slug: "foo/alice",
+        filePath: "foo/alice.md",
+      }
+
+      trie.add(folderNoteA)
+      trie.add(sibling)
+      trie.add(folderNoteB)
+
+      assert.strictEqual(trie.children.length, 1)
+      assert.strictEqual(trie.children[0].slug, "foo/index")
+      assert.strictEqual(trie.children[0].data, folderNoteB)
+      assert.strictEqual(trie.children[0].children.length, 1)
+      assert.strictEqual(trie.children[0].children[0].data, sibling)
+    })
   })
 
   describe("filter", () => {

quartz/util/fileTrie.ts

@@ -69,7 +69,12 @@ export class FileTrieNode<T extends FileTrieData = ContentDetails> {
     if (path.length === 1) {
       // base case, we are at the end of the path
       if (segment === "index") {
-        this.data ??= file
+        // Last-insert-wins on collision. Matches the emitter's last-write-wins
+        // semantics at plugins/emitters/helpers.ts so the trie's data and the
+        // file on disk agree on which source file "owns" a colliding slug.
+        // Collision detection happens upstream in build.ts; this assignment is
+        // the fallback for any duplicates that still reach the trie.
+        this.data = file
       } else {
         this.makeChild(path, file)
       }

quartz/util/slugCollisions.test.ts

@@ -0,0 +1,145 @@
+import test, { describe } from "node:test"
+import assert from "node:assert"
+import { detectSlugCollisions, formatCollisionWarning } from "./slugCollisions"
+import { ProcessedContent } from "../plugins/vfile"
+import { FilePath, FullSlug } from "./path"
+
+function makeContent(
+  entries: Array<{ slug: string; relativePath?: string; filePath?: string }>,
+): ProcessedContent[] {
+  return entries.map((e) => {
+    const vfile = {
+      data: {
+        slug: e.slug as FullSlug,
+        relativePath: (e.relativePath ?? `${e.slug}.md`) as FilePath,
+        filePath: (e.filePath ?? `/vault/${e.relativePath ?? `${e.slug}.md`}`) as FilePath,
+      },
+    }
+    return [{ type: "root", children: [] }, vfile] as unknown as ProcessedContent
+  })
+}
+
+describe("detectSlugCollisions", () => {
+  test("returns empty array when there are no collisions", () => {
+    const content = makeContent([{ slug: "alice" }, { slug: "bob" }, { slug: "characters/index" }])
+    assert.deepStrictEqual(detectSlugCollisions(content), [])
+  })
+
+  test("returns empty array for empty input", () => {
+    assert.deepStrictEqual(detectSlugCollisions([]), [])
+  })
+
+  test("detects a two-file collision with winner = last file", () => {
+    const content = makeContent([
+      { slug: "foo/index", relativePath: "foo/foo.md" },
+      { slug: "foo/index", relativePath: "foo/index.md" },
+    ])
+    const collisions = detectSlugCollisions(content)
+    assert.strictEqual(collisions.length, 1)
+    assert.strictEqual(collisions[0]!.slug, "foo/index")
+    assert.strictEqual(collisions[0]!.files.length, 2)
+    assert.strictEqual(collisions[0]!.winner.relativePath, "foo/index.md")
+    assert.strictEqual(collisions[0]!.files[0]!.relativePath, "foo/foo.md")
+    assert.strictEqual(collisions[0]!.files[1]!.relativePath, "foo/index.md")
+  })
+
+  test("detects a three-file collision with all files listed, winner = last", () => {
+    const content = makeContent([
+      { slug: "bar/index", relativePath: "bar/_index.md" },
+      { slug: "bar/index", relativePath: "bar/bar.md" },
+      { slug: "bar/index", relativePath: "bar/index.md" },
+    ])
+    const collisions = detectSlugCollisions(content)
+    assert.strictEqual(collisions.length, 1)
+    assert.strictEqual(collisions[0]!.files.length, 3)
+    assert.strictEqual(collisions[0]!.winner.relativePath, "bar/index.md")
+  })
+
+  test("detects multiple separate collisions", () => {
+    const content = makeContent([
+      { slug: "a/index", relativePath: "a/a.md" },
+      { slug: "a/index", relativePath: "a/index.md" },
+      { slug: "b/index", relativePath: "b/b.md" },
+      { slug: "b/index", relativePath: "b/index.md" },
+      { slug: "unique" },
+    ])
+    const collisions = detectSlugCollisions(content)
+    assert.strictEqual(collisions.length, 2)
+    const slugs = collisions.map((c) => c.slug).sort()
+    assert.deepStrictEqual(slugs, ["a/index", "b/index"])
+  })
+
+  test("ignores entries without a slug", () => {
+    const content: ProcessedContent[] = [
+      ...makeContent([{ slug: "alice" }]),
+      [
+        { type: "root", children: [] },
+        { data: { slug: undefined, relativePath: "broken.md" } },
+      ] as unknown as ProcessedContent,
+    ]
+    assert.deepStrictEqual(detectSlugCollisions(content), [])
+  })
+
+  test("winner annotation matches fileTrie last-insert-wins semantics", () => {
+    // Glob order is alphabetical: foo/foo.md sorts before foo/index.md.
+    // Both the fileTrie and this detector must agree that the second file wins.
+    const content = makeContent([
+      { slug: "foo/index", relativePath: "foo/foo.md" },
+      { slug: "foo/index", relativePath: "foo/index.md" },
+    ])
+    const collisions = detectSlugCollisions(content)
+    assert.strictEqual(collisions[0]!.winner.relativePath, "foo/index.md")
+  })
+})
+
+describe("formatCollisionWarning", () => {
+  test("returns empty string for empty input", () => {
+    assert.strictEqual(formatCollisionWarning([]), "")
+  })
+
+  test("formats single collision with winner and shadowed markers", () => {
+    const content = makeContent([
+      { slug: "foo/index", relativePath: "foo/foo.md" },
+      { slug: "foo/index", relativePath: "foo/index.md" },
+    ])
+    const collisions = detectSlugCollisions(content)
+    const output = formatCollisionWarning(collisions)
+    assert.match(output, /1 slug collision detected/)
+    assert.match(output, /foo\/index/)
+    assert.match(output, /foo\/foo\.md .*\(shadowed\)/)
+    assert.match(output, /foo\/index\.md .*\(used for this URL\)/)
+  })
+
+  test("formats multiple collisions with count in header", () => {
+    const content = makeContent([
+      { slug: "a/index", relativePath: "a/a.md" },
+      { slug: "a/index", relativePath: "a/index.md" },
+      { slug: "b/index", relativePath: "b/b.md" },
+      { slug: "b/index", relativePath: "b/index.md" },
+    ])
+    const collisions = detectSlugCollisions(content)
+    const output = formatCollisionWarning(collisions)
+    assert.match(output, /2 slug collisions detected/)
+    assert.match(output, /a\/index/)
+    assert.match(output, /b\/index/)
+  })
+
+  test("output mentions Folder Notes convention as a common cause", () => {
+    const content = makeContent([
+      { slug: "foo/index", relativePath: "foo/foo.md" },
+      { slug: "foo/index", relativePath: "foo/index.md" },
+    ])
+    const output = formatCollisionWarning(detectSlugCollisions(content))
+    assert.match(output, /Folder Notes/)
+  })
+
+  test("falls back to filePath when relativePath is missing", () => {
+    const content = makeContent([
+      { slug: "x/index", relativePath: "", filePath: "/vault/x/x.md" },
+      { slug: "x/index", relativePath: "", filePath: "/vault/x/index.md" },
+    ])
+    const output = formatCollisionWarning(detectSlugCollisions(content))
+    assert.match(output, /\/vault\/x\/x\.md/)
+    assert.match(output, /\/vault\/x\/index\.md/)
+  })
+})

quartz/util/slugCollisions.ts

@@ -0,0 +1,84 @@
+import { ProcessedContent } from "../plugins/vfile"
+import { FullSlug } from "./path"
+
+/**
+ * A slug collision: two or more source files that produce the same FullSlug
+ * after slugifyFilePath. The `winner` is the file whose HTML output and trie
+ * data represent this slug in the final build (see fileTrie.ts and the
+ * emitter's last-write-wins semantics in plugins/emitters/helpers.ts).
+ *
+ * `files` is in the order the files appear in the parsed content array
+ * (glob order), which is deterministic. `winner` is always the last entry.
+ */
+export interface SlugCollision {
+  slug: FullSlug
+  files: Array<{ relativePath: string; filePath: string }>
+  winner: { relativePath: string; filePath: string }
+}
+
+export function detectSlugCollisions(content: ProcessedContent[]): SlugCollision[] {
+  const bySlug = new Map<FullSlug, Array<{ relativePath: string; filePath: string }>>()
+
+  for (const [, file] of content) {
+    const slug = file.data.slug
+    if (!slug) continue
+    const entry = {
+      relativePath: (file.data.relativePath ?? "") as string,
+      filePath: (file.data.filePath ?? "") as string,
+    }
+    const existing = bySlug.get(slug)
+    if (existing) {
+      existing.push(entry)
+    } else {
+      bySlug.set(slug, [entry])
+    }
+  }
+
+  const collisions: SlugCollision[] = []
+  for (const [slug, files] of bySlug) {
+    if (files.length < 2) continue
+    collisions.push({
+      slug,
+      files,
+      winner: files[files.length - 1]!,
+    })
+  }
+
+  return collisions
+}
+
+/**
+ * Format a list of collisions as a single human-readable warning block.
+ * Returns an empty string when there are no collisions so callers can
+ * unconditionally log the result.
+ */
+export function formatCollisionWarning(collisions: SlugCollision[]): string {
+  if (collisions.length === 0) return ""
+
+  const lines: string[] = []
+  const header =
+    collisions.length === 1
+      ? `Warning: 1 slug collision detected.`
+      : `Warning: ${collisions.length} slug collisions detected.`
+  lines.push(header)
+  lines.push(
+    `Multiple source files produced the same URL slug. The last-processed file wins; the others are shadowed and their content will not appear in the output.`,
+  )
+  lines.push("")
+
+  for (const collision of collisions) {
+    lines.push(`  slug \`${collision.slug}\``)
+    for (const file of collision.files) {
+      const marker = file === collision.winner ? "(used for this URL)" : "(shadowed)"
+      const path = file.relativePath || file.filePath || "(unknown source)"
+      lines.push(`    - ${path} ${marker}`)
+    }
+    lines.push("")
+  }
+
+  lines.push(
+    `To resolve, rename or delete all but one file per collided slug. This may include files using the Obsidian "Folder Notes" convention (\`folder/folder.md\`) that collide with an existing \`folder/index.md\`.`,
+  )
+
+  return lines.join("\n")
+}