Diffs: fall back on invalid language hints (#57902)

Merged via squash.

Prepared head SHA: 567ca3a56f
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Co-authored-by: gumadeiras <5599352+gumadeiras@users.noreply.github.com>
Reviewed-by: @gumadeiras

extensions/diffs/src/language-hints.ts

@@ -0,0 +1,39 @@
+import { resolveLanguage } from "@pierre/diffs";
+import type { SupportedLanguages } from "@pierre/diffs";
+
+const PASSTHROUGH_LANGUAGE_HINTS = new Set<SupportedLanguages>(["ansi", "text"]);
+
+export async function normalizeSupportedLanguageHint(
+  value?: string,
+): Promise<SupportedLanguages | undefined> {
+  const normalized = value?.trim();
+  if (!normalized) {
+    return undefined;
+  }
+  if (PASSTHROUGH_LANGUAGE_HINTS.has(normalized as SupportedLanguages)) {
+    return normalized as SupportedLanguages;
+  }
+  try {
+    await resolveLanguage(normalized as Exclude<SupportedLanguages, "text" | "ansi">);
+    return normalized as SupportedLanguages;
+  } catch {
+    return undefined;
+  }
+}
+
+export async function filterSupportedLanguageHints(
+  values: Iterable<string>,
+): Promise<SupportedLanguages[]> {
+  const supported = new Set<SupportedLanguages>();
+  for (const value of values) {
+    const normalized = await normalizeSupportedLanguageHint(value);
+    if (!normalized) {
+      continue;
+    }
+    supported.add(normalized);
+  }
+  if (supported.size === 0) {
+    supported.add("text");
+  }
+  return [...supported];
+}