Gate xz-utils hint to Linux only

The .tar.xz format is also used on macOS, where tar has built-in xz
support. Only show the xz-utils installation hint on Linux where the
tool may genuinely be missing. Adjust tests to verify platform-specific
behavior.

Author: cderv

src/tools/impl/tinytex.ts

@@ -192,8 +192,8 @@ async function install(
         async () => {
           const result = await unzip(pkgInfo.filePath);
           if (!result.success) {
-            const hint = pkgInfo.filePath.endsWith(".tar.xz")
-              ? "\nOn Linux, you may need to install xz-utils (e.g., apt install xz-utils)."
+            const hint = pkgInfo.filePath.endsWith(".tar.xz") && isLinux
+              ? "\nYou may need to install xz-utils (e.g., apt install xz-utils)."
               : "";
             throw new Error(
               `Failed to extract ${basename(pkgInfo.filePath)}.${hint}\n${result.stderr}`,

tests/unit/tools/tinytex.test.ts

@@ -13,6 +13,7 @@ import {
 import { getLatestRelease } from "../../../src/tools/github.ts";
 import { GitHubRelease, InstallContext, PackageInfo } from "../../../src/tools/types.ts";
 import { join } from "../../../src/deno_ral/path.ts";
+import { isLinux } from "../../../src/deno_ral/platform.ts";
 
 // ---- Pure logic tests for tinyTexPkgName ----
 
@@ -210,7 +211,7 @@ unitTest(
 );
 
 unitTest(
-  "install - extraction failure for .tar.xz includes xz-utils hint",
+  "install - extraction failure for .tar.xz includes xz-utils hint only on Linux",
   async () => {
     const workingDir = Deno.makeTempDirSync({ prefix: "quarto-tinytex-test" });
     try {
@@ -230,10 +231,17 @@ unitTest(
         await tinyTexInstallable.install(pkgInfo, context);
         throw new Error("Expected install to throw");
       } catch (e) {
-        assert(
-          e instanceof Error && e.message.includes("xz-utils"),
-          `Error message should mention xz-utils, got: ${e}`,
-        );
+        if (isLinux) {
+          assert(
+            e instanceof Error && e.message.includes("xz-utils"),
+            `On Linux, error should mention xz-utils, got: ${e}`,
+          );
+        } else {
+          assert(
+            e instanceof Error && !e.message.includes("xz-utils"),
+            `On non-Linux, error should not mention xz-utils, got: ${e}`,
+          );
+        }
       }
     } finally {
       Deno.removeSync(workingDir, { recursive: true });