Fix TinyTeX detection for empty directories

Quarto was incorrectly detecting TinyTeX when ~/.TinyTeX/ directory existed without binaries, reporting "Version: undefined" but marking the check as OK. This prevented fallback to valid TinyTeX installations in the system PATH.

The detection logic now validates both that the bin directory exists and contains the tlmgr binary before reporting TinyTeX as available.

Fixes #13730

Author: cderv

news/changelog-1.9.md

@@ -46,6 +46,7 @@ All changes included in 1.9:
 - ([#13661](https://github.com/quarto-dev/quarto-cli/issues/13661)): Fix LaTeX compilation errors when using `mermaid-format: svg` with PDF/LaTeX output. SVG diagrams are now written directly without HTML script tags. Note: `mermaid-format: png` is recommended for best compatibility. SVG format requires `rsvg-convert` (or Inkscape with `use-rsvg-convert: false`) in PATH for conversion to PDF, and may experience text clipping in diagrams with multi-line labels.
 - ([rstudio/tinytex-releases#49](https://github.com/rstudio/tinytex-releases/issues/49)): Fix detection of LuaTeX-ja missing file errors by matching both "File" and "file" in error messages.
 - ([#13667](https://github.com/quarto-dev/quarto-cli/issues/13667)): Fix LaTeX compilation error with Python error output containing caret characters.
+- ([#13730](https://github.com/quarto-dev/quarto-cli/issues/13730)): Fix TinyTeX detection when `~/.TinyTeX/` directory exists without binaries. Quarto now verifies that the bin directory and tlmgr binary exist before reporting TinyTeX as available, allowing proper fallback to system PATH installations.
 
 ## Projects
 

src/tools/impl/tinytex-info.ts

@@ -12,12 +12,15 @@ import { existsSync } from "../../deno_ral/fs.ts";
 import { os as platformOs } from "../../deno_ral/platform.ts";
 
 export function hasTinyTex(): boolean {
-  const installDir = tinyTexInstallDir();
-  if (installDir && existsSync(installDir)) {
-    return true;
-  } else {
-    return false;
+  const binDir = tinyTexBinDir();
+  if (!binDir) {
+    return false;  // No bin directory found
   }
+
+  // Check for tlmgr binary (critical package manager)
+  const tlmgrBinary = platformOs === "windows" ? "tlmgr.bat" : "tlmgr";
+  const tlmgrPath = join(binDir, tlmgrBinary);
+  return safeExistsSync(tlmgrPath);
 }
 
 export function tinyTexInstallDir(): string | undefined {
@@ -49,10 +52,16 @@ export function tinyTexBinDir(): string | undefined {
         if (safeExistsSync(winPath)) return winPath;
         return join(basePath, "bin\\windows\\");
       }
-      case "linux":
-        return join(basePath, `bin/${Deno.build.arch}-linux`);
-      case "darwin":
-        return join(basePath, "bin/universal-darwin");
+      case "linux": {
+        const linuxPath = join(basePath, `bin/${Deno.build.arch}-linux`);
+        if (safeExistsSync(linuxPath)) return linuxPath;
+        return undefined;
+      }
+      case "darwin": {
+        const darwinPath = join(basePath, "bin/universal-darwin");
+        if (safeExistsSync(darwinPath)) return darwinPath;
+        return undefined;
+      }
       default:
         return undefined;
     }