fix(ocr): find the snap's bundled tessdata under its tesseract prefix

app/tools/_ocr_paths.py

@@ -0,0 +1,138 @@
+"""Locate the Tesseract executable and its ``tessdata`` directory.
+
+Helpers for :mod:`app.tools.ocr`. This module has no Qt and no ``app.*``
+imports of its own, but importing it through the ``app.tools`` package
+loads Qt anyway (see ``app/tools/__init__.py``). ``app.tools.ocr``
+re-exports both names.
+
+The tests replace ``os.path.isdir``, ``glob.glob``, ``shutil.which`` and
+``sys.platform`` on the module objects, so this file must keep calling them
+through the module attribute (``glob.glob``, never ``from glob import
+glob``; ``shutil.which``, never ``from shutil import which``).
+"""
+
+from __future__ import annotations
+
+import glob
+import os
+import shutil
+import sys
+
+
+def _find_tesseract() -> str | None:
+    """Returns the tesseract executable path or None if not found."""
+    found = shutil.which("tesseract")
+    if found:
+        return found
+    if sys.platform == "win32":
+        candidates = [
+            r"C:\Program Files\Tesseract-OCR\tesseract.exe",
+            r"C:\Program Files (x86)\Tesseract-OCR\tesseract.exe",
+        ]
+    elif sys.platform == "darwin":
+        candidates = [
+            "/opt/homebrew/bin/tesseract",
+            "/usr/local/bin/tesseract",
+        ]
+    else:
+        candidates = [
+            "/usr/bin/tesseract",
+            "/usr/local/bin/tesseract",
+            "/snap/bin/tesseract",
+        ]
+    for p in candidates:
+        if os.path.isfile(p):
+            return p
+    return None
+
+
+def _newest_versioned_tessdata(pattern: str) -> str | None:
+    """First existing directory matched by *pattern*, reverse-sorted so the
+    newest ``tesseract-ocr/<version>`` wins."""
+    for p in sorted(glob.glob(pattern), reverse=True):
+        if os.path.isdir(p):
+            return p
+    return None
+
+
+def _find_tessdata(tess_exe: str | None) -> str | None:
+    """Locate the tessdata directory across platforms.
+
+    Precedence (first match wins):
+
+    1. ``<bindir>/tessdata`` adjacent to the binary: Windows and any
+       install that bundles the data next to the executable.
+    2. The versioned Debian layout under the binary's own prefix,
+       ``<prefix>/share/tesseract-ocr/<version>/tessdata``, newest first.
+       This is how the snap ships Tesseract: the binary is
+       ``$SNAP/usr/bin/tesseract`` (from the Ubuntu 22.04 ``tesseract-ocr``
+       deb) but its compiled-in default is the absolute
+       ``/usr/share/tesseract-ocr/4.00/tessdata``, which resolves against
+       the base snap's rootfs, where no Tesseract data is installed.
+       Without this step OCR in the snap failed with 'Error opening data
+       file /usr/share/tesseract-ocr/4.00/tessdata/eng.traineddata'. Deriving
+       from the binary instead of hard-coding ``$SNAP`` or ``4.00`` keeps
+       working when the snap moves to a newer base (the Tesseract 5 debs
+       ship ``.../tesseract-ocr/5/tessdata``), and only ever pairs a binary
+       with the data installed alongside it. For ``/usr/bin/tesseract``
+       it is the same lookup as step 3.
+    3. The versioned system layout
+       ``/usr/share/tesseract-ocr/<version>/tessdata``, newest first, for
+       a binary that lives outside ``/usr``. Checked *before* the flat
+       prefix derivation (step 4) on purpose: the binary often has a
+       stale default baked in (Ubuntu 24.04 ships v5 but still points at
+       .../4.00/tessdata, see issue #27), and a flat
+       ``/usr/share/tessdata``, which step 4 would derive from
+       ``/usr/bin/tesseract``, must never shadow a newer versioned
+       directory.
+    4. ``<prefix>/share/tessdata`` derived relative to the binary
+       (``<prefix>/bin/tesseract`` -> ``<prefix>/share/tessdata``). This
+       covers Homebrew (Intel ``/usr/local``, Apple Silicon
+       ``/opt/homebrew``) and non-standard install prefixes; on those
+       systems the versioned globs in steps 2 and 3 find nothing so we
+       land here.
+    5. Fixed fallbacks for older Debian, manual installs, Homebrew and
+       snap layouts.
+
+    Without TESSDATA_PREFIX set explicitly, OCR would otherwise fail with
+    'Error opening data file .../4.00/tessdata/eng.traineddata'."""
+    unix_like = sys.platform.startswith(("linux", "darwin"))
+    prefix = (os.path.dirname(os.path.dirname(tess_exe))
+              if tess_exe else None)
+    # 1. tessdata adjacent to the binary (Windows and bundled installs).
+    if tess_exe:
+        adjacent = os.path.join(os.path.dirname(tess_exe), "tessdata")
+        if os.path.isdir(adjacent):
+            return adjacent
+    # 2. Versioned layout under the binary's own prefix (the snap's
+    #    $SNAP/usr/share/tesseract-ocr/<version>/tessdata). glob.escape so
+    #    a prefix containing [ ] * ? is matched literally.
+    if unix_like and prefix:
+        found = _newest_versioned_tessdata(os.path.join(
+            glob.escape(prefix), "share", "tesseract-ocr", "*", "tessdata"))
+        if found:
+            return found
+    # 3. Versioned Linux layout, newest first. Kept ahead of the relative
+    #    prefix derivation so a stale /usr/share/tessdata never shadows a
+    #    newer /usr/share/tesseract-ocr/<version>/tessdata (issue #27).
+    if unix_like:
+        found = _newest_versioned_tessdata(
+            "/usr/share/tesseract-ocr/*/tessdata")
+        if found:
+            return found
+    # 4. Homebrew (Intel /usr/local, Apple Silicon /opt/homebrew) and
+    #    custom prefixes: <prefix>/bin/tesseract -> <prefix>/share/tessdata.
+    if prefix is not None:
+        prefixed = os.path.join(prefix, "share", "tessdata")
+        if os.path.isdir(prefixed):
+            return prefixed
+    # 5. Older Debian, manual installs, Homebrew (Intel + Apple Silicon),
+    #    snap fallbacks.
+    if unix_like:
+        for p in ("/usr/share/tessdata",
+                  "/usr/local/share/tessdata",
+                  "/opt/homebrew/share/tessdata",
+                  "/snap/tesseract/current/usr/share/tesseract-ocr/tessdata"):
+            if os.path.isdir(p):
+                return p
+    return None

app/tools/ocr.py

@@ -17,93 +17,9 @@
 from app.worker import TaskRunner, run_task
 from app.constants import TEXT_SEC, DESKTOP
 from app.widgets import DropFileEdit
-
-
-def _find_tesseract() -> str | None:
-    """Returns the tesseract executable path or None if not found."""
-    import shutil, sys
-    found = shutil.which("tesseract")
-    if found:
-        return found
-    if sys.platform == "win32":
-        candidates = [
-            r"C:\Program Files\Tesseract-OCR\tesseract.exe",
-            r"C:\Program Files (x86)\Tesseract-OCR\tesseract.exe",
-        ]
-    elif sys.platform == "darwin":
-        candidates = [
-            "/opt/homebrew/bin/tesseract",
-            "/usr/local/bin/tesseract",
-        ]
-    else:
-        candidates = [
-            "/usr/bin/tesseract",
-            "/usr/local/bin/tesseract",
-            "/snap/bin/tesseract",
-        ]
-    for p in candidates:
-        if os.path.isfile(p):
-            return p
-    return None
-
-
-def _find_tessdata(tess_exe: str | None) -> str | None:
-    """Locate the tessdata directory across platforms.
-
-    Precedence (first match wins):
-
-    1. ``<bindir>/tessdata`` adjacent to the binary — Windows and any
-       install that bundles the data next to the executable.
-    2. The versioned Linux layout
-       ``/usr/share/tesseract-ocr/<version>/tessdata``, reverse-sorted so
-       the newest version wins. Checked *before* the relative prefix
-       derivation (step 3) on purpose: the binary often has a stale
-       default baked in (Ubuntu 24.04 ships v5 but still points at
-       .../4.00/tessdata, see issue #27), and a flat ``/usr/share/tessdata``
-       — which step 3 would derive from ``/usr/bin/tesseract`` — must never
-       shadow a newer versioned directory.
-    3. ``<prefix>/share/tessdata`` derived relative to the binary
-       (``<prefix>/bin/tesseract`` -> ``<prefix>/share/tessdata``). This
-       covers Homebrew (Intel ``/usr/local``, Apple Silicon
-       ``/opt/homebrew``) and non-standard install prefixes; on those
-       systems the versioned glob in step 2 finds nothing so we land here.
-    4. Fixed fallbacks for older Debian, manual installs, Homebrew and
-       snap layouts.
-
-    Without TESSDATA_PREFIX set explicitly, OCR would otherwise fail with
-    'Error opening data file .../4.00/tessdata/eng.traineddata'."""
-    import sys
-    # 1. tessdata adjacent to the binary (Windows and bundled installs).
-    if tess_exe:
-        adjacent = os.path.join(os.path.dirname(tess_exe), "tessdata")
-        if os.path.isdir(adjacent):
-            return adjacent
-    # 2. Versioned Linux layout, newest first. Kept ahead of the relative
-    #    prefix derivation so a stale /usr/share/tessdata never shadows a
-    #    newer /usr/share/tesseract-ocr/<version>/tessdata (issue #27).
-    if sys.platform.startswith(("linux", "darwin")):
-        import glob
-        for p in sorted(glob.glob("/usr/share/tesseract-ocr/*/tessdata"),
-                        reverse=True):
-            if os.path.isdir(p):
-                return p
-    # 3. Homebrew (Intel /usr/local, Apple Silicon /opt/homebrew) and
-    #    custom prefixes: <prefix>/bin/tesseract -> <prefix>/share/tessdata.
-    if tess_exe:
-        prefixed = os.path.join(os.path.dirname(os.path.dirname(tess_exe)),
-                                "share", "tessdata")
-        if os.path.isdir(prefixed):
-            return prefixed
-    # 4. Older Debian, manual installs, Homebrew (Intel + Apple Silicon),
-    #    snap fallbacks.
-    if sys.platform.startswith(("linux", "darwin")):
-        for p in ("/usr/share/tessdata",
-                  "/usr/local/share/tessdata",
-                  "/opt/homebrew/share/tessdata",
-                  "/snap/tesseract/current/usr/share/tesseract-ocr/tessdata"):
-            if os.path.isdir(p):
-                return p
-    return None
+# Looked up through this module's globals by _ensure_tesseract, and imported
+# from here by tests: keep the names bound in app.tools.ocr.
+from app.tools._ocr_paths import _find_tessdata, _find_tesseract
 
 
 class TabOCR(BasePage):