Merge branch 'topic/robustness' into 'master'

Make scripts robust to liblktlang import failures

Closes #755

See merge request eng/libadalang/langkit!1000

Author: eliericha

langkit/compile_context.py

@@ -57,7 +57,16 @@
 
 try:
     import liblktlang as L
-except ImportError:
+except (ImportError, OSError):
+    # ImportError may be raised if liblktlang is not available.
+    #
+    # OSError may be raised if liblktlang is available, but the underlying
+    # dynamic library is missing dependency libraries. This can occur if the
+    # library was built with one version of the compiler, and then the compiler
+    # installation gets updated.  liblktlang has stale library links and fails
+    # to load.
+    #
+    # In both scenarios, assume liblktlang is not available and continue.
     pass
 
 

langkit/diagnostics.py

@@ -18,7 +18,16 @@
 liblktlang_available = True
 try:
     import liblktlang as L
-except ImportError:
+except (ImportError, OSError):
+    # ImportError may be raised if liblktlang is not available.
+    #
+    # OSError may be raised if liblktlang is available, but the underlying
+    # dynamic library is missing dependency libraries. This can occur if the
+    # library was built with one version of the compiler, and then the compiler
+    # installation gets updated.  liblktlang has stale library links and fails
+    # to load.
+    #
+    # In both scenarios, assume liblktlang is not available and continue.
     liblktlang_available = False