[Ada] Style checks on invalid UTF character cause crash

2020-06-19  Justin Squirek  <squirek@adacore.com>

gcc/ada/

	* widechar.adb, widechar.ads (Skip_Wide): Catch validity check
	failure when skipping over characters, and update comment to
	reflect Skip_Wide's usage in error printing.

gcc/ada/widechar.adb

@@ -203,7 +203,16 @@ package body Widechar is
    --  Start of processing for Skip_Wide
 
    begin
-      Discard := WC_Skip (Skip_Char, Wide_Character_Encoding_Method);
+      --  Capture invalid wide characters errors since we are going to discard
+      --  the result anyway. We just want to move past it.
+
+      begin
+         Discard := WC_Skip (Skip_Char, Wide_Character_Encoding_Method);
+      exception
+         when Constraint_Error =>
+            null;
+      end;
+
       Wide_Char_Byte_Count := Wide_Char_Byte_Count + Nat (P - P_Init - 1);
    end Skip_Wide;
 
@@ -235,7 +244,16 @@ package body Widechar is
    --  Start of processing for Skip_Wide
 
    begin
-      Discard := WC_Skip (Skip_Char, Wide_Character_Encoding_Method);
+      --  Capture invalid wide characters errors since we are going to discard
+      --  the result anyway. We just want to move past it.
+
+      begin
+         Discard := WC_Skip (Skip_Char, Wide_Character_Encoding_Method);
+      exception
+         when Constraint_Error =>
+            null;
+      end;
+
       Wide_Char_Byte_Count := Wide_Char_Byte_Count + Nat (P - P_Init - 1);
    end Skip_Wide;
 

gcc/ada/widechar.ads

@@ -81,9 +81,7 @@ package Widechar is
    --  On entry, S (P) points to an ESC character for a wide character escape
    --  sequence or to an upper half character if the encoding method uses the
    --  upper bit, or to a left bracket if the brackets encoding method is in
-   --  use. On exit, P is bumped past the wide character sequence. No error
-   --  checking is done, since this is only used on escape sequences generated
-   --  by Set_Wide, which are known to be correct.
+   --  use. On exit, P is bumped past the wide character sequence.
 
    procedure Skip_Wide (S : Source_Buffer_Ptr; P : in out Source_Ptr);
    --  Similar to the above procedure, but operates on a source buffer