Simplify missing source cov levels on cmd line warning

Instead of listing all possible source coverage combinations, express
them as a regular expression.

Author: Viviane Garèse

tools/gnatcov/command_line.ads

@@ -699,7 +699,7 @@ package Command_Line is
             & "  " & Object_Level_Options (Separator => ", ")
             & " (object coverage)"
             & ASCII.LF
-            & "  " & Source_Level_Options (Separator => ", ")
+            & "  " & Source_Level_Options
             & " (source coverage)"
             & ASCII.LF
             & "For the ""instrument"" command, "

tools/gnatcov/coverage_options.adb

@@ -119,9 +119,19 @@ package body Coverage_Options is
    -- Source_Level_Options --
    --------------------------
 
-   function Source_Level_Options (Separator : String) return String is
+   function Source_Level_Options return String is
+      function Level_Str (L : Source_Coverage_Level) return String;
+      --  Return the lowercase string representation of L
+
+      function Level_Str (L : Source_Coverage_Level) return String
+        is (To_Lower (L'Img));
    begin
-      return Level_Options (Source_Levels_Option_Map, Separator);
+      return Level_Str (Stmt)
+        & "(+" & Level_Str (Decision) & "|"
+        & "+"  & Level_Str (MCDC)     & "|"
+        & "+"  & Level_Str (UC_MCDC)  & ")?"
+        & "(+" & Level_Str (ATC)      & "|"
+        & "+"  & Level_Str (ATCC)     & ")?";
    end Source_Level_Options;
 
    -------------------------------------

tools/gnatcov/coverage_options.ads

@@ -69,9 +69,9 @@ package Coverage_Options is
    function Coverage_Option_Value (L : Levels_Type) return String;
    --  Return the coverage option value corresponding to L
 
-   function Source_Level_Options (Separator : String) return String;
-   --  Return a string expression listing the valid --level alternatives
-   --  for source coverage, separated by Separator.
+   function Source_Level_Options return String;
+   --  Return a regular expression string describing the valid --level
+   --  combinations of source coverage levels.
 
    function Object_Level_Options (Separator : String) return String;
    --  Return a string expression describing valid --level alternatives

tools/gnatcov/gnatcov_bits_specific.adb

@@ -1067,12 +1067,12 @@ procedure GNATcov_Bits_Specific is
                Fatal_Error
                  ("Instrumentation requires a source coverage level"
                   & ASCII.LF
-                  & "  (--level=" & Source_Level_Options ("|") & ")");
+                  & "  (--level=" & Source_Level_Options & ")");
             elsif not Source_Coverage_Enabled then
                Warn
                  ("Coverage level not specified on the command"
                   & " line or in the project file (--level="
-                  & Source_Level_Options ("|") & "), defaulting to ""stmt"".");
+                  & Source_Level_Options & "), defaulting to ""stmt"".");
                Set_Coverage_Levels ("stmt");
             end if;
 
@@ -1774,7 +1774,7 @@ begin
          if not (Source_Coverage_Enabled or else Object_Coverage_Enabled)
          then
             Warn ("Coverage level not specified on the command line or in the"
-                  & " project file (--level=" & Source_Level_Options ("|")
+                  & " project file (--level=" & Source_Level_Options
                   & "|" & Object_Level_Options ("|") & "), defaulting to"
                   & " ""stmt"".");
             Set_Coverage_Levels ("stmt");
@@ -1789,7 +1789,7 @@ begin
                  ("""report"" output format (from --annotate) is"
                     & " only for source coverage criteria"
                     & ASCII.LF
-                    & "  (--level=" & Source_Level_Options ("|")
+                    & "  (--level=" & Source_Level_Options
                     & ", not --level="
                     & Coverage_Option_Value (Current_Levels) & ")");