[Ada] Give missing entity messages in -gnatc mode

[Arnaud Charlet]

This patch forces expansion on (but not actual code generation) for
configurable run time mode or no run time mode in -gnatc mode. This
means that we get error messages about unsupported features even in
-gnatc mode, which was not true before. The following is compiled
in -gnatc mode with a gnat.adc file containing pragma No_Run_Time:

     1. function CRT_GNATC (X : Integer) return Integer is
     2. begin
     3.    return X ** X;
                    |
        >>> construct not allowed in no run time mode
        >>> entity "System.Exp_Int.Exp_Integer" not defined

     4. end;

prior to this patch, no message was given in -gnatc mode. A debug
flag -gnatd.Z can be used to disable this behavior in case we run
into any trouble from doing the expansion in the future.

Tested on x86_64-pc-linux-gnu, committed on trunk

2014-08-01  Robert Dewar  <dewar@adacore.com>

	* debug.adb: Document debug switch -gnatd.Z.
	* sem.adb (Semantics): Force expansion on in no or configurable
	run time mode.

-------------- next part --------------
Index: debug.adb
===================================================================
--- debug.adb	(revision 213453)
+++ debug.adb	(working copy)
@@ -143,7 +143,7 @@
    --  d.W  Print out debugging information for Walk_Library_Items
    --  d.X  Old treatment of indexing aspects
    --  d.Y
-   --  d.Z
+   --  d.Z  Do not enable expansion in configurable run-time mode
 
    --  d1   Error msgs have node numbers where possible
    --  d2   Eliminate error flags in verbose form error messages
@@ -686,6 +686,12 @@
    --       is preserved temporarily for use by the modelling project under
    --       debug flag d.X.
 
+   --  d.Z  Normally we always enable expansion in configurable run-time mode
+   --       to make sure we get error messages about unsupported features even
+   --       when compiling in -gnatc mode. But expansion is turned off in this
+   --       case if debug flag -gnatd.Z is used. This is to deal with the case
+   --       where we discover difficulties in this new processing.
+
    --  d1   Error messages have node numbers where possible. Normally error
    --       messages have only source locations. This option is useful when
    --       debugging errors caused by expanded code, where the source location
Index: sem.adb
===================================================================
--- sem.adb	(revision 213437)
+++ sem.adb	(working copy)
@@ -1410,11 +1410,33 @@
          GNAT_Mode := True;
       end if;
 
+      --  For generic main, never do expansion
+
       if Generic_Main then
          Expander_Mode_Save_And_Set (False);
+
+      --  Non generic case
+
       else
          Expander_Mode_Save_And_Set
-           (Operating_Mode = Generate_Code or Debug_Flag_X);
+
+           --  Turn on expansion if generating code
+
+           (Operating_Mode = Generate_Code
+
+             --  or if special debug flag -gnatdx is set
+
+             or else Debug_Flag_X
+
+             --  Or if in configuration run-time mode. We do this so we get
+             --  error messages about missing entities in the run-time even
+             --  if we are compiling in -gnatc (no code generation) mode.
+             --  Similar processing applies to No_Run_Time_Mode. However,
+             --  don't do this if debug flag -gnatd.Z is set (this is to handle
+             --  a situation where this new processing causes trouble).
+
+             or else ((Configurable_Run_Time_Mode or No_Run_Time_Mode)
+                       and not Debug_Flag_Dot_ZZ));
       end if;
 
       Full_Analysis      := True;