[Ada] Spurious error in nested generic containing expression function

[Pierre-Marie de Rodat]

This patch removes spurious visibility errors from the instantiation of a
generic package nested within another generic, when the inner package
contains an expression function that is the completion of a visible
function of that package, and the expression includes an object of a
tagged type local to the generic.

No small example available.

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

2017-09-29  Ed Schonberg  <schonb...@adacore.com>

        * sem_ch6.adb (Analyze_Expression_Function): Do not emit freeze nodes
        for types in expression if the function is within a generic unit.
        * sem_res.adb (Resolve): In a generic context do not freeze an
        expression, unless it is an entity. This exception is solely for the
        purpose of detecting illegal uses of deferred constants in generic
        units.
        * sem_res.adb: Minor reformatting.


Index: sem_ch6.adb
===================================================================
--- sem_ch6.adb (revision 253283)
+++ sem_ch6.adb (working copy)
@@ -568,8 +568,11 @@
          --  Note that we cannot defer this freezing to the analysis of the
          --  expression itself, because a freeze node might appear in a nested
          --  scope, leading to an elaboration order issue in gigi.
+         --  As elsewhere, we do not emit freeze nodes within a generic unit.
 
-         Freeze_Expr_Types (Def_Id);
+         if not Inside_A_Generic then
+            Freeze_Expr_Types (Def_Id);
+         end if;
 
          --  For navigation purposes, indicate that the function is a body
 
Index: sem_res.adb
===================================================================
--- sem_res.adb (revision 253283)
+++ sem_res.adb (working copy)
@@ -3070,8 +3070,15 @@
          --  Here we are resolving the corresponding expanded body, so we do
          --  need to perform normal freezing.
 
-         Freeze_Expression (N);
+         --  As elsewhere we do not emit freeze node within a generic. We make
+         --  an exception for entities that are expressions, only to detect
+         --  misuses of deferred constants and preserve the output of various
+         --  tests.
 
+         if not Inside_A_Generic or else Is_Entity_Name (N) then
+            Freeze_Expression (N);
+         end if;
+
          --  Now we can do the expansion
 
          Expand (N);