1 ------------------------------------------------------------------------------
3 -- GNAT COMPILER COMPONENTS --
9 -- Copyright (C) 1992-2010, Free Software Foundation, Inc. --
11 -- GNAT is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
17 -- for more details. You should have received a copy of the GNU General --
18 -- Public License distributed with GNAT; see file COPYING3. If not, go to --
19 -- http://www.gnu.org/licenses for a complete copy of the license. --
21 -- GNAT was originally developed by the GNAT team at New York University. --
22 -- Extensive contributions were provided by Ada Core Technologies Inc. --
24 ------------------------------------------------------------------------------
26 with Atree; use Atree;
27 with Debug; use Debug;
28 with Einfo; use Einfo;
29 with Errout; use Errout;
30 with Fname; use Fname;
31 with Fname.UF; use Fname.UF;
32 with Nlists; use Nlists;
33 with Nmake; use Nmake;
35 with Osint; use Osint;
36 with Osint.C; use Osint.C;
37 with Output; use Output;
39 with Restrict; use Restrict;
41 with Sinfo; use Sinfo;
42 with Sinput; use Sinput;
43 with Sinput.L; use Sinput.L;
44 with Stand; use Stand;
45 with Tbuild; use Tbuild;
46 with Uname; use Uname;
48 package body Lib.Load is
50 -----------------------
51 -- Local Subprograms --
52 -----------------------
54 function From_Limited_With_Chain return Boolean;
55 -- Check whether a possible circular dependence includes units that
56 -- have been loaded through limited_with clauses, in which case there
57 -- is no real circularity.
59 function Spec_Is_Irrelevant
60 (Spec_Unit : Unit_Number_Type;
61 Body_Unit : Unit_Number_Type) return Boolean;
62 -- The Spec_Unit and Body_Unit parameters are the unit numbers of the
63 -- spec file that corresponds to the main unit which is a body. This
64 -- function determines if the spec file is irrelevant and will be
65 -- overridden by the body as described in RM 10.1.4(4). See description
66 -- in "Special Handling of Subprogram Bodies" for further details.
68 procedure Write_Dependency_Chain;
69 -- This procedure is used to generate error message info lines that
70 -- trace the current dependency chain when a load error occurs.
72 ------------------------------
73 -- Change_Main_Unit_To_Spec --
74 ------------------------------
76 procedure Change_Main_Unit_To_Spec is
77 U : Unit_Record renames Units.Table (Main_Unit);
79 X : Source_File_Index;
82 -- Get name of unit body
84 Get_Name_String (U.Unit_File_Name);
86 -- Note: for the following we should really generalize and consult the
87 -- file name pattern data, but for now we just deal with the common
88 -- naming cases, which is probably good enough in practice ???
90 -- Change .adb to .ads
93 and then Name_Buffer (Name_Len - 3 .. Name_Len) = ".adb"
95 Name_Buffer (Name_Len) := 's';
97 -- Change .2.ada to .1.ada (Rational convention)
100 and then Name_Buffer (Name_Len - 5 .. Name_Len) = ".2.ada"
102 Name_Buffer (Name_Len - 4) := '1';
104 -- Change .ada to _.ada (DEC convention)
107 and then Name_Buffer (Name_Len - 3 .. Name_Len) = ".ada"
109 Name_Buffer (Name_Len - 3 .. Name_Len + 1) := "_.ada";
110 Name_Len := Name_Len + 1;
112 -- No match, don't make the change
118 -- Try loading the spec
121 X := Load_Source_File (N);
123 -- No change if we did not find the spec
125 if X = No_Source_File then
129 -- Otherwise modify Main_Unit entry to point to spec
131 U.Unit_File_Name := N;
133 end Change_Main_Unit_To_Spec;
135 -------------------------------
136 -- Create_Dummy_Package_Unit --
137 -------------------------------
139 function Create_Dummy_Package_Unit
140 (With_Node : Node_Id;
141 Spec_Name : Unit_Name_Type) return Unit_Number_Type
143 Unum : Unit_Number_Type;
144 Cunit_Entity : Entity_Id;
146 Du_Name : Node_Or_Entity_Id;
148 Save_CS : constant Boolean := Get_Comes_From_Source_Default;
151 -- The created dummy package unit does not come from source
153 Set_Comes_From_Source_Default (False);
157 if Nkind (Name (With_Node)) = N_Identifier then
159 Make_Defining_Identifier (No_Location,
160 Chars => Chars (Name (With_Node)));
161 Du_Name := Cunit_Entity;
162 End_Lab := New_Occurrence_Of (Cunit_Entity, No_Location);
168 Make_Defining_Identifier (No_Location,
169 Chars => Chars (Selector_Name (Name (With_Node))));
171 Make_Defining_Program_Unit_Name (No_Location,
172 Name => Copy_Separate_Tree (Prefix (Name (With_Node))),
173 Defining_Identifier => Cunit_Entity);
175 Set_Is_Child_Unit (Cunit_Entity);
178 Make_Designator (No_Location,
179 Name => Copy_Separate_Tree (Prefix (Name (With_Node))),
180 Identifier => New_Occurrence_Of (Cunit_Entity, No_Location));
183 Set_Scope (Cunit_Entity, Standard_Standard);
186 Make_Compilation_Unit (No_Location,
187 Context_Items => Empty_List,
189 Make_Package_Declaration (No_Location,
191 Make_Package_Specification (No_Location,
192 Defining_Unit_Name => Du_Name,
193 Visible_Declarations => Empty_List,
194 End_Label => End_Lab)),
196 Make_Compilation_Unit_Aux (No_Location));
198 -- Mark the dummy package as analyzed to prevent analysis of this
199 -- (non-existent) unit in -gnatQ mode because at the moment the
200 -- structure and attributes of this dummy package does not allow
201 -- a normal analysis of this unit
203 Set_Analyzed (Cunit);
205 Units.Increment_Last;
208 Units.Table (Unum) := (
210 Cunit_Entity => Cunit_Entity,
212 Dynamic_Elab => False,
213 Error_Location => Sloc (With_Node),
214 Expected_Unit => Spec_Name,
216 Generate_Code => False,
218 Is_Compiler_Unit => False,
219 Ident_String => Empty,
221 Main_Priority => Default_Main_Priority,
224 Source_Index => No_Source_File,
225 Unit_File_Name => Get_File_Name (Spec_Name, Subunit => False),
226 Unit_Name => Spec_Name,
230 Set_Comes_From_Source_Default (Save_CS);
231 Set_Error_Posted (Cunit_Entity);
232 Set_Error_Posted (Cunit);
234 end Create_Dummy_Package_Unit;
236 -----------------------------
237 -- From_Limited_With_Chain --
238 -----------------------------
240 function From_Limited_With_Chain return Boolean is
241 Curr_Num : constant Unit_Number_Type :=
242 Load_Stack.Table (Load_Stack.Last).Unit_Number;
245 -- True if the current load operation is through a limited_with clause
246 -- and we are not within a loop of regular with_clauses.
248 for U in reverse Load_Stack.First .. Load_Stack.Last - 1 loop
249 if Load_Stack.Table (U).Unit_Number = Curr_Num then
252 elsif Present (Load_Stack.Table (U).With_Node)
253 and then Limited_Present (Load_Stack.Table (U).With_Node)
260 end From_Limited_With_Chain;
266 procedure Initialize is
272 ------------------------
273 -- Initialize_Version --
274 ------------------------
276 procedure Initialize_Version (U : Unit_Number_Type) is
278 Units.Table (U).Version := Source_Checksum (Source_Index (U));
279 end Initialize_Version;
281 ----------------------
282 -- Load_Main_Source --
283 ----------------------
285 procedure Load_Main_Source is
286 Fname : File_Name_Type;
290 Load_Stack.Increment_Last;
291 Load_Stack.Table (Load_Stack.Last) := (Main_Unit, Empty);
293 -- Initialize unit table entry for Main_Unit. Note that we don't know
294 -- the unit name yet, that gets filled in when the parser parses the
295 -- main unit, at which time a check is made that it matches the main
296 -- file name, and then the Unit_Name field is set. The Cunit and
297 -- Cunit_Entity fields also get filled in later by the parser.
299 Units.Increment_Last;
300 Fname := Next_Main_Source;
302 Units.Table (Main_Unit).Unit_File_Name := Fname;
304 if Fname /= No_File then
305 Main_Source_File := Load_Source_File (Fname);
306 Current_Error_Source_File := Main_Source_File;
308 if Main_Source_File /= No_Source_File then
309 Version := Source_Checksum (Main_Source_File);
312 Units.Table (Main_Unit) := (
314 Cunit_Entity => Empty,
316 Dynamic_Elab => False,
317 Error_Location => No_Location,
318 Expected_Unit => No_Unit_Name,
319 Fatal_Error => False,
320 Generate_Code => False,
322 Is_Compiler_Unit => False,
323 Ident_String => Empty,
325 Main_Priority => Default_Main_Priority,
328 Source_Index => Main_Source_File,
329 Unit_File_Name => Fname,
330 Unit_Name => No_Unit_Name,
334 end Load_Main_Source;
341 (Load_Name : Unit_Name_Type;
343 Error_Node : Node_Id;
345 Corr_Body : Unit_Number_Type := No_Unit;
346 Renamings : Boolean := False;
347 With_Node : Node_Id := Empty) return Unit_Number_Type
349 Calling_Unit : Unit_Number_Type;
350 Uname_Actual : Unit_Name_Type;
351 Unum : Unit_Number_Type;
352 Unump : Unit_Number_Type;
353 Fname : File_Name_Type;
354 Src_Ind : Source_File_Index;
356 -- Start of processing for Load_Unit
359 -- If renamings are allowed and we have a child unit name, then we
360 -- must first load the parent to deal with finding the real name.
361 -- Retain the with_clause that names the child, so that if it is
362 -- limited, the parent is loaded under the same condition.
364 if Renamings and then Is_Child_Name (Load_Name) then
367 (Load_Name => Get_Parent_Spec_Name (Load_Name),
368 Required => Required,
371 Error_Node => Error_Node,
372 With_Node => With_Node);
374 if Unump = No_Unit then
378 -- If parent is a renaming, then we use the renamed package as
379 -- the actual parent for the subsequent load operation.
381 if Nkind (Unit (Cunit (Unump))) = N_Package_Renaming_Declaration then
384 (Load_Name, Get_Unit_Name (Name (Unit (Cunit (Unump)))));
386 -- Save the renaming entity, to establish its visibility when
387 -- installing the context. The implicit with is on this entity,
388 -- not on the package it renames.
390 if Nkind (Error_Node) = N_With_Clause
391 and then Nkind (Name (Error_Node)) = N_Selected_Component
394 Par : Node_Id := Name (Error_Node);
397 while Nkind (Par) = N_Selected_Component
398 and then Chars (Selector_Name (Par)) /=
399 Chars (Cunit_Entity (Unump))
404 -- Case of some intermediate parent is a renaming
406 if Nkind (Par) = N_Selected_Component then
407 Set_Entity (Selector_Name (Par), Cunit_Entity (Unump));
409 -- Case where the ultimate parent is a renaming
412 Set_Entity (Par, Cunit_Entity (Unump));
417 -- If the parent is not a renaming, then get its name (this may
418 -- be different from the parent spec name obtained above because
419 -- of renamings higher up in the hierarchy).
422 Uname_Actual := New_Child (Load_Name, Unit_Name (Unump));
425 -- Here if unit to be loaded is not a child unit
428 Uname_Actual := Load_Name;
431 Fname := Get_File_Name (Uname_Actual, Subunit);
435 Write_Str ("*** Load request for unit: ");
436 Write_Unit_Name (Load_Name);
439 Write_Str (" (Required = True)");
441 Write_Str (" (Required = False)");
446 if Uname_Actual /= Load_Name then
447 Write_Str ("*** Actual unit loaded: ");
448 Write_Unit_Name (Uname_Actual);
452 -- Capture error location if it is for the main unit. The idea is to
453 -- post errors on the main unit location, not the most recent unit.
454 -- Note: Unit_Name (Main_Unit) is not set if we are parsing gnat.adc.
456 if Present (Error_Node)
457 and then Unit_Name (Main_Unit) /= No_Unit_Name
459 -- It seems like In_Extended_Main_Source_Unit (Error_Node) would
460 -- do the trick here, but that's wrong, it is much too early to
461 -- call this routine. We are still in the parser, and the required
462 -- semantic information is not established yet. So we base the
463 -- judgment on unit names.
465 Get_External_Unit_Name_String (Unit_Name (Main_Unit));
468 Main_Unit_Name : constant String := Name_Buffer (1 .. Name_Len);
471 Get_External_Unit_Name_String
472 (Unit_Name (Get_Source_Unit (Error_Node)));
474 -- If the two names are identical, then for sure we are part
475 -- of the extended main unit
477 if Main_Unit_Name = Name_Buffer (1 .. Name_Len) then
478 Load_Msg_Sloc := Sloc (Error_Node);
480 -- If the load is called from a with_type clause, the error
483 -- Otherwise, check for the subunit case, and if so, consider
484 -- we have a match if one name is a prefix of the other name.
487 if Nkind (Unit (Cunit (Main_Unit))) = N_Subunit
489 Nkind (Unit (Cunit (Get_Source_Unit (Error_Node)))) =
492 Name_Len := Integer'Min (Name_Len, Main_Unit_Name'Length);
494 if Name_Buffer (1 .. Name_Len)
496 Main_Unit_Name (1 .. Name_Len)
498 Load_Msg_Sloc := Sloc (Error_Node);
505 -- If we are generating error messages, then capture calling unit
507 if Present (Error_Node) then
508 Calling_Unit := Get_Source_Unit (Error_Node);
510 Calling_Unit := No_Unit;
513 -- See if we already have an entry for this unit
516 while Unum <= Units.Last loop
517 exit when Uname_Actual = Units.Table (Unum).Unit_Name;
521 -- Whether or not the entry was found, Unum is now the right value,
522 -- since it is one more than Units.Last (i.e. the index of the new
523 -- entry we will create) in the not found case.
525 -- A special check is necessary in the unit not found case. If the unit
526 -- is not found, but the file in which it lives has already been loaded,
527 -- then we have the problem that the file does not contain the unit that
528 -- is needed. We simply treat this as a file not found condition.
530 -- We skip this test in multiple unit per file mode since in this
531 -- case we can have multiple units from the same source file.
533 if Unum > Units.Last and then Get_Unit_Index (Uname_Actual) = 0 then
534 for J in Units.First .. Units.Last loop
535 if Fname = Units.Table (J).Unit_File_Name then
537 Write_Str (" file does not contain unit, Unit_Number = ");
538 Write_Int (Int (Unum));
543 if Present (Error_Node) then
544 if Is_Predefined_File_Name (Fname) then
545 Error_Msg_Unit_1 := Uname_Actual;
547 ("$$ is not a language defined unit", Load_Msg_Sloc);
549 Error_Msg_File_1 := Fname;
550 Error_Msg_Unit_1 := Uname_Actual;
551 Error_Msg ("File{ does not contain unit$", Load_Msg_Sloc);
554 Write_Dependency_Chain;
564 -- If we are proceeding with load, then make load stack entry,
565 -- and indicate the kind of with_clause responsible for the load.
567 Load_Stack.Increment_Last;
568 Load_Stack.Table (Load_Stack.Last) := (Unum, With_Node);
570 -- Case of entry already in table
572 if Unum <= Units.Last then
574 -- Here is where we check for a circular dependency, which is
575 -- an attempt to load a unit which is currently in the process
576 -- of being loaded. We do *not* care about a circular chain that
577 -- leads back to a body, because this kind of circular dependence
578 -- legitimately occurs (e.g. two package bodies that contain
579 -- inlined subprogram referenced by the other).
581 -- Ada 2005 (AI-50217): We also ignore limited_with clauses, because
582 -- their purpose is precisely to create legal circular structures.
585 and then (Is_Spec_Name (Units.Table (Unum).Unit_Name)
586 or else Acts_As_Spec (Units.Table (Unum).Cunit))
587 and then (Nkind (Error_Node) /= N_With_Clause
588 or else not Limited_Present (Error_Node))
589 and then not From_Limited_With_Chain
592 Write_Str (" circular dependency encountered");
596 if Present (Error_Node) then
597 Error_Msg ("circular unit dependency", Load_Msg_Sloc);
598 Write_Dependency_Chain;
600 Load_Stack.Decrement_Last;
607 Write_Str (" unit already in file table, Unit_Number = ");
608 Write_Int (Int (Unum));
612 Load_Stack.Decrement_Last;
615 -- Unit is not already in table, so try to open the file
619 Write_Str (" attempt unit load, Unit_Number = ");
620 Write_Int (Int (Unum));
624 Src_Ind := Load_Source_File (Fname);
626 -- Make a partial entry in the file table, used even in the file not
627 -- found case to print the dependency chain including the last entry
629 Units.Increment_Last;
630 Units.Table (Unum).Unit_Name := Uname_Actual;
634 if Src_Ind /= No_Source_File then
635 Units.Table (Unum) := (
637 Cunit_Entity => Empty,
639 Dynamic_Elab => False,
640 Error_Location => Sloc (Error_Node),
641 Expected_Unit => Uname_Actual,
642 Fatal_Error => False,
643 Generate_Code => False,
645 Is_Compiler_Unit => False,
646 Ident_String => Empty,
648 Main_Priority => Default_Main_Priority,
651 Source_Index => Src_Ind,
652 Unit_File_Name => Fname,
653 Unit_Name => Uname_Actual,
654 Version => Source_Checksum (Src_Ind),
657 -- Parse the new unit
660 Save_Index : constant Nat := Multiple_Unit_Index;
661 Save_PMS : constant Boolean := Parsing_Main_Subunit;
664 Multiple_Unit_Index := Get_Unit_Index (Uname_Actual);
665 Units.Table (Unum).Munit_Index := Multiple_Unit_Index;
666 Initialize_Scanner (Unum, Source_Index (Unum));
668 if Calling_Unit = Main_Unit and then Subunit then
669 Parsing_Main_Subunit := True;
672 Discard_List (Par (Configuration_Pragmas => False));
674 Parsing_Main_Subunit := Save_PMS;
676 Multiple_Unit_Index := Save_Index;
677 Set_Loading (Unum, False);
680 -- If spec is irrelevant, then post errors and quit
682 if Corr_Body /= No_Unit
683 and then Spec_Is_Irrelevant (Unum, Corr_Body)
685 Error_Msg_File_1 := Unit_File_Name (Corr_Body);
687 ("cannot compile subprogram in file {!", Load_Msg_Sloc);
688 Error_Msg_File_1 := Unit_File_Name (Unum);
690 ("\incorrect spec in file { must be removed first!",
695 -- If loaded unit had a fatal error, then caller inherits it!
697 if Units.Table (Unum).Fatal_Error
698 and then Present (Error_Node)
700 Units.Table (Calling_Unit).Fatal_Error := True;
703 -- Remove load stack entry and return the entry in the file table
705 Load_Stack.Decrement_Last;
707 -- All done, return unit number
711 -- Case of file not found
715 Write_Str (" file was not found, load failed");
719 -- Generate message if unit required
721 if Required and then Present (Error_Node) then
722 if Is_Predefined_File_Name (Fname) then
724 -- This is a predefined library unit which is not present
725 -- in the run time. If a predefined unit is not available
726 -- it may very likely be the case that there is also pragma
727 -- Restriction forbidding its usage. This is typically the
728 -- case when building a configurable run time, where the
729 -- usage of certain run-time units is restricted by means
730 -- of both the corresponding pragma Restriction (such as
731 -- No_Calendar), and by not including the unit. Hence, we
732 -- check whether this predefined unit is forbidden, so that
733 -- the message about the restriction violation is generated,
736 Check_Restricted_Unit (Load_Name, Error_Node);
738 Error_Msg_Unit_1 := Uname_Actual;
740 ("$$ is not a predefined library unit", Load_Msg_Sloc);
743 Error_Msg_File_1 := Fname;
744 Error_Msg ("file{ not found", Load_Msg_Sloc);
747 Write_Dependency_Chain;
749 -- Remove unit from stack, to avoid cascaded errors on
750 -- subsequent missing files.
752 Load_Stack.Decrement_Last;
753 Units.Decrement_Last;
755 -- If unit not required, remove load stack entry and the junk
756 -- file table entry, and return No_Unit to indicate not found,
759 Load_Stack.Decrement_Last;
760 Units.Decrement_Last;
768 --------------------------
769 -- Make_Child_Decl_Unit --
770 --------------------------
772 procedure Make_Child_Decl_Unit (N : Node_Id) is
773 Unit_Decl : constant Node_Id := Library_Unit (N);
776 Units.Increment_Last;
777 Units.Table (Units.Last) := Units.Table (Get_Cunit_Unit_Number (N));
778 Units.Table (Units.Last).Unit_Name :=
779 Get_Spec_Name (Unit_Name (Get_Cunit_Unit_Number (N)));
780 Units.Table (Units.Last).Cunit := Unit_Decl;
781 Units.Table (Units.Last).Cunit_Entity :=
783 (Defining_Unit_Name (Specification (Unit (Unit_Decl))));
785 -- The library unit created for of a child subprogram unit plays no
786 -- role in code generation and binding, so label it accordingly.
788 Units.Table (Units.Last).Generate_Code := False;
789 Set_Has_No_Elaboration_Code (Unit_Decl);
790 end Make_Child_Decl_Unit;
792 ------------------------
793 -- Make_Instance_Unit --
794 ------------------------
796 -- If the unit is an instance, it appears as a package declaration, but
797 -- contains both declaration and body of the instance. The body becomes
798 -- the main unit of the compilation, and the declaration is inserted
799 -- at the end of the unit table. The main unit now has the name of a
800 -- body, which is constructed from the name of the original spec,
801 -- and is attached to the compilation node of the original unit. The
802 -- declaration has been attached to a new compilation unit node, and
803 -- code will have to be generated for it.
805 procedure Make_Instance_Unit (N : Node_Id; In_Main : Boolean) is
806 Sind : constant Source_File_Index := Source_Index (Main_Unit);
809 Units.Increment_Last;
812 Units.Table (Units.Last) := Units.Table (Main_Unit);
813 Units.Table (Units.Last).Cunit := Library_Unit (N);
814 Units.Table (Units.Last).Generate_Code := True;
815 Units.Table (Main_Unit).Cunit := N;
816 Units.Table (Main_Unit).Unit_Name :=
818 (Unit_Name (Get_Cunit_Unit_Number (Library_Unit (N))));
819 Units.Table (Main_Unit).Version := Source_Checksum (Sind);
822 -- Duplicate information from instance unit, for the body. The unit
823 -- node N has been rewritten as a body, but it was placed in the
824 -- units table when first loaded as a declaration.
826 Units.Table (Units.Last) := Units.Table (Get_Cunit_Unit_Number (N));
827 Units.Table (Units.Last).Cunit := Library_Unit (N);
829 end Make_Instance_Unit;
831 ------------------------
832 -- Spec_Is_Irrelevant --
833 ------------------------
835 function Spec_Is_Irrelevant
836 (Spec_Unit : Unit_Number_Type;
837 Body_Unit : Unit_Number_Type) return Boolean
839 Sunit : constant Node_Id := Cunit (Spec_Unit);
840 Bunit : constant Node_Id := Cunit (Body_Unit);
843 -- The spec is irrelevant if the body is a subprogram body, and the spec
844 -- is other than a subprogram spec or generic subprogram spec. Note that
845 -- the names must be the same, we don't need to check that, because we
846 -- already know that from the fact that the file names are the same.
849 Nkind (Unit (Bunit)) = N_Subprogram_Body
850 and then Nkind (Unit (Sunit)) /= N_Subprogram_Declaration
851 and then Nkind (Unit (Sunit)) /= N_Generic_Subprogram_Declaration;
852 end Spec_Is_Irrelevant;
858 procedure Version_Update (U : Node_Id; From : Node_Id) is
859 Unum : constant Unit_Number_Type := Get_Cunit_Unit_Number (U);
860 Fnum : constant Unit_Number_Type := Get_Cunit_Unit_Number (From);
862 if Source_Index (Fnum) /= No_Source_File then
863 Units.Table (Unum).Version :=
864 Units.Table (Unum).Version
866 Source_Checksum (Source_Index (Fnum));
870 ----------------------------
871 -- Write_Dependency_Chain --
872 ----------------------------
874 procedure Write_Dependency_Chain is
876 -- The dependency chain is only written if it is at least two entries
877 -- deep, otherwise it is trivial (the main unit depending on a unit
878 -- that it obviously directly depends on).
880 if Load_Stack.Last - 1 > Load_Stack.First then
881 for U in Load_Stack.First .. Load_Stack.Last - 1 loop
883 Unit_Name (Load_Stack.Table (U).Unit_Number);
885 Unit_Name (Load_Stack.Table (U + 1).Unit_Number);
886 Error_Msg ("$ depends on $!", Load_Msg_Sloc);
889 end Write_Dependency_Chain;