Instrument.C: avoid clobbering the Scopes_In_Files_Map

We were leaving erased file scopes in the Scopes_In_Files_Map which
resulted in a crash when calling multiple times Remap_Scopes on this
clobbered map. Fix this to leave it in a consistent state and properly
remove empty file scopes.

Author: Jugst3r

testsuite/tests/subp_of_interest_c/src/bar.h

@@ -0,0 +1,5 @@
+int
+bar ()
+{
+  return 0;
+}

testsuite/tests/subp_of_interest_c/src/main.c

@@ -0,0 +1,10 @@
+#include "bar.h"
+#include "pkg.h"
+
+int
+main ()
+{
+  foo ();
+  bar ();
+  return 0;
+}

testsuite/tests/subp_of_interest_c/src/pkg.c

@@ -0,0 +1,5 @@
+int
+foo ()
+{
+  return 0;
+}

testsuite/tests/subp_of_interest_c/src/pkg.h

@@ -0,0 +1 @@
+extern int foo ();

testsuite/tests/subp_of_interest_c/test.py

@@ -0,0 +1,41 @@
+"""
+Check that the subprograms of interest mechanism works as expected on a C
+example.
+"""
+
+import os
+import os.path
+
+from SCOV.minicheck import build_run_and_coverage, check_xcov_reports
+from SUITE.context import thistest
+from SUITE.cutils import contents_of, Wdir
+from SUITE.tutils import gprfor, xcov
+from SUITE.gprutils import GPRswitches
+
+tmp = Wdir("tmp_")
+
+cov_args = build_run_and_coverage(
+    gprsw=GPRswitches(
+        gprfor(srcdirs=os.path.join("..", "src"), mains=["main.c"])
+    ),
+    covlevel="stmt",
+    mains=["main"],
+    trace_mode='src',
+    extra_coverage_args=[
+        "-axcov",
+        "--subprograms",
+        f"{os.path.join('..', 'src', 'pkg.c')}:1",
+    ],
+)
+
+check_xcov_reports(
+    "*.xcov",
+    {
+        "main.c.xcov": {},
+        "bar.h.xcov": {},
+        "pkg.c.xcov": {"+": {4}},
+    },
+    "obj",
+)
+
+thistest.result()

tools/gnatcov/instrument-c.adb

@@ -150,6 +150,8 @@ package body Instrument.C is
    --  Convert low level SCOs in each scope for each file to high-level SCOs
    --  using the mapping in SCO_Map. Set the file's SCO range to cover all of
    --  its scopes' SCO ranges.
+   --
+   --  Also remove from the Scopes map empty file scopes.
 
    overriding procedure Append_SCO
      (Pass               : Instrument_Pass_Kind;
@@ -491,10 +493,6 @@ package body Instrument.C is
       UIC  : in out C_Unit_Inst_Context'Class;
       N    : Cursor_T)
    is
-      Inserted : Boolean;
-
-      File_Scope_Position : Scopes_In_Files_Map.Cursor;
-
       procedure Enter_File_Scope
         (UIC : in out C_Unit_Inst_Context'Class;
          SFI : Source_File_Index)
@@ -508,7 +506,11 @@ package body Instrument.C is
 
       procedure Enter_File_Scope
         (UIC : in out C_Unit_Inst_Context'Class;
-         SFI : Source_File_Index) is
+         SFI : Source_File_Index)
+      is
+         File_Scope_Position : Scopes_In_Files_Map.Cursor;
+
+         Inserted : Boolean;
       begin
          if not UIC.Scopes.Contains (SFI) then
 
@@ -629,24 +631,26 @@ package body Instrument.C is
 
    procedure Remap_Scopes
      (Scopes  : in out Scopes_In_Files_Map.Map;
-      SCO_Map : LL_HL_SCO_Map) is
+      SCO_Map : LL_HL_SCO_Map)
+   is
+      Res : Scopes_In_Files_Map.Map;
    begin
       for Cur in Scopes.Iterate loop
          declare
-            Ref        : constant Scopes_In_Files_Map.Reference_Type :=
-              Scopes.Reference (Cur);
-            File_Scope : Scope_Entity renames
-              Scope_Entities_Trees.Element (Ref.File_Scope_Entity);
+            File_Scope        : File_Scope_Type :=
+              Scopes_In_Files_Map.Element (Cur);
+            File_Scope_Entity : Scope_Entity renames
+              Scope_Entities_Trees.Element (File_Scope.File_Scope_Entity);
          begin
-            --  If the file scope is empty, remove it
+            --  If the file scope is empty, do not add it to the resulting map
 
-            if File_Scope.To < File_Scope.From then
-               Ref.Scope_Entities.Delete_Subtree (Ref.File_Scope_Entity);
-            else
-               Remap_Scope_Entities (Ref.Scope_Entities, SCO_Map);
+            if File_Scope_Entity.To >= File_Scope_Entity.From then
+               Remap_Scope_Entities (File_Scope.Scope_Entities, SCO_Map);
+               Res.Insert (Scopes_In_Files_Map.Key (Cur), File_Scope);
             end if;
          end;
       end loop;
+      Scopes := Res;
    end Remap_Scopes;
 
    ----------------