Generate an empty buffers unit list that is -pedantic compliant

Author: Jugst3r

testsuite/tests/integrated_instrumentation/no_uoi/Makefile

@@ -0,0 +1,11 @@
+CC=g++
+OBJ = pkg.o test.o
+
+%.o: %.c
+	$(CC) -c -pedantic -Wall -o $@ $<
+
+test: $(OBJ)
+	$(CC) -pedantic -o $@ $^
+
+clean:
+	rm -f *.o test

testsuite/tests/integrated_instrumentation/no_uoi/pkg.c

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

testsuite/tests/integrated_instrumentation/no_uoi/test.c

@@ -0,0 +1,8 @@
+extern int foo ();
+
+int
+main ()
+{
+  foo ();
+  return 0;
+}

testsuite/tests/integrated_instrumentation/no_uoi/test.py

@@ -0,0 +1,42 @@
+"""
+Check that gnatcov does not break compilation with the -pedantic switch. The
+code generated for an empty buffers list used to be uncompilable with
+-pedantic. Note that -pedantic should only diagnose warnings and not errors,
+so this is not expected, but we can work around the issue easily so fix the
+wrong code.
+"""
+
+import os
+import os.path
+
+from e3.fs import cp
+
+from SUITE.control import env
+from SUITE.cutils import Wdir
+from SCOV.minicheck import check_xcov_reports
+from SUITE.tutils import cmdrun, srctracename_for, thistest, xcov
+
+Wdir("tmp_")
+
+cwd = os.getcwd()
+
+# Then, setup the instrumentation process
+xcov(
+    [
+        "setup-integration",
+        "--level=stmt",
+        "--compilers=g++",
+        f"--output-dir={cwd}",
+    ]
+)
+
+# Shadow the compiler driver with the generated wrapper
+env.add_search_path(env_var="PATH", path=cwd)
+
+# Then, run the build process unchanged
+cmdrun(["make", "-C", "..", "test"], for_pgm=False)
+
+# Run the executable
+cmdrun(["../test"], for_pgm=False)
+
+thistest.result()

tools/gnatcov/instrument-c.adb

@@ -4413,15 +4413,24 @@ package body Instrument.C is
       CU_File.Put_Line (Self.Extern_Prefix & Buffer_Array_Decl & ";");
       CU_File.Put_Line (Buffer_Array_Decl & " = {");
       CU_File.Put_Line ("  " & Buffer_Unit_Length & ",");
-      CU_File.Put_Line
-        ("  (const struct gnatcov_rts_coverage_buffers_group *[]) {");
-      for BS of Buffer_Symbols loop
-         CU_File.Put ("    &" & (+BS));
-         if BS /= Buffer_Symbols.Last_Element then
-            CU_File.Put_Line (",");
-         end if;
-      end loop;
-      CU_File.Put_Line ("}};");
+      if String_Sets.Length (Buffer_Symbols) = 0 then
+
+         --  If there are no units of interest, create a NULL pointer to avoid
+         --  having an empty array.
+
+         CU_File.Put_Line ("NULL");
+      else
+         CU_File.Put_Line
+           ("  (const struct gnatcov_rts_coverage_buffers_group *[]) {");
+         for BS of Buffer_Symbols loop
+            CU_File.Put ("    &" & (+BS));
+            if BS /= Buffer_Symbols.Last_Element then
+               CU_File.Put_Line (",");
+            end if;
+         end loop;
+         CU_File.Put_Line ("}");
+      end if;
+      CU_File.Put_Line ("};");
       return CU_Name;
    end Emit_Buffers_List_Unit;