MDEV-20787: Script dgcov.pl does not workbb-10.2-MDEV-20787

- This patch is done after doing test on 00f9df29224ada9cdbb796c99f4
where difference was found between versions of gcov.
- This patch doesn't take gcov versions in account since is extracting
filename of a `.gcov` file, which is generated with `gcov -i
<source-file>.gcda` during `dgcov.pl --generate`.
- There is a check if file exists.
Reason for that is because some generated `gcov` files are outliers from above
rule (that a file generated in intermediate format(gcov) has the same source name).
Example 1: `aestables.cpp.gcda` is not generating `aestables.cpp.gcov`,
but only the files used in #include `modes.hpp.gcov  runtime.hpp.gcov`
Example 2: `my_sha256.cc.gcda` is generating `my_sha.ic.gcov`
- Make sure to test `MTR_BINDIR` which gets set during out-of-source
build and generate error when running `./mysql-test/mtr --gcov alias`
- During the testing:
  10.1 results are stored in
  - `<basedir>//mysql-test-gcov.msg` and errors in
  - `<basedir>//mysql-test-gcov.err`
  10.2 results should be stored in
  `./mysql-test/var/last_changes.dgcov`, but only empty results are
  obtained (tests `1st` and `alias`).

3 files changed, 10 insertions, 4 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4734c6f7d5f..d536027c88e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -256,7 +256,7 @@ SET(CMAKE_C_FLAGS_DEBUG "${CMAKE_C_FLAGS_DEBUG} -DENABLED_DEBUG_SYNC")
  
 OPTION(ENABLE_GCOV "Enable gcov (debug, Linux builds only)" OFF)
 IF (ENABLE_GCOV)
-  MY_CHECK_AND_SET_COMPILER_FLAG("-fprofile-arcs -ftest-coverage -lgcov" DEBUG)
+  MY_CHECK_AND_SET_COMPILER_FLAG("--coverage" DEBUG)
 ENDIF()
 
 MY_CHECK_AND_SET_COMPILER_FLAG(-ggdb3 DEBUG)
diff --git a/mysql-test/dgcov.pl b/mysql-test/dgcov.pl
index fbc5540e697..f2bbdad4d20 100755
--- a/mysql-test/dgcov.pl
+++ b/mysql-test/dgcov.pl
@@ -161,8 +161,14 @@ sub gcov_one_file {
     system($cmd)==0 or die "system($cmd): $? $!";
   }
 
-  # now, read the generated file
-  open FH, '<', "$_.gcov" or die "open(<$_.gcov): $!";
+  (my $filename = $_)=~ s/\.[^.]+$//; # remove extension
+  my $gcov_file_path= $File::Find::dir."/$filename.gcov";
+  if (! -f $gcov_file_path)
+  {
+    return;
+  }
+  open FH, '<', "$gcov_file_path" or die "open(<$gcov_file_path): $!";
+
   my $fname;
   while (<FH>) {
     chomp;
diff --git a/mysql-test/mysql-test-run.pl b/mysql-test/mysql-test-run.pl
index 178d65aca41..be51a79e0be 100755
--- a/mysql-test/mysql-test-run.pl
+++ b/mysql-test/mysql-test-run.pl
@@ -1791,7 +1791,7 @@ sub command_line_setup {
   # --------------------------------------------------------------------------
   # Gcov flag
   # --------------------------------------------------------------------------
-  if ( ($opt_gcov or $opt_gprof) and ! $source_dist )
+  if ( ($opt_gcov or $opt_gprof) and (! $source_dist or -d $ENV{MTR_BINDIR}))
   {
     mtr_error("Coverage test needs the source - please use source dist");
   }