Updates to provide:

(1) major must match
(2) minor version backward compatibility check

     if minor versions don't match
         2a, check if either version is in the incompatible list (e.g., develop)
             print incompatibility warning and HDF5_DISABLE_VERSION_CHECK options
             abort if version check not disabled
         2b, check if header minor version is newer than library version
             print forward compatibility warning and HDF5_DISABLE_VERSION_CHECK options
             abort if version check not disabled
(3) release (patch) versionnot checked
(4) VERS_MINOR_EXCEPTIONS list now set to '999', and minor version '999' checked in
    test/tcheck_version.c.  This check will always cause the -tm option to fail and
    can remain in release branches, eliminating need to change or remove WILL_FAIL true
    for release branches.

Author: lrknox

src/H5.c

@@ -72,8 +72,13 @@ bool H5_PKG_INIT_VAR = false;
 /* Library Private Variables */
 /*****************************/
 
-/* Library incompatible minor versions, develop releases are incompatible by design */
-static const unsigned VERS_MINOR_EXCEPTIONS[]    = {0};
+/* Library known incompatible minor versions; develop releases are incompatible
+ * by design. 999 is entered for testing an exception as a minor version that 
+ * will never occur.  Any released minor version found to be truly incompatible
+ * (this should never happen) should be added to the list with 999.  999 alone
+ * in the list indicates that there are no incompatible minor versions. */
+static const unsigned VERS_MINOR_EXCEPTIONS[]    = {999};
+/* The size should be set to the number of minor version exceptions in the list. */
 static const unsigned VERS_MINOR_EXCEPTIONS_SIZE = 1;
 
 /* Library init / term status (global) */
@@ -832,6 +837,15 @@ H5get_libversion(unsigned *majnum /*out*/, unsigned *minnum /*out*/, unsigned *r
     "linked with an incompatible version of static or shared HDF5 library.\n"                                \
     "You should recompile the application or check your shared library related\n"                            \
     "settings such as 'LD_LIBRARY_PATH'.\n"
+#define MINOR_VERSION_FORWARD_COMPATIBLE_WARNING                                                             \
+    "Warning! ***HDF5 library minor version forward compatibility error***\n"                                \
+    "The HDF5 header files used to compile this application are from a newer\n"                              \
+    "version of the HDF5 library than the one to which this application is linked.\n"                        \
+    "Data corruption or segmentation faults may occur if the application continues.\n"                       \
+    "This can happen when an application was compiled by a newer version of HDF5 but\n"                      \
+    "linked with an older version of static or shared HDF5 library.\n"                                       \
+    "You should recompile the application or check your shared library related\n"                            \
+    "settings such as 'LD_LIBRARY_PATH'.\n"
 
 static herr_t
 H5_check_version(unsigned majnum, unsigned minnum, unsigned relnum)
@@ -842,6 +856,7 @@ H5_check_version(unsigned majnum, unsigned minnum, unsigned relnum)
     static unsigned int disable_version_check    = 0;     /* Set if the version check should be disabled */
     static const char  *version_mismatch_warning = VERSION_MISMATCH_WARNING;
     static const char  *minor_version_mismatch_warning = MINOR_VERSION_MISMATCH_WARNING;
+    static const char  *minor_version_forward_compatible_warning = MINOR_VERSION_FORWARD_COMPATIBLE_WARNING;
     herr_t              ret_value                      = SUCCEED; /* Return value */
 
     FUNC_ENTER_NOAPI_NOINIT_NOERR
@@ -938,6 +953,40 @@ H5_check_version(unsigned majnum, unsigned minnum, unsigned relnum)
 
         } /* end for */
 
+        /* Check for forward compatibilty usage. */
+        if (H5_VERS_MINOR > minnum) {
+            switch (disable_version_check) {
+                case 0:
+                    fprintf(stderr, "%s%s", minor_version_forward_compatible_warning,
+                            "You can, at your own risk, disable this warning by setting the environment\n"
+                            "variable 'HDF5_DISABLE_VERSION_CHECK' to a value of '1'.\n"
+                            "Setting it to 2 or higher will suppress the warning messages totally.\n");
+                    /* Mention the versions we are referring to */
+                    fprintf(stderr, "Headers are %u.%u.%u, library is %u.%u.%u\n", majnum, minnum, relnum,
+                            (unsigned)H5_VERS_MAJOR, (unsigned)H5_VERS_MINOR, (unsigned)H5_VERS_RELEASE);
+
+                    /* Bail out now. */
+                    fputs("Bye...\n", stderr);
+                    abort();
+                case 1:
+                    /* continue with a warning */
+                    /* Note that the warning message is embedded in the format string.*/
+                    fprintf(stderr,
+                            "%s'HDF5_DISABLE_VERSION_CHECK' "
+                            "environment variable is set to %d, application will\n"
+                            "continue at your own risk.\n",
+                            minor_version_forward_compatible_warning, disable_version_check);
+                    /* Mention the versions we are referring to */
+                    fprintf(stderr, "Headers are %u.%u.%u, library is %u.%u.%u\n", majnum, minnum, relnum,
+                            (unsigned)H5_VERS_MAJOR, (unsigned)H5_VERS_MINOR, (unsigned)H5_VERS_RELEASE);
+                    break;
+                default:
+                    /* 2 or higher: continue silently */
+                    break;
+            } /* end switch */
+
+        }
+
     } /* end if (H5_VERS_MINOR != minnum) */
 
     /* Indicate that the version check has been performed */

test/CMakeTests.cmake

@@ -654,7 +654,8 @@ set_tests_properties (H5TEST-tcheck_version-major PROPERTIES
 if ("H5TEST-tcheck_version-major" MATCHES "${HDF5_DISABLE_TESTS_REGEX}")
   set_tests_properties (H5TEST-tcheck_version-major PROPERTIES DISABLED true)
 endif ()
-# minor + 1 should pass on non-develop branches
+# The minor version test will test version 999 and always fail because it's listed in
+# VERS_MINOR_EXCEPTIONS.  With WILL_FAIL "true" the failing test passes.
 add_test (NAME H5TEST-tcheck_version-minor COMMAND $<TARGET_FILE:tcheck_version> "-tm")
 set_tests_properties (H5TEST-tcheck_version-minor PROPERTIES
     WORKING_DIRECTORY ${HDF5_TEST_BINARY_DIR}/H5TEST
@@ -664,11 +665,12 @@ set_tests_properties (H5TEST-tcheck_version-minor PROPERTIES
 if ("H5TEST-tcheck_version-minor" MATCHES "${HDF5_DISABLE_TESTS_REGEX}")
   set_tests_properties (H5TEST-tcheck_version-minor PROPERTIES DISABLED true)
 endif ()
+# release + 1 should always pass (not checked)
 add_test (NAME H5TEST-tcheck_version-release COMMAND $<TARGET_FILE:tcheck_version> "-tr")
 set_tests_properties (H5TEST-tcheck_version-release PROPERTIES
     WORKING_DIRECTORY ${HDF5_TEST_BINARY_DIR}/H5TEST
     ENVIRONMENT "${CROSSCOMPILING_PATH}"
-)
+) 
 if ("H5TEST-tcheck_version-release" MATCHES "${HDF5_DISABLE_TESTS_REGEX}")
   set_tests_properties (H5TEST-tcheck_version-release PROPERTIES DISABLED true)
 endif ()

test/tcheck_version.c

@@ -70,7 +70,7 @@ parse(int ac, char **av)
                             major++;
                             break;
                         case 'm':
-                            minor++;
+                            minor = 999;
                             break;
                         case 'r':
                             release++;