When CMake fails to download a file, display the error message (#6511)

Summary:
This helps to diagnose errors in the CMake build where it tries to retrieve dependencies.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6511

Differential Revision: D20387392

Pulled By: pdillinger

fbshipit-source-id: 7028dfd62704bcc747f39ff864ea9c9bf51cd1be

java/CMakeLists.txt

@@ -327,8 +327,9 @@ if(NOT EXISTS ${JAVA_JUNIT_JAR})
   message("Downloading ${JAVA_JUNIT_JAR}")
   file(DOWNLOAD ${DEPS_URL}/junit-4.12.jar ${JAVA_TMP_JAR} STATUS downloadStatus)
   list(GET downloadStatus 0 error_code)
+  list(GET downloadStatus 1 error_message)
   if(NOT error_code EQUAL 0)
-    message(FATAL_ERROR "Failed downloading ${JAVA_JUNIT_JAR}")
+    message(FATAL_ERROR "Failed downloading ${JAVA_JUNIT_JAR}: ${error_message}")
   endif()
   file(RENAME ${JAVA_TMP_JAR} ${JAVA_JUNIT_JAR})
 endif()
@@ -336,8 +337,9 @@ if(NOT EXISTS ${JAVA_HAMCR_JAR})
   message("Downloading ${JAVA_HAMCR_JAR}")
   file(DOWNLOAD ${DEPS_URL}/hamcrest-core-1.3.jar ${JAVA_TMP_JAR} STATUS downloadStatus)
   list(GET downloadStatus 0 error_code)
+  list(GET downloadStatus 1 error_message)
   if(NOT error_code EQUAL 0)
-    message(FATAL_ERROR "Failed downloading ${JAVA_HAMCR_JAR}")
+    message(FATAL_ERROR "Failed downloading ${JAVA_HAMCR_JAR}: ${error_message}")
   endif()
   file(RENAME ${JAVA_TMP_JAR} ${JAVA_HAMCR_JAR})
 endif()
@@ -345,8 +347,9 @@ if(NOT EXISTS ${JAVA_MOCKITO_JAR})
   message("Downloading ${JAVA_MOCKITO_JAR}")
   file(DOWNLOAD ${DEPS_URL}/mockito-all-1.10.19.jar ${JAVA_TMP_JAR} STATUS downloadStatus)
   list(GET downloadStatus 0 error_code)
+  list(GET downloadStatus 1 error_message)
   if(NOT error_code EQUAL 0)
-    message(FATAL_ERROR "Failed downloading ${JAVA_MOCKITO_JAR}")
+    message(FATAL_ERROR "Failed downloading ${JAVA_MOCKITO_JAR}: ${error_message}")
   endif()
   file(RENAME ${JAVA_TMP_JAR} ${JAVA_MOCKITO_JAR})
 endif()
@@ -354,8 +357,9 @@ if(NOT EXISTS ${JAVA_CGLIB_JAR})
   message("Downloading ${JAVA_CGLIB_JAR}")
   file(DOWNLOAD ${DEPS_URL}/cglib-2.2.2.jar ${JAVA_TMP_JAR} STATUS downloadStatus)
   list(GET downloadStatus 0 error_code)
+  list(GET downloadStatus 1 error_message)
   if(NOT error_code EQUAL 0)
-    message(FATAL_ERROR "Failed downloading ${JAVA_CGLIB_JAR}")
+    message(FATAL_ERROR "Failed downloading ${JAVA_CGLIB_JAR}: ${error_message}")
   endif()
   file(RENAME ${JAVA_TMP_JAR} ${JAVA_CGLIB_JAR})
 endif()
@@ -363,8 +367,9 @@ if(NOT EXISTS ${JAVA_ASSERTJ_JAR})
   message("Downloading ${JAVA_ASSERTJ_JAR}")
   file(DOWNLOAD ${DEPS_URL}/assertj-core-1.7.1.jar ${JAVA_TMP_JAR} STATUS downloadStatus)
   list(GET downloadStatus 0 error_code)
+  list(GET downloadStatus 1 error_message)
   if(NOT error_code EQUAL 0)
-    message(FATAL_ERROR "Failed downloading ${JAVA_ASSERTJ_JAR}")
+    message(FATAL_ERROR "Failed downloading ${JAVA_ASSERTJ_JAR}: ${error_message}")
   endif()
   file(RENAME ${JAVA_TMP_JAR} ${JAVA_ASSERTJ_JAR})
 endif()