From 5961d6dc3724e2cf882ab07afbb9bbbfaeb4fd31 Mon Sep 17 00:00:00 2001
From: Ward Fisher <wfisher@ucar.edu>
Date: Tue, 26 May 2020 14:46:23 -0600
Subject: [PATCH 1/2] Added a check for m4 and throw an error if m4 isn't on
 the path and the generated file isn't present (as it would be in a point
 release). In support of https://github.com/Unidata/netcdf-c/issues/1739

---
 CMakeLists.txt | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index cb06a077f..2e9b7cc09 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1492,20 +1492,27 @@ ENDIF()
 
 MACRO(GEN_m4 filename)
 
+  # If m4 isn't present, and the generated file doesn't exist,
+  # it cannot be generated and an error should be thrown.
+  IF(NOT HAVE_M4)
+    IF(NOT EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${filename.c})
+      MESSAGE(FATAL_ERROR "m4 is required to generate ${filename}.c. Please install m4 so that it is on the PATH and try again.")
+    ENDIF()
+  ENDIF(NOT HAVE_M4)
+
   IF(HAVE_M4)
+    # If m4 is available, remove generated file if it exists.
+    IF(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c)
+      FILE(REMOVE ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c)
+    ENDIF()
 
-  # If m4 is available, remove generated file if it exists.
-  IF(EXISTS ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c)
-    FILE(REMOVE ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c)
-  ENDIF()
-
-  ADD_CUSTOM_COMMAND(
-    OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c
-    COMMAND ${NC_M4}
-    ARGS ${M4FLAGS} ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.m4 > ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c
-    VERBATIM
-    )
-ENDIF(HAVE_M4)
+    ADD_CUSTOM_COMMAND(
+      OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c
+      COMMAND ${NC_M4}
+      ARGS ${M4FLAGS} ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.m4 > ${CMAKE_CURRENT_SOURCE_DIR}/${filename}.c
+      VERBATIM
+      )
+  ENDIF(HAVE_M4)
 ENDMACRO(GEN_m4)
 
 # Binary tests, but ones which depend on value of 'TEMP_LARGE' being defined.

From 31712192b215eaaeda049eda843c1c8fc4b3176c Mon Sep 17 00:00:00 2001
From: Ward Fisher <wfisher@ucar.edu>
Date: Tue, 26 May 2020 16:09:10 -0600
Subject: [PATCH 2/2] More m4 fenceposting.

---
 CMakeLists.txt        | 1 +
 libsrc/CMakeLists.txt | 5 +++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2e9b7cc09..713fd6c44 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1488,6 +1488,7 @@ IF(NC_M4)
   SET(HAVE_M4 TRUE)
 ELSE()
   MESSAGE(STATUS "m4 not found.")
+  SET(HAVE_M4 FALSE)
 ENDIF()
 
 MACRO(GEN_m4 filename)
diff --git a/libsrc/CMakeLists.txt b/libsrc/CMakeLists.txt
index 65a3f8745..e3e28793e 100644
--- a/libsrc/CMakeLists.txt
+++ b/libsrc/CMakeLists.txt
@@ -4,9 +4,10 @@
 # Process these files with m4.
 SET(m4_SOURCES attr ncx putget t_ncxx)
 foreach (f ${m4_SOURCES})
-  IF(HAVE_M4)
     GEN_m4(${f})
-  ENDIF()
+    IF(NOT EXISTS ${f}.c)
+      MESSAGE(FATAL_ERROR "m4 is required to generate ${f}.c. Please install m4 on the PATH and try again.")
+    ENDIF()
 endforeach(f)
 
 SET(libsrc_SOURCES v1hpg.c putget.c attr.c nc3dispatch.c