improve git describe

library/CMakeLists.txt

@@ -353,19 +353,52 @@ if(DFHACK_PRERELEASE)
 endif()
 
 configure_file(git-describe.cmake.in ${CMAKE_CURRENT_SOURCE_DIR}/git-describe.cmake @ONLY)
-if(EXISTS ${dfhack_SOURCE_DIR}/.git/index AND EXISTS ${dfhack_SOURCE_DIR}/.git/modules/library/xml/index)
-    add_custom_command(OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/include/git-describe.h
-    COMMAND ${CMAKE_COMMAND}
-        -D dfhack_SOURCE_DIR:STRING=${dfhack_SOURCE_DIR}
-        -D GIT_EXECUTABLE:STRING=${GIT_EXECUTABLE}
-        -P ${CMAKE_CURRENT_SOURCE_DIR}/git-describe.cmake
-    COMMENT "Obtaining git commit information"
-    DEPENDS ${dfhack_SOURCE_DIR}/.git/index
-        ${dfhack_SOURCE_DIR}/.git/modules/library/xml/index
-        ${CMAKE_CURRENT_SOURCE_DIR}/git-describe.cmake
-        include/git-describe.h.in
-    )
-endif()
+
+# .git is a directory in a normal repository, but a file containing
+# "gitdir: <path>" in git worktrees and submodules; resolve both.
+function(dfhack_find_git_dir repo_dir out_var)
+    set(${out_var} "" PARENT_SCOPE)
+    if(IS_DIRECTORY "${repo_dir}/.git")
+        set(${out_var} "${repo_dir}/.git" PARENT_SCOPE)
+    elseif(EXISTS "${repo_dir}/.git")
+        file(STRINGS "${repo_dir}/.git" gitdir_line REGEX "^gitdir:" LIMIT_COUNT 1)
+        if(gitdir_line MATCHES "^gitdir:[ \t]*(.+)")
+            string(STRIP "${CMAKE_MATCH_1}" gitdir)
+            if(NOT IS_ABSOLUTE "${gitdir}")
+                get_filename_component(gitdir "${repo_dir}/${gitdir}" ABSOLUTE)
+            endif()
+            set(${out_var} "${gitdir}" PARENT_SCOPE)
+        endif()
+    endif()
+endfunction()
+
+# Re-run git describe when HEAD or the index changes in the main repository or
+# in the library/xml submodule, when they are present. The header is generated
+# even outside a git checkout so the build works on plain source trees too.
+set(GIT_DESCRIBE_DEPS
+    ${CMAKE_CURRENT_SOURCE_DIR}/git-describe.cmake
+    ${CMAKE_CURRENT_SOURCE_DIR}/include/git-describe.h.in
+)
+dfhack_find_git_dir("${dfhack_SOURCE_DIR}" DFHACK_GIT_DIR)
+dfhack_find_git_dir("${dfhack_SOURCE_DIR}/library/xml" DFHACK_XML_GIT_DIR)
+foreach(git_dir "${DFHACK_GIT_DIR}" "${DFHACK_XML_GIT_DIR}")
+    if(git_dir)
+        foreach(name HEAD index)
+            if(EXISTS "${git_dir}/${name}")
+                list(APPEND GIT_DESCRIBE_DEPS "${git_dir}/${name}")
+            endif()
+        endforeach()
+    endif()
+endforeach()
+
+add_custom_command(OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/include/git-describe.h
+COMMAND ${CMAKE_COMMAND}
+    -D dfhack_SOURCE_DIR:STRING=${dfhack_SOURCE_DIR}
+    -D GIT_EXECUTABLE:STRING=${GIT_EXECUTABLE}
+    -P ${CMAKE_CURRENT_SOURCE_DIR}/git-describe.cmake
+COMMENT "Obtaining git commit information"
+DEPENDS ${GIT_DESCRIBE_DEPS}
+)
 
 add_library(dfhack SHARED ${PROJECT_SOURCES})
 target_compile_definitions(dfhack PRIVATE BUILD_DFHACK_LIB)

library/git-describe.cmake.in

@@ -1,48 +1,61 @@
 # Generated from git-describe.cmake.in
 set(DFHACK_BUILD_ID "@DFHACK_BUILD_ID@")
 
-if(NOT(EXISTS "${GIT_EXECUTABLE}"))
-    message(FATAL_ERROR "git-describe failed: could not find git at ${GIT_EXECUTABLE}")
-endif()
+# Fallbacks used when the source tree is not a git checkout or when revision
+# information cannot be obtained.
+set(DFHACK_GIT_DESCRIPTION "@DFHACK_VERSION@-unknown")
+set(DFHACK_GIT_COMMIT "unknown")
+set(DFHACK_GIT_XML_EXPECTED_COMMIT "unknown")
+set(DFHACK_GIT_XML_COMMIT "unknown")
+set(DFHACK_GIT_TAGGED FALSE)
+set(DFHACK_GIT_XML_MATCH FALSE)
 
-execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --abbrev=8 --long
-    WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
-    OUTPUT_VARIABLE DFHACK_GIT_DESCRIPTION
-    OUTPUT_STRIP_TRAILING_WHITESPACE
-    RESULT_VARIABLE DFHACK_GIT_DESCRIPTION_RESULT)
-execute_process(COMMAND ${GIT_EXECUTABLE} rev-parse HEAD
-    WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
-    OUTPUT_VARIABLE DFHACK_GIT_COMMIT
-    OUTPUT_STRIP_TRAILING_WHITESPACE)
-execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --abbrev=8 --exact-match
-    WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
-    RESULT_VARIABLE DFHACK_GIT_TAGGED_RESULT
-    OUTPUT_QUIET ERROR_QUIET)
+if(EXISTS "${dfhack_SOURCE_DIR}/.git")
+    if(NOT GIT_EXECUTABLE OR NOT EXISTS "${GIT_EXECUTABLE}")
+        message(WARNING "git-describe: could not find git; version information will be unavailable")
+    else()
+        execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --abbrev=8 --long
+            WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
+            OUTPUT_VARIABLE DFHACK_GIT_DESCRIPTION
+            OUTPUT_STRIP_TRAILING_WHITESPACE
+            RESULT_VARIABLE DFHACK_GIT_DESCRIPTION_RESULT)
+        execute_process(COMMAND ${GIT_EXECUTABLE} rev-parse HEAD
+            WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
+            OUTPUT_VARIABLE DFHACK_GIT_COMMIT
+            OUTPUT_STRIP_TRAILING_WHITESPACE)
+        execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --abbrev=8 --exact-match
+            WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
+            RESULT_VARIABLE DFHACK_GIT_TAGGED_RESULT
+            OUTPUT_QUIET ERROR_QUIET)
 
-# Check library/xml for matching commits
-execute_process(COMMAND ${GIT_EXECUTABLE} rev-parse HEAD:library/xml
-    WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
-    OUTPUT_VARIABLE DFHACK_GIT_XML_EXPECTED_COMMIT
-    OUTPUT_STRIP_TRAILING_WHITESPACE)
-execute_process(COMMAND ${GIT_EXECUTABLE} rev-parse HEAD
-    WORKING_DIRECTORY "${dfhack_SOURCE_DIR}/library/xml"
-    OUTPUT_VARIABLE DFHACK_GIT_XML_COMMIT
-    OUTPUT_STRIP_TRAILING_WHITESPACE)
+        # Check library/xml for matching commits
+        execute_process(COMMAND ${GIT_EXECUTABLE} rev-parse HEAD:library/xml
+            WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
+            OUTPUT_VARIABLE DFHACK_GIT_XML_EXPECTED_COMMIT
+            OUTPUT_STRIP_TRAILING_WHITESPACE)
+        if(EXISTS "${dfhack_SOURCE_DIR}/library/xml/.git")
+            execute_process(COMMAND ${GIT_EXECUTABLE} rev-parse HEAD
+                WORKING_DIRECTORY "${dfhack_SOURCE_DIR}/library/xml"
+                OUTPUT_VARIABLE DFHACK_GIT_XML_COMMIT
+                OUTPUT_STRIP_TRAILING_WHITESPACE)
+        endif()
 
-if(NOT(${DFHACK_GIT_DESCRIPTION_RESULT} EQUAL 0))
-    message(FATAL_ERROR "git-describe failed: ${DFHACK_GIT_DESCRIPTION_RESULT}")
-endif()
+        if(DFHACK_GIT_TAGGED_RESULT STREQUAL "0")
+            set(DFHACK_GIT_TAGGED TRUE)
+        endif()
 
-if(${DFHACK_GIT_TAGGED_RESULT} EQUAL 0)
-    set(DFHACK_GIT_TAGGED TRUE)
-else()
-    set(DFHACK_GIT_TAGGED FALSE)
-endif()
+        if(NOT "${DFHACK_GIT_XML_COMMIT}" STREQUAL ""
+                AND NOT "${DFHACK_GIT_XML_COMMIT}" STREQUAL "unknown"
+                AND "${DFHACK_GIT_XML_COMMIT}" STREQUAL "${DFHACK_GIT_XML_EXPECTED_COMMIT}")
+            set(DFHACK_GIT_XML_MATCH TRUE)
+        endif()
 
-if(${DFHACK_GIT_XML_COMMIT} STREQUAL ${DFHACK_GIT_XML_EXPECTED_COMMIT})
-    set(DFHACK_GIT_XML_MATCH TRUE)
-else()
-    set(DFHACK_GIT_XML_MATCH FALSE)
+        if(NOT DFHACK_GIT_DESCRIPTION_RESULT STREQUAL "0")
+            # e.g. a clone with no reachable tags; fall back to the commit hash
+            message(WARNING "git-describe: 'git describe' failed; using commit hash as description")
+            set(DFHACK_GIT_DESCRIPTION "${DFHACK_GIT_COMMIT}")
+        endif()
+    endif()
 endif()
 
 configure_file(${dfhack_SOURCE_DIR}/library/include/git-describe.h.in ${dfhack_SOURCE_DIR}/library/include/git-describe.h)

library/include/git-describe.h.in

@@ -1,7 +1,7 @@
-#cmakedefine DFHACK_GIT_DESCRIPTION "@DFHACK_GIT_DESCRIPTION@"
-#cmakedefine DFHACK_GIT_COMMIT "@DFHACK_GIT_COMMIT@"
-#cmakedefine DFHACK_GIT_XML_EXPECTED_COMMIT "@DFHACK_GIT_XML_EXPECTED_COMMIT@"
-#cmakedefine DFHACK_GIT_XML_COMMIT "@DFHACK_GIT_XML_COMMIT@"
+#define DFHACK_GIT_DESCRIPTION "@DFHACK_GIT_DESCRIPTION@"
+#define DFHACK_GIT_COMMIT "@DFHACK_GIT_COMMIT@"
+#define DFHACK_GIT_XML_EXPECTED_COMMIT "@DFHACK_GIT_XML_EXPECTED_COMMIT@"
+#define DFHACK_GIT_XML_COMMIT "@DFHACK_GIT_XML_COMMIT@"
 #define DFHACK_BUILD_ID "@DFHACK_BUILD_ID@"
 #cmakedefine DFHACK_GIT_TAGGED
 #cmakedefine DFHACK_GIT_XML_MATCH