build: use a link instead of changing current directory when compiling

If links don't work, fall back to using the full source path as was
previously done.

This should fix build failures with MSVC.

Reviewed-by: Hendrik Leppkes <h.leppkes@gmail.com>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

.gitignore

@@ -64,6 +64,7 @@
 /libavcodec/*_tables.h
 /libavutil/avconfig.h
 /libavutil/ffversion.h
+/src
 /tests/audiogen
 /tests/base64
 /tests/checkasm/checkasm

Makefile

@@ -181,7 +181,7 @@ clean::
 
 distclean::
 	$(RM) $(DISTCLEANSUFFIXES)
-	$(RM) config.* .config libavutil/avconfig.h .version avversion.h version.h libavutil/ffversion.h libavcodec/codec_names.h
+	$(RM) config.* .config libavutil/avconfig.h .version avversion.h version.h libavutil/ffversion.h libavcodec/codec_names.h src
 	$(RM) -rf doc/examples/pc-uninstalled
 
 config:

common.mak

@@ -32,7 +32,7 @@ endif
 ALLFFLIBS = avcodec avdevice avfilter avformat avresample avutil postproc swscale swresample
 
 # NASM requires -I path terminated with /
-IFLAGS     := -I$(DST_PATH)/ -I$(SRC_PATH)/
+IFLAGS     := -I. -I$(SRC_LINK)/
 CPPFLAGS   := $(IFLAGS) $(CPPFLAGS)
 CFLAGS     += $(ECFLAGS)
 CCFLAGS     = $(CPPFLAGS) $(CFLAGS)
@@ -43,12 +43,11 @@ CXXFLAGS   += $(CPPFLAGS) $(CFLAGS)
 YASMFLAGS  += $(IFLAGS:%=%/) -Pconfig.asm
 
 HOSTCCFLAGS = $(IFLAGS) $(HOSTCPPFLAGS) $(HOSTCFLAGS)
-LDFLAGS    := $(ALLFFLIBS:%=$(LD_PATH)$(DST_PATH)/lib%) $(LDFLAGS)
+LDFLAGS    := $(ALLFFLIBS:%=$(LD_PATH)lib%) $(LDFLAGS)
 
 define COMPILE
        $(call $(1)DEP,$(1))
-       $(Q)cd $(SRC_PATH); if [ -n "$(findstring $(SRC_PATH),$<)" ]; then dest=$(subst $(SRC_PATH)/,,$<); else dest=$(DST_PATH)/$<; fi; \
-       $(subst @,,$($(1))) $($(1)FLAGS) $($(1)_DEPFLAGS:$(@:.o=.d)=$(DST_PATH)/$(@:.o=.d)) $($(1)_C) $($(1)_O:$@=$(DST_PATH)/$@) $$dest
+       $($(1)) $($(1)FLAGS) $($(1)_DEPFLAGS) $($(1)_C) $($(1)_O) $(patsubst $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
 endef
 
 COMPILE_C = $(call COMPILE,CC)

configure

@@ -4696,6 +4696,26 @@ case $target_os in
         ;;
 esac
 
+# test if creating links works
+link_dest=$(mktemp -u $TMPDIR/dest_XXXXXXXX)
+link_name=$(mktemp -u $TMPDIR/name_XXXXXXXX)
+mkdir "$link_dest"
+$ln_s "$link_dest" "$link_name"
+touch "$link_dest/test_file"
+if [ -e "$link_name/test_file" ]; then
+    # create link to source path
+    [ -e src ] && rm src
+    $ln_s "$source_path" src
+    source_link=src
+else
+    # creating directory links doesn't work
+    # fall back to using the full source path
+    source_link="$source_path"
+fi
+# cleanup
+rm -r "$link_dest"
+rm -r "$link_name"
+
 # determine libc flavour
 
 probe_libc(){
@@ -6229,12 +6249,6 @@ enabled stripping || strip="echo skipping strip"
 
 config_files="$TMPH config.mak doc/config.texi"
 
-if enabled msvc; then
-    dst_path=$(pwd -W)
-else
-    dst_path=$(pwd)
-fi
-
 cat > config.mak <<EOF
 # Automatically generated by configure - do not modify!
 ifndef FFMPEG_CONFIG_MAK
@@ -6250,10 +6264,10 @@ DOCDIR=\$(DESTDIR)$docdir
 MANDIR=\$(DESTDIR)$mandir
 PKGCONFIGDIR=\$(DESTDIR)$pkgconfigdir
 SRC_PATH=$source_path
+SRC_LINK=$source_link
 ifndef MAIN_MAKEFILE
 SRC_PATH:=\$(SRC_PATH:.%=..%)
 endif
-DST_PATH=$dst_path
 CC_IDENT=$cc_ident
 ARCH=$arch
 INTRINSICS=$intrinsics

library.mak

@@ -28,7 +28,7 @@ $(SUBDIR)x86/%$(DEFAULT_YASMD).asm: $(SUBDIR)x86/%.asm
 
 $(SUBDIR)x86/%.o: $(SUBDIR)x86/%$(YASMD).asm
 	$(DEPYASM) $(YASMFLAGS) -I $(<D)/ -M -o $@ $< > $(@:.o=.d)
-	$(Q)cd $(SRC_PATH); $(subst @,,$(YASM)) $(YASMFLAGS) -I $(<D)/ -o $(DST_PATH)/$@ $(subst $(SRC_PATH)/,,$<)
+	$(YASM) $(YASMFLAGS) -I $(<D)/ -o $@ $(patsubst $(SRC_PATH)/%,$(SRC_LINK)/%,$<)
 	-$(if $(ASMSTRIPFLAGS), $(STRIP) $(ASMSTRIPFLAGS) $@)
 
 LIBOBJS := $(OBJS) $(SUBDIR)%.h.o $(TESTOBJS)