factor out config.sh script to update config files (VERSION, SYSCONFDIR)

- use generated/dub as string import path for copied/generated config files

config.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+
+set -ue
+
+OUTDIR="$1"
+VERSIONFILE="$2"
+SYSCONFDIR="$3"
+VERSION=$(git describe --dirty 2>/dev/null || cat "$VERSIONFILE") # prefer git describe
+
+mkdir -p "$OUTDIR"
+# only update config files when they actually differ to avoid unnecessary rebuilds
+if [ "$VERSION" != "$(cat "$OUTDIR/VERSION" 2>/dev/null)" ]; then
+    printf "$VERSION" > "$OUTDIR/VERSION"
+fi
+if [ "$SYSCONFDIR" != "$(cat "$OUTDIR/SYSCONFDIR.imp" 2>/dev/null)" ]; then
+    printf "$SYSCONFDIR" > "$OUTDIR/SYSCONFDIR.imp"
+fi

dub.sdl

@@ -29,9 +29,8 @@ subPackage {
     "src/ddmd/tokens.d" \
     "src/ddmd/utf.d"
 
-  // stringImportPaths cannot be used because it will make Dub extremely slow
-  // https://github.com/dlang/dub/issues/1199
-  dflags "-J$PACKAGE_DIR"
+  preGenerateCommands `cd "$${DUB_PACKAGE_DIR}" && ./config.sh generated/dub VERSION /etc`
+  stringImportPaths "generated/dub"
 
   dependency "dmd:root" version="*"
 }

src/posix.mak

@@ -459,17 +459,7 @@ optabgen.out : $G/optabgen
 
 ######## VERSION
 
-VERSION := $(shell cat ../VERSION) # default to checked-in VERSION file
-ifneq (1,$(RELEASE)) # unless building a release
-	VERSION := $(shell printf "`$(GIT) describe --dirty || cat ../VERSION`") # use git describe
-endif
-
-# only update $G/VERSION when it differs to avoid unnecessary rebuilds
-$(shell test $(VERSION) != "`cat $G/VERSION 2> /dev/null`" \
-		&& printf $(VERSION) > $G/VERSION )
-
-$(shell test $(SYSCONFDIR) != "`cat $G/SYSCONFDIR.imp 2> /dev/null`" \
-		&& printf '$(SYSCONFDIR)' > $G/SYSCONFDIR.imp )
+$(shell ../config.sh "$G" ../VERSION $(SYSCONFDIR))
 
 #########
 # Specific dependencies other than the source file for all objects