diff --git a/assert_writeln_magic.d b/assert_writeln_magic.d
index 6b2892323b..b770c113ff 100755
--- a/assert_writeln_magic.d
+++ b/assert_writeln_magic.d
@@ -47,10 +47,10 @@ class TestVisitor : ASTVisitor
 {
     import dparse.lexer : tok, Token;
 
-    this(string fileName)
+    this(string fileName, string destFile)
     {
         this.fileName = fileName;
-        fl = FileLines(fileName);
+        fl = FileLines(fileName, destFile);
     }
 
     alias visit = ASTVisitor.visit;
@@ -176,7 +176,7 @@ private:
     FileLines fl;
 }
 
-void parseFile(string fileName)
+void parseFile(string fileName, string destFile)
 {
     import dparse.lexer;
     import dparse.parser : parseModule;
@@ -195,22 +195,31 @@ void parseFile(string fileName)
 
     RollbackAllocator rba;
     auto m = parseModule(tokens, fileName, &rba);
-    auto visitor = new TestVisitor(fileName);
+    auto visitor = new TestVisitor(fileName, destFile);
     visitor.visit(m);
     delete visitor;
 }
 
+// Modify a path under oldBase to a new path with the same subpath under newBase.
+// E.g.: `/foo/bar`.rebasePath(`/foo`, `/quux`) == `/quux/bar`
+string rebasePath(string path, string oldBase, string newBase)
+{
+    import std.path : absolutePath, buildPath, relativePath;
+    return buildPath(newBase, path.absolutePath.relativePath(oldBase.absolutePath));
+}
+
 void main(string[] args)
 {
     import std.file;
     import std.getopt;
-    import std.path : asNormalizedPath;
+    import std.path;
 
-    string inputDir;
+    string inputDir, outputDir;
     string[] ignoredFiles;
 
     auto helpInfo = getopt(args, config.required,
             "inputdir|i", "Folder to start the recursive search for unittest blocks (can be a single file)", &inputDir,
+            "outputdir|o", "Alternative folder to use as output (can be a single file)", &outputDir,
             "ignore", "List of files to exclude (partial matching is supported)", &ignoredFiles);
 
     if (helpInfo.helpWanted)
@@ -224,10 +233,14 @@ Tries to lower EqualExpression in AssertExpressions of Unittest blocks to commen
 
     DirEntry[] files;
 
+    // inputDir as default output directory
+    if (!outputDir.length)
+        outputDir = inputDir;
+
     if (inputDir.isFile)
     {
         files = [DirEntry(inputDir)];
-        inputDir = ".";
+        inputDir = "";
     }
     else
     {
@@ -236,13 +249,21 @@ Tries to lower EqualExpression in AssertExpressions of Unittest blocks to commen
     }
 
     foreach (file; files)
+    {
         if (!ignoredFiles.any!(x => file.name.canFind(x)))
-            file.name.parseFile;
+        {
+            // single files
+            if (inputDir.length == 0)
+                parseFile(file.name, outputDir);
+            else
+                parseFile(file.name, file.name.rebasePath(inputDir, outputDir));
+        }
+    }
 }
 
 /**
 A simple line-based in-memory representation of a file.
- - will automatically write all changes when the objct is destructed
+ - will automatically write all changes when the object is destructed
  - will use a temporary file to do safe, whole file swaps
 */
 struct FileLines
@@ -250,58 +271,48 @@ struct FileLines
     import std.array, std.file, std.path;
 
     string[] lines;
-    string destFile, path, tmpDir;
+    string destFile;
+    bool overwriteInputFile;
     bool hasWrittenChanges;
 
-    this(string path)
-    {
-        this(path.dirName, path.baseName);
-    }
-
-    this(string repoDir, string path)
+    this(string inputFile, string destFile)
     {
-        writeln("opening: ", path);
-
-        this.path = path;
-        destFile = buildPath(repoDir, path);
-        lines = File(destFile).byLineCopy.array;
+        stderr.writefln("%s -> %s", inputFile, destFile);
+        this.overwriteInputFile = inputFile == destFile;
+        this.destFile = destFile;
+        lines = File(inputFile).byLineCopy.array;
 
-        // it's a good practise to use a common tmp folder -> easier to look at or clean
-        tmpDir = buildPath(tempDir, "file_tester", path.stripExtension.replace("/", "_"));
-        tmpDir.mkdirRecurse;
+        destFile.dirName.mkdirRecurse;
     }
 
     // dumps all changes
     ~this()
     {
-        if (!hasWrittenChanges)
-            return;
-
-        auto tmpFile = writeLinesToFile;
-        tmpFile.copy(destFile);
-        tmpFile.remove;
-        tmpDir.rmdirRecurse;
+        if (overwriteInputFile)
+        {
+            if (hasWrittenChanges)
+            {
+                auto tmpFile = File(destFile ~ ".tmp", "w");
+                writeLinesToFile(tmpFile);
+                tmpFile.close;
+                tmpFile.name.rename(destFile);
+            }
+        }
+        else
+        {
+            writeLinesToFile(File(destFile, "w"));
+        }
     }
 
     // writes all changes to a random, temporary file
-    auto writeLinesToFile(string s = null) {
-        import std.uuid;
-
-        if (!s.length)
-            s = buildPath(tmpDir, randomUUID.to!string.replace("-", "") ~ ".d");
-
-        writeln("writing: ", path);
-        auto outFile = File(s, "w");
+    void writeLinesToFile(File outFile) {
         // dump file
         foreach (line; lines)
             outFile.writeln(line);
         // within the docs we automatically inject std.stdio (hence we need to do the same here)
         // writeln needs to be @nogc, @safe, pure and nothrow (we just fake it)
-        if (hasWrittenChanges)
-            outFile.writeln("// \nprivate void writeln(T)(T l) { }");
-
+        outFile.writeln("// \nprivate void writeln(T)(T l) { }");
         outFile.flush;
-        return s;
     }
 
     string opIndex(size_t i) { return lines[i]; }
diff --git a/osmodel.mak b/osmodel.mak
new file mode 100644
index 0000000000..d0f160ae37
--- /dev/null
+++ b/osmodel.mak
@@ -0,0 +1,55 @@
+# This Makefile snippet detects the OS and the architecture MODEL
+# Keep this file in sync between druntime, phobos, and dmd repositories!
+
+ifeq (,$(OS))
+  uname_S:=$(shell uname -s)
+  ifeq (Darwin,$(uname_S))
+    OS:=osx
+  endif
+  ifeq (Linux,$(uname_S))
+    OS:=linux
+  endif
+  ifeq (FreeBSD,$(uname_S))
+    OS:=freebsd
+  endif
+  ifeq (NetBSD,$(uname_S))
+    OS:=netbsd
+  endif
+  ifeq (OpenBSD,$(uname_S))
+    OS:=openbsd
+  endif
+  ifeq (Solaris,$(uname_S))
+    OS:=solaris
+  endif
+  ifeq (SunOS,$(uname_S))
+    OS:=solaris
+  endif
+  ifeq (,$(OS))
+    $(error Unrecognized or unsupported OS for uname: $(uname_S))
+  endif
+endif
+
+# When running make from XCode it may set environment var OS=MACOS.
+# Adjust it here:
+ifeq (MACOS,$(OS))
+  OS:=osx
+endif
+
+ifeq (,$(MODEL))
+  ifeq ($(OS), solaris)
+    uname_M:=$(shell isainfo -n)
+  else
+    uname_M:=$(shell uname -m)
+  endif
+  ifneq (,$(findstring $(uname_M),x86_64 amd64))
+    MODEL:=64
+  endif
+  ifneq (,$(findstring $(uname_M),i386 i586 i686))
+    MODEL:=32
+  endif
+  ifeq (,$(MODEL))
+    $(error Cannot figure 32/64 model from uname -m: $(uname_M))
+  endif
+endif
+
+MODEL_FLAG:=-m$(MODEL)
diff --git a/posix.mak b/posix.mak
index 0fd817d652..05040d16ab 100644
--- a/posix.mak
+++ b/posix.mak
@@ -9,6 +9,8 @@
 # make -f posix.mak rsync
 #
 
+include osmodel.mak
+
 # Latest released version
 ifeq (,${LATEST})
 LATEST:=$(shell cat VERSION)
@@ -16,15 +18,19 @@ endif
 # Next major DMD release
 NEXT_VERSION:=$(shell bash -c 'version=$$(cat VERSION);a=($${version//./ });a[1]="10\#$${a[1]}";((a[1]++)); a[2]=0; echo $${a[0]}.0$${a[1]}.$${a[2]};' )
 
-# Externals
+# DLang directories
 DMD_DIR=../dmd
 PHOBOS_DIR=../phobos
 DRUNTIME_DIR=../druntime
 TOOLS_DIR=../tools
+INSTALLER_DIR=../installer
 DUB_DIR=../dub-${DUB_VER}
+
+# External binaries
 DMD=$(DMD_DIR)/src/dmd
-DMD_REL=$(DMD_DIR)-${LATEST}/src/dmd
 DUB=${DUB_DIR}/bin/dub
+
+# External directories
 DOC_OUTPUT_DIR:=$(shell pwd)/web
 GIT_HOME=https://github.com/dlang
 DPL_DOCS_PATH=dpl-docs
@@ -33,13 +39,24 @@ REMOTE_DIR=d-programming@digitalmars.com:data
 
 # Last released versions
 DMD_STABLE_DIR=${DMD_DIR}-${LATEST}
+DMD_REL=$(DMD_STABLE_DIR)/src/dmd
 DRUNTIME_STABLE_DIR=${DRUNTIME_DIR}-${LATEST}
 PHOBOS_STABLE_DIR=${PHOBOS_DIR}-${LATEST}
 
+################################################################################
 # Automatically generated directories
 GENERATED=.generated
 PHOBOS_DIR_GENERATED=$(GENERATED)/phobos-prerelease
 PHOBOS_STABLE_DIR_GENERATED=$(GENERATED)/phobos-release
+# The assert_writeln_magic tool transforms all source files from Phobos. Hence
+# - a temporary folder with a copy of Phobos needs to be generated
+# - a list of all files in Phobos and the temporary copy is needed to setup proper
+#   Makefile dependencies and rules
+PHOBOS_FILES := $(shell find $(PHOBOS_DIR) -name '*.d' -o -name '*.mak' -o -name '*.ddoc')
+PHOBOS_FILES_GENERATED := $(subst $(PHOBOS_DIR), $(PHOBOS_DIR_GENERATED), $(PHOBOS_FILES))
+PHOBOS_STABLE_FILES := $(shell find $(PHOBOS_STABLE_DIR) -name '*.d' -o -name '*.mak' -o -name '*.ddoc')
+PHOBOS_STABLE_FILES_GENERATED := $(subst $(PHOBOS_STABLE_DIR), $(PHOBOS_STABLE_DIR_GENERATED), $(PHOBOS_STABLE_FILES))
+################################################################################
 
 # stable dub and dmd versions used to build dpl-docs
 DUB_VER=1.1.0
@@ -74,47 +91,6 @@ CHANGE_SUFFIX = \
  for f in `find "$3" -iname '*.$1'`; do\
   mv $$f `dirname $$f`/`basename $$f .$1`.$2; done
 
-# Set to 1 in the command line to minify css files
-CSS_MINIFY=
-
-# OS and MODEL
-OS:=
-uname_S:=$(shell uname -s)
-ifeq (Darwin,$(uname_S))
-    OS:=osx
-endif
-ifeq (Linux,$(uname_S))
-    OS:=linux
-endif
-ifeq (FreeBSD,$(uname_S))
-    OS:=freebsd
-endif
-ifeq (OpenBSD,$(uname_S))
-    OS:=openbsd
-endif
-ifeq (Solaris,$(uname_S))
-    OS:=solaris
-endif
-ifeq (SunOS,$(uname_S))
-    OS:=solaris
-endif
-ifeq (,$(OS))
-    $(error Unrecognized or unsupported OS for uname: $(uname_S))
-endif
-
-ifeq (,$(MODEL))
-    uname_M:=$(shell uname -m)
-    ifneq (,$(findstring $(uname_M),x86_64 amd64))
-        MODEL:=64
-    endif
-    ifneq (,$(findstring $(uname_M),i386 i586 i686))
-        MODEL:=32
-    endif
-    ifeq (,$(MODEL))
-        $(error Cannot figure 32/64 model from uname -m: $(uname_M))
-    endif
-endif
-
 # Disable all dynamic content that could potentially have an unrelated impact
 # on a diff
 ifeq (1,$(DIFFABLE))
@@ -124,14 +100,12 @@ else
 	CHANGELOG_VERSION := "v${LATEST}..upstream/stable"
 endif
 
-# Documents
+################################################################################
+# Resources
+################################################################################
 
-DDOC=$(addsuffix .ddoc, macros html dlang.org doc ${GENERATED}/${LATEST}) $(NODATETIME)
-STD_DDOC=$(addsuffix .ddoc, macros html dlang.org ${GENERATED}/${LATEST} std std_navbar-release ${GENERATED}/modlist-${LATEST}) $(NODATETIME)
-STD_DDOC_PRE=$(addsuffix .ddoc, macros html dlang.org ${GENERATED}/${LATEST} std std_navbar-prerelease ${GENERATED}/modlist-prerelease) $(NODATETIME)
-SPEC_DDOC=${DDOC} spec/spec.ddoc
-CHANGELOG_DDOC=${DDOC} changelog/changelog.ddoc $(NODATETIME)
-CHANGELOG_PRE_DDOC=${CHANGELOG_DDOC} changelog/prerelease.ddoc
+# Set to 1 in the command line to minify css files
+CSS_MINIFY=
 
 ORGS_USING_D=$(wildcard images/orgs-using-d/*)
 IMAGES=favicon.ico $(ORGS_USING_D) $(addprefix images/, \
@@ -155,6 +129,17 @@ JAVASCRIPT=$(addsuffix .js, $(addprefix js/, \
 STYLES=$(addsuffix .css, $(addprefix css/, \
 	style print codemirror ddox))
 
+################################################################################
+# HTML Files
+################################################################################
+
+DDOC=$(addsuffix .ddoc, macros html dlang.org doc ${GENERATED}/${LATEST}) $(NODATETIME)
+STD_DDOC=$(addsuffix .ddoc, macros html dlang.org ${GENERATED}/${LATEST} std std_navbar-release ${GENERATED}/modlist-${LATEST}) $(NODATETIME)
+STD_DDOC_PRE=$(addsuffix .ddoc, macros html dlang.org ${GENERATED}/${LATEST} std std_navbar-prerelease ${GENERATED}/modlist-prerelease) $(NODATETIME)
+SPEC_DDOC=${DDOC} spec/spec.ddoc
+CHANGELOG_DDOC=${DDOC} changelog/changelog.ddoc $(NODATETIME)
+CHANGELOG_PRE_DDOC=${CHANGELOG_DDOC} changelog/prerelease.ddoc
+
 PREMADE=appendices.html articles.html fetch-issue-cnt.php howtos.html	\
 language-reference.html robots.txt .htaccess .dpl_rewrite_map.txt	\
 d-keyring.gpg
@@ -197,7 +182,9 @@ $(PREMADE) $(STYLES) $(IMAGES) $(JAVASCRIPT))
 
 ALL_FILES = $(ALL_FILES_BUT_SITEMAP) $(DOC_OUTPUT_DIR)/sitemap.html
 
+################################################################################
 # Pattern rulez
+################################################################################
 
 # NOTE: Depending on the version of make, order matters here. Therefore, put
 # sub-directories before their parents.
@@ -362,7 +349,7 @@ dlangspec.verbatim.txt : $(DMD) verbatim.ddoc dlangspec-consolidated.d
 ../%-${DUB_VER} :
 	git clone --depth=1 -b v${DUB_VER} ${GIT_HOME}/$* $@
 
-${DMD_DIR} ${DRUNTIME_DIR} ${PHOBOS_DIR} :
+${DMD_DIR} ${DRUNTIME_DIR} ${PHOBOS_DIR} ${TOOLS_DIR} ${INSTALLER_DIR}:
 	git clone --depth=1 ${GIT_HOME}/$(@F) $@
 
 ################################################################################
@@ -411,7 +398,7 @@ ${DOC_OUTPUT_DIR}/phobos-prerelease/object.verbatim : $(DMD)
 ################################################################################
 
 .PHONY: phobos-prerelease
-phobos-prerelease : ${PHOBOS_DIR_GENERATED} $(STD_DDOC_PRE) druntime-prerelease
+phobos-prerelease : ${PHOBOS_FILES_GENERATED} $(STD_DDOC_PRE) druntime-prerelease
 	${MAKE} --directory=${PHOBOS_DIR_GENERATED} -f posix.mak \
 	  STDDOC="$(addprefix `pwd`/, $(STD_DDOC_PRE))" \
 	  DOC_OUTPUT_DIR="${DOC_OUTPUT_DIR}/phobos-prerelease" \
@@ -421,7 +408,7 @@ phobos-prerelease : ${PHOBOS_DIR_GENERATED} $(STD_DDOC_PRE) druntime-prerelease
 	  VERSION="$(realpath ${DMD_DIR}/VERSION)" \
 	  html -j4
 
-phobos-release : ${PHOBOS_STABLE_DIR_GENERATED} $(DMD_REL) $(STD_DDOC) \
+phobos-release : ${PHOBOS_STABLE_FILES_GENERATED} $(DMD_REL) $(STD_DDOC) \
 		druntime-release
 	${MAKE} --directory=${PHOBOS_STABLE_DIR_GENERATED} -f posix.mak \
 	  DMD=$(DMD_REL) \
@@ -434,7 +421,7 @@ phobos-release : ${PHOBOS_STABLE_DIR_GENERATED} $(DMD_REL) $(STD_DDOC) \
 	  VERSION="$(realpath ${DMD_DIR}/VERSION)" \
 	  html -j4
 
-phobos-prerelease-verbatim : ${PHOBOS_DIR_GENERATED} ${DOC_OUTPUT_DIR}/phobos-prerelease/index.verbatim
+phobos-prerelease-verbatim : ${PHOBOS_FILES_GENERATED} ${DOC_OUTPUT_DIR}/phobos-prerelease/index.verbatim
 ${DOC_OUTPUT_DIR}/phobos-prerelease/index.verbatim : verbatim.ddoc \
 	    ${DOC_OUTPUT_DIR}/phobos-prerelease/object.verbatim
 	${MAKE} --directory=${PHOBOS_DIR_GENERATED} -f posix.mak \
@@ -483,7 +470,7 @@ ${DOC_OUTPUT_DIR}/library-prerelease/.htaccess : dpl_prerelease_htaccess
 	cp $< $@
 
 docs.json : ${DMD_REL} ${DRUNTIME_STABLE_DIR} \
-		${PHOBOS_STABLE_DIR_GENERATED} | dpl-docs
+		${PHOBOS_STABLE_FILES_GENERATED} | dpl-docs
 	find ${DRUNTIME_STABLE_DIR}/src -name '*.d' | \
 	  sed -e /unittest.d/d -e /gcstub/d > .release-files.txt
 	find ${PHOBOS_STABLE_DIR_GENERATED} -name '*.d' | \
@@ -495,7 +482,7 @@ docs.json : ${DMD_REL} ${DRUNTIME_STABLE_DIR} \
 	rm .release-files.txt .release-dummy.html
 
 docs-prerelease.json : ${DMD} ${DRUNTIME_DIR} \
-		${PHOBOS_DIR_GENERATED} | dpl-docs
+		${PHOBOS_FILES_GENERATED} | dpl-docs
 	find ${DRUNTIME_DIR}/src -name '*.d' | sed -e '/gcstub/d' \
 	  -e /unittest/d > .prerelease-files.txt
 	find ${PHOBOS_DIR_GENERATED} -name '*.d' | sed -e /unittest.d/d \
@@ -551,30 +538,28 @@ d.tag : chmgen.d $(STABLE_DMD) $(ALL_FILES) phobos-release druntime-release
 #
 # - This transforms assert(a = b) to writeln(a); // b
 # - It creates a copy of Phobos to apply the transformations
+# - All "d" files are piped through the transformator,
+#   other needed files (e.g. posix.mak) get copied over
 ################################################################################
 
-$(GENERATED):
-	mkdir -p $@
+ASSERT_WRITELN_BIN = $(GENERATED)/assert_writeln_magic
 
-# --update allows to copy only the newer files and thus only propagate these
-#  changes
-HAS_RSYNC := $(shell command -v rsync 2> /dev/null)
+$(ASSERT_WRITELN_BIN): assert_writeln_magic.d $(DUB)
+	@mkdir -p $(dir $@)
+	$(DUB) build --single $<
+	@mv ./assert_writeln_magic $@
 
-${PHOBOS_DIR_GENERATED}: $(wildcard ${PHOBOS_DIR}/**/*) $(DUB) | $(GENERATED)
-ifdef HAS_RSYNC
-	rsync -a --exclude='.git/' --exclude='generated/' --update -v $(PHOBOS_DIR)/ $@
-else
-	cp -r -T -f $(PHOBOS_DIR) $@
-endif
-	$(DUB) run --single ./assert_writeln_magic.d -- -i $@
+$(PHOBOS_FILES_GENERATED): $(PHOBOS_DIR_GENERATED)/%: $(PHOBOS_DIR)/% $(DUB) $(ASSERT_WRITELN_BIN)
+	@mkdir -p $(dir $@)
+	@if [ $(subst .,, $(suffix $@)) == "d" ] && [ "$@" != "$(PHOBOS_DIR_GENERATED)/index.d" ] ; then \
+		$(ASSERT_WRITELN_BIN) -i $< -o $@ ; \
+	else cp $< $@ ; fi
 
-${PHOBOS_STABLE_DIR_GENERATED}: $(wildcard ${PHOBOS_STABLE_DIR_GENERATED}/**/*) $(DUB) | $(GENERATED)
-ifdef HAS_RSYNC
-	rsync -a --exclude='.git/' --exclude='generated/' --update -v $(PHOBOS_STABLE_DIR)/ $@
-else
-	cp -r -T -f $(PHOBOS_STABLE_DIR) $@
-endif
-	$(DUB) run --single ./assert_writeln_magic.d -- -i $@
+$(PHOBOS_STABLE_FILES_GENERATED): $(PHOBOS_STABLE_DIR_GENERATED)/%: $(PHOBOS_STABLE_DIR)/% $(DUB) $(ASSERT_WRITELN_BIN)
+	@mkdir -p $(dir $@)
+	@if [ $(subst .,, $(suffix $@)) == "d" ] && [ "$@" != "$(PHOBOS_STABLE_DIR_GENERATED)/index.d" ] ; then \
+		$(ASSERT_WRITELN_BIN) -i $< -o $@ ; \
+	else cp $< $@ ; fi
 
 ################################################################################
 # Style tests
@@ -595,10 +580,4 @@ changelog/${NEXT_VERSION}.dd: ${STABLE_DMD} ../tools ../installer
 pending_changelog: changelog/${NEXT_VERSION}.dd html
 	@echo "Please open file:///$(shell pwd)/web/changelog/${NEXT_VERSION}.html in your browser"
 
-../tools:
-	git clone https://github.com/dlang/tools ../tools
-
-../installer:
-	git clone https://github.com/dlang/installer ../installer
-
 .DELETE_ON_ERROR: # GNU Make directive (delete output files on error)