AAPT2: Fix file::mkdirs when given absolute paths

file::mkdirs would try to extract the first part of the
path '/path' which would be the empty string ''. Mkdir would
fail creating the empty string directory.

Change-Id: Ice8ba92135f145f52f3663499a2c49eebe797328
diff --git a/tools/aapt2/util/Files.cpp b/tools/aapt2/util/Files.cpp
index 04e8199..6428e98 100644
--- a/tools/aapt2/util/Files.cpp
+++ b/tools/aapt2/util/Files.cpp
@@ -96,7 +96,7 @@
     const char* start = path.begin();
     const char* end = path.end();
     for (const char* current = start; current != end; ++current) {
-        if (*current == sDirSep) {
+        if (*current == sDirSep && current != start) {
             StringPiece parentPath(start, current - start);
             int result = mkdirImpl(parentPath);
             if (result < 0 && errno != EEXIST) {
@@ -139,6 +139,20 @@
     return {};
 }
 
+void appendPath(std::string* base, StringPiece part) {
+    assert(base);
+    const bool baseHasTrailingSep = (!base->empty() && *(base->end() - 1) == sDirSep);
+    const bool partHasLeadingSep = (!part.empty() && *(part.begin()) == sDirSep);
+    if (baseHasTrailingSep && partHasLeadingSep) {
+        // Remove the part's leading sep
+        part = part.substr(1, part.size() - 1);
+    } else if (!baseHasTrailingSep && !partHasLeadingSep) {
+        // None of the pieces has a separator.
+        *base += sDirSep;
+    }
+    base->append(part.data(), part.size());
+}
+
 std::string packageToPath(const StringPiece& package) {
     std::string outPath;
     for (StringPiece part : util::tokenize<char>(package, '.')) {
diff --git a/tools/aapt2/util/Files.h b/tools/aapt2/util/Files.h
index c58ba5d..c2e6115 100644
--- a/tools/aapt2/util/Files.h
+++ b/tools/aapt2/util/Files.h
@@ -61,14 +61,7 @@
 /*
  * Appends a path to `base`, separated by the directory separator.
  */
-void appendPath(std::string* base, const StringPiece& part);
-
-/*
- * Appends a series of paths to `base`, separated by the
- * system directory separator.
- */
-template <typename... Ts >
-void appendPath(std::string* base, const StringPiece& part, const Ts&... parts);
+void appendPath(std::string* base, StringPiece part);
 
 /*
  * Makes all the directories in `path`. The last element in the path
@@ -139,20 +132,6 @@
     std::vector<std::string> mPatternTokens;
 };
 
-inline void appendPath(std::string* base, const StringPiece& part) {
-    assert(base);
-    *base += sDirSep;
-    base->append(part.data(), part.size());
-}
-
-template <typename... Ts >
-void appendPath(std::string* base, const StringPiece& part, const Ts&... parts) {
-    assert(base);
-    *base += sDirSep;
-    base->append(part.data(), part.size());
-    appendPath(base, parts...);
-}
-
 } // namespace file
 } // namespace aapt
 
diff --git a/tools/aapt2/util/Files_test.cpp b/tools/aapt2/util/Files_test.cpp
new file mode 100644
index 0000000..efb0459
--- /dev/null
+++ b/tools/aapt2/util/Files_test.cpp
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "test/Test.h"
+#include "util/Files.h"
+
+#include <sstream>
+
+namespace aapt {
+namespace file {
+
+class FilesTest : public ::testing::Test {
+public:
+    void SetUp() override {
+        std::stringstream builder;
+        builder << "hello" << sDirSep << "there";
+        mExpectedPath = builder.str();
+    }
+
+protected:
+    std::string mExpectedPath;
+};
+
+TEST_F(FilesTest, appendPath) {
+    std::string base = "hello";
+    appendPath(&base, "there");
+    EXPECT_EQ(mExpectedPath, base);
+}
+
+TEST_F(FilesTest, appendPathWithLeadingOrTrailingSeparators) {
+    std::string base = "hello/";
+    appendPath(&base, "there");
+    EXPECT_EQ(mExpectedPath, base);
+
+    base = "hello";
+    appendPath(&base, "/there");
+    EXPECT_EQ(mExpectedPath, base);
+
+    base = "hello/";
+    appendPath(&base, "/there");
+    EXPECT_EQ(mExpectedPath, base);
+}
+
+} // namespace files
+} // namespace aapt