1 files changed, 102 insertions, 0 deletions
diff --git a/src/main/java/com/google/devtools/build/lib/actions/SingleStringArgFormatter.java b/src/main/java/com/google/devtools/build/lib/actions/SingleStringArgFormatter.java
new file mode 100644
index 0000000000..b4b3d028d0
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/actions/SingleStringArgFormatter.java
@@ -0,0 +1,102 @@
+// Copyright 2018 The Bazel Authors. All rights reserved.
+//
+// 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.
+package com.google.devtools.build.lib.actions;
+
+/**
+ * Implementation of a formatter that supports only a single '%s'
+ *
+ * <p>This implementation is used in command line item expansions that use formatting. We use a
+ * custom implementation to improve performance and avoid GC.
+ */
+public class SingleStringArgFormatter {
+
+  /**
+   * Returns true if the format string contains a single '%s'.
+   *
+   * <p>%% escape sequences are supported.
+   */
+  public static boolean isValid(String formatStr) {
+    return onlyOccurrence(formatStr, formatStr.length()) != -1;
+  }
+
+  /**
+   * Returns the equivalent result of <code>String.format(formatStr, subject)</code>, under the
+   * assumption that the format string contains a single %s.
+   *
+   * <p>Use {@link #isValid} to validate the format string.
+   *
+   * @throws IllegalArgumentException if the format string is invalid.
+   */
+  public static String format(String formatStr, String subject) {
+    int n = formatStr.length();
+    int idx = onlyOccurrence(formatStr, n);
+    if (idx < 0) {
+      throw new IllegalArgumentException(
+          "Expected format string with single '%s', found: " + formatStr);
+    }
+    return new StringBuilder(n + subject.length() - 2)
+        .append(formatStr, 0, idx)
+        .append(subject)
+        .append(formatStr, idx + 2, n)
+        .toString();
+  }
+
+  /*
+   * Returns the index of the only occurrence of %s. Skips any %%. Returns -1 if {@code formatStr}
+   * is malformed.
+   */
+  private static int onlyOccurrence(String formatStr, int n) {
+    int idx = nextOccurrence(formatStr, n, 0);
+    if (idx < 0) {
+      return -1;
+    }
+    // Only one occurrence please
+    if (nextOccurrence(formatStr, n, idx + 2) != -1) {
+      return -1;
+    }
+    return idx;
+  }
+
+  /**
+   * Returns next occurrence of %s. Skips any %%.
+   *
+   * @return
+   *     <li>[0-n]: Index of next %s
+   *     <li>-1: No %s found until end of string
+   *     <li>-2: Illegal sequence found, eg. %f
+   */
+  private static int nextOccurrence(String formatStr, int n, int idx) {
+    while (idx < n) {
+      idx = formatStr.indexOf('%', idx);
+      if (idx == -1) {
+        break;
+      }
+      if ((idx + 1) < n) {
+        char c = formatStr.charAt(idx + 1);
+        if (c == 's') {
+          return idx;
+        }
+        if (c != '%') {
+          // Illegal sequence found
+          return -2;
+        }
+        idx += 2;
+      } else {
+        // Terminating '%' found, illegal
+        return -2;
+      }
+    }
+    return -1;
+  }
+}