Windows: fix off-by-one errors with MAX_PATH

In almost every place we compared paths against
MAX_PATH, we had it wrong. MAX_PATH is the
null-terminated maximum length, so paths exactly
MAX_PATH long (not counting the null-terminator)
were incorrectly considered short.

Also fix the error message in the MSVC python
wrapper, because it reported an incorrect path
length limit in the warning message.

See https://github.com/bazelbuild/bazel/issues/2107

--
PiperOrigin-RevId: 146762382
MOS_MIGRATED_REVID=146762382

2 files changed, 7 insertions, 5 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/windows/WindowsFileOperations.java b/src/main/java/com/google/devtools/build/lib/windows/WindowsFileOperations.java
index 516c29ec0e..4750ff5962 100644
--- a/src/main/java/com/google/devtools/build/lib/windows/WindowsFileOperations.java
+++ b/src/main/java/com/google/devtools/build/lib/windows/WindowsFileOperations.java
@@ -42,6 +42,8 @@ public class WindowsFileOperations {
     // Prevent construction
   }
 
+  private static final int MAX_PATH = 260;
+
   // Keep IS_JUNCTION_* values in sync with src/main/native/windows_file_operations.cc.
   private static final int IS_JUNCTION_YES = 0;
   private static final int IS_JUNCTION_NO = 1;
@@ -91,11 +93,11 @@ public class WindowsFileOperations {
   /**
    * Returns a Windows-style path suitable to pass to unicode WinAPI functions.
    *
-   * <p>Returns an UNC path if `path` is longer than `MAX_PATH` (in <windows.h>). If it's shorter or
-   * is already an UNC path, then this method returns `path` itself.
+   * <p>Returns an UNC path if `path` is at least `MAX_PATH` long. If it's shorter or is already an
+   * UNC path, then this method returns `path` itself.
    */
   static String asLongPath(String path) {
-    return path.length() > 260 && !path.startsWith("\\\\?\\")
+    return path.length() >= MAX_PATH && !path.startsWith("\\\\?\\")
         ? ("\\\\?\\" + path.replace('/', '\\'))
         : path;
   }
diff --git a/src/main/java/com/google/devtools/build/lib/windows/WindowsSubprocessFactory.java b/src/main/java/com/google/devtools/build/lib/windows/WindowsSubprocessFactory.java
index ae8b495cfd..0632baca01 100644
--- a/src/main/java/com/google/devtools/build/lib/windows/WindowsSubprocessFactory.java
+++ b/src/main/java/com/google/devtools/build/lib/windows/WindowsSubprocessFactory.java
@@ -69,8 +69,8 @@ public class WindowsSubprocessFactory implements Subprocess.Factory {
 
   public String processArgv0(String argv0) {
     // Normalize the path and make it Windows-style.
-    // If argv0 is longer than MAX_PATH (260 chars), createNativeProcess calls GetShortPathNameW to
-    // obtain a 8dot3 name for it (thereby support long paths in CreateProcessA), but then argv0
+    // If argv0 is at least MAX_PATH (260 chars) long, createNativeProcess calls GetShortPathNameW
+    // to obtain a 8dot3 name for it (thereby support long paths in CreateProcessA), but then argv0
     // must be prefixed with "\\?\" for GetShortPathNameW to work, so it also must be an absolute,
     // normalized, Windows-style path.
     // Therefore if it's absolute, then normalize it also.