needs_rebuild: don't open files on Windows when checking timestamps

nob.c

@@ -21,6 +21,7 @@ const char *test_names[] = {
     "bytes_for_utf8",
     "sv_foreach",
     "svlit_at_different_storages",
+    "needs_rebuild_locked_file",
 };
 #define test_names_count ARRAY_LEN(test_names)
 

nob.h

@@ -2459,41 +2459,34 @@ NOBDEF const char *nob_temp_sv_to_cstr(Nob_String_View sv)
 NOBDEF int nob_needs_rebuild(const char *output_path, const char **input_paths, size_t input_paths_count)
 {
 #ifdef _WIN32
-    BOOL bSuccess;
-
-    HANDLE output_path_fd = CreateFile(output_path, GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_READONLY, NULL);
-    if (output_path_fd == INVALID_HANDLE_VALUE) {
+    // NOTE: GetFileAttributesEx() reads only the file metadata and never
+    // opens the file, so it cannot fail just because an editor or an
+    // antivirus has the file open. CreateFile() with dwShareMode=0 used to
+    // fail with ERROR_SHARING_VIOLATION in that case, which the POSIX
+    // stat() implementation below is not susceptible to.
+    WIN32_FILE_ATTRIBUTE_DATA file_attributes = {0};
+
+    if (GetFileAttributesExA(output_path, GetFileExInfoStandard, &file_attributes) == 0) {
         // NOTE: if output does not exist it 100% must be rebuilt
-        if (GetLastError() == ERROR_FILE_NOT_FOUND) return 1;
-        nob_log(NOB_ERROR, "Could not open file %s: %s", output_path, nob_win32_error_message(GetLastError()));
-        return -1;
-    }
-    FILETIME output_path_time;
-    bSuccess = GetFileTime(output_path_fd, NULL, NULL, &output_path_time);
-    CloseHandle(output_path_fd);
-    if (!bSuccess) {
-        nob_log(NOB_ERROR, "Could not get time of %s: %s", output_path, nob_win32_error_message(GetLastError()));
+        if (GetLastError() == ERROR_FILE_NOT_FOUND)
+            return 1;
+        nob_log(NOB_ERROR, "Could not get file attributes of %s: %s", output_path, nob_win32_error_message(GetLastError()));
         return -1;
     }
+    FILETIME output_path_time = file_attributes.ftLastWriteTime;
 
     for (size_t i = 0; i < input_paths_count; ++i) {
         const char *input_path = input_paths[i];
-        HANDLE input_path_fd = CreateFile(input_path, GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_READONLY, NULL);
-        if (input_path_fd == INVALID_HANDLE_VALUE) {
+        if (GetFileAttributesExA(input_path, GetFileExInfoStandard, &file_attributes) == 0) {
             // NOTE: non-existing input is an error cause it is needed for building in the first place
-            nob_log(NOB_ERROR, "Could not open file %s: %s", input_path, nob_win32_error_message(GetLastError()));
-            return -1;
-        }
-        FILETIME input_path_time;
-        bSuccess = GetFileTime(input_path_fd, NULL, NULL, &input_path_time);
-        CloseHandle(input_path_fd);
-        if (!bSuccess) {
-            nob_log(NOB_ERROR, "Could not get time of %s: %s", input_path, nob_win32_error_message(GetLastError()));
+            nob_log(NOB_ERROR, "Could not get file attributes of %s: %s", input_path, nob_win32_error_message(GetLastError()));
             return -1;
         }
+        FILETIME input_path_time = file_attributes.ftLastWriteTime;
 
         // NOTE: if even a single input_path is fresher than output_path that's 100% rebuild
-        if (CompareFileTime(&input_path_time, &output_path_time) == 1) return 1;
+        if (CompareFileTime(&input_path_time, &output_path_time) == 1)
+            return 1;
     }
 
     return 0;

tests/needs_rebuild_locked_file.c

@@ -0,0 +1,51 @@
+#include "shared.h"
+
+#ifdef _WIN32
+    #include <windows.h>
+#else
+    #include <time.h>
+#endif
+
+int main(void)
+{
+    // The harness runs tests in a fresh temp cwd.
+    const char *output_path = "output.txt";
+    const char *input_path  = "input.txt";
+
+    // Write the output first, then the input, so the input is strictly
+    // fresher than the output and needs_rebuild() must return 1.
+    if (!write_entire_file(output_path, "output", 6)) return 1;
+
+    // Make sure the input file gets a strictly fresher timestamp than the
+    // output file regardless of the filesystem timestamp resolution.
+#ifdef _WIN32
+    Sleep(100);
+#else
+    struct timespec ts = {0, 100000000};
+    nanosleep(&ts, NULL);
+#endif
+
+    if (!write_entire_file(input_path, "input", 5)) return 1;
+
+#ifdef _WIN32
+    // Hold the input file the way an editor or an AV scanner would. With
+    // dwShareMode = 0 nobody else may open it, not even for reading, so
+    // needs_rebuild() must not rely on opening the file.
+    HANDLE lock = CreateFileA(input_path, GENERIC_READ, 0, NULL,
+                              OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
+    if (lock == INVALID_HANDLE_VALUE) {
+        fprintf(stderr, "could not lock %s (err=%lu)\n", input_path, GetLastError());
+        return 1;
+    }
+#endif // _WIN32
+
+    // Must NOT fail just because the input file is locked.
+    int result = needs_rebuild(output_path, &input_path, 1);
+    printf("needs_rebuild = %d\n", result);
+
+#ifdef _WIN32
+    CloseHandle(lock);
+#endif // _WIN32
+
+    return 0;
+}

tests/needs_rebuild_locked_file.stdout.txt

@@ -0,0 +1 @@
+needs_rebuild = 1

tests/needs_rebuild_locked_file.win32.stdout.txt

@@ -0,0 +1 @@
+needs_rebuild = 1