BLI Path: add function BLI_path_contains()

Add function `BLI_path_contains(container, containee)` that returns true
if and only `container` contains `containee`.

Paths are normalised and converted to native path separators before
comparing. Relative paths are *not* made absolute, to simplify the
function call; if this is necessary the caller has to do this conversion
first.

source/blender/blenlib/BLI_path_util.h

@@ -55,6 +55,10 @@ bool BLI_path_name_at_index(const char *__restrict path,
                             int *__restrict r_offset,
                             int *__restrict r_len) ATTR_NONNULL() ATTR_WARN_UNUSED_RESULT;
 
+/** Return true only if #containee_path is contained in #container_path. */
+bool BLI_path_contains(const char *container_path,
+                       const char *containee_path) ATTR_WARN_UNUSED_RESULT;
+
 const char *BLI_path_slash_rfind(const char *string) ATTR_NONNULL() ATTR_WARN_UNUSED_RESULT;
 int BLI_path_slash_ensure(char *string) ATTR_NONNULL();
 void BLI_path_slash_rstrip(char *string) ATTR_NONNULL();

source/blender/blenlib/intern/path_util.c

@@ -1935,6 +1935,34 @@ bool BLI_path_name_at_index(const char *__restrict path,
   return false;
 }
 
+bool BLI_path_contains(const char *container_path, const char *containee_path)
+{
+  char container_native[PATH_MAX];
+  char containee_native[PATH_MAX];
+
+  /* Keep space for a trailing slash. If the path is truncated by this, the containee path is
+   * longer than PATH_MAX and the result is ill-defined.  */
+  BLI_strncpy(container_native, container_path, PATH_MAX - 1);
+  BLI_strncpy(containee_native, containee_path, PATH_MAX);
+
+  BLI_path_slash_native(container_native);
+  BLI_path_slash_native(containee_native);
+
+  BLI_path_normalize(NULL, container_native);
+  BLI_path_normalize(NULL, containee_native);
+
+  if (STREQ(container_native, containee_native)) {
+    /* The paths are equal, they contain each other. */
+    return true;
+  }
+
+  /* Add a trailing slash to prevent same-prefix directories from matching.
+   * e.g. "/some/path" doesn't contain "/some/pathlib". */
+  BLI_path_slash_ensure(container_native);
+
+  return BLI_str_startswith(containee_native, container_native);
+}
+
 /**
  * Returns pointer to the leftmost path separator in string. Not actually used anywhere.
  */

source/blender/blenlib/tests/BLI_path_util_test.cc

@@ -655,3 +655,26 @@ TEST(path_util, PathRelPath)
 #  undef PATH_REL
 
 #endif
+
+/* BLI_path_contains */
+TEST(path_util, PathContains)
+{
+  EXPECT_TRUE(BLI_path_contains("/some/path", "/some/path")) << "A path contains itself";
+  EXPECT_TRUE(BLI_path_contains("/some/path", "/some/path/inside"))
+      << "A path contains its subdirectory";
+  EXPECT_TRUE(BLI_path_contains("/some/path", "/some/path/../path/inside"))
+      << "Paths should be normalised";
+  EXPECT_TRUE(BLI_path_contains("C:\\some\\path", "C:\\some\\path\\inside"))
+      << "Windows paths should be supported as well";
+
+  EXPECT_FALSE(BLI_path_contains("C:\\some\\path", "C:\\some\\other\\path"))
+      << "Windows paths should be supported as well";
+  EXPECT_FALSE(BLI_path_contains("/some/path", "/"))
+      << "Root directory not be contained in a subdirectory";
+  EXPECT_FALSE(BLI_path_contains("/some/path", "/some/path/../outside"))
+      << "Paths should be normalised";
+  EXPECT_FALSE(BLI_path_contains("/some/path", "/some/path_library"))
+      << "Just sharing a suffix is not enough, path semantics should be followed";
+  EXPECT_FALSE(BLI_path_contains("/some/path", "./contents"))
+      << "Relative paths are not supported";
+}