From 75ee4afec9dbab835e21f0ad3394899ff58030c1 Mon Sep 17 00:00:00 2001
From: Jeroen Ketema <jketema@github.com>
Date: Tue, 7 Jul 2026 10:45:29 +0200
Subject: [PATCH] Kotlin: Resolve `subst`ed drives on Windows

---
 .../java/com/semmle/util/files/FileUtil.java  |  7 +-
 .../com/semmle/util/files/SubstResolver.java  | 77 +++++++++++++++++++
 2 files changed, 81 insertions(+), 3 deletions(-)
 create mode 100644 java/kotlin-extractor/src/main/java/com/semmle/util/files/SubstResolver.java

diff --git a/java/kotlin-extractor/src/main/java/com/semmle/util/files/FileUtil.java b/java/kotlin-extractor/src/main/java/com/semmle/util/files/FileUtil.java
index 79ce2d8d8d3..19bdc786c5e 100644
--- a/java/kotlin-extractor/src/main/java/com/semmle/util/files/FileUtil.java
+++ b/java/kotlin-extractor/src/main/java/com/semmle/util/files/FileUtil.java
@@ -1237,13 +1237,14 @@ public class FileUtil
 
 	/**
 	 * Try to convert a file into a canonical file. Handles the possible IO exception by just making
-	 * the path absolute.
+	 * the path absolute. Also resolves subst drives on Windows.
 	 */
 	public static File tryMakeCanonical (File f)
 	{
 		try {
-			return f.getCanonicalFile();
-		}
+			// getCanonicalFile does not canonicalize subst drives on Windows, so do this separately. This
+			// is a no-op on non-Windows platforms.
+			return SubstResolver.resolve(f.getCanonicalFile());		}
 		catch (IOException ignored) {
 			Exceptions.ignore(ignored, "Can't log error: Could be too verbose.");
 			return new File(simplifyPath(f));
diff --git a/java/kotlin-extractor/src/main/java/com/semmle/util/files/SubstResolver.java b/java/kotlin-extractor/src/main/java/com/semmle/util/files/SubstResolver.java
new file mode 100644
index 00000000000..3d93c45234d
--- /dev/null
+++ b/java/kotlin-extractor/src/main/java/com/semmle/util/files/SubstResolver.java
@@ -0,0 +1,77 @@
+package com.semmle.util.files;
+
+import java.io.File;
+import java.net.URISyntaxException;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Resolves Windows {@code subst}ed drive letters to their underlying paths. On non-Windows
+ * platforms, or when the native library failed to load, resolving will be a no-op.
+ */
+public class SubstResolver {
+  private static final boolean available;
+
+  static {
+    boolean loaded = false;
+    if (File.separatorChar == '\\') {
+      String dist = System.getenv("CODEQL_DIST");
+    if (dist != null && !dist.isEmpty()) {
+        try {
+          Path library = Paths.get(dist).resolve("tools")
+                  .resolve("win64").resolve("canonicalize.dll").toAbsolutePath();
+          System.load(library.toString());
+          loaded = true;
+        } catch (RuntimeException | UnsatisfiedLinkError ignored) {
+        }
+      }
+    }
+    available = loaded;
+  }
+
+  private SubstResolver() {}
+
+  /**
+   * Given a drive root like {@code "X:\\"} (or {@code "X:/"}), returns the path that drive is
+   * {@code subst}ed to, or {@code null} if the drive root was not subst drive or if an internal
+   * error occurred.
+   */
+  private static native String nativeResolveSubst(String driveRoot);
+
+  /**
+   * If {@code f} is an absolute path starting with a {@code subst}ed drive letter, return an
+   * equivalent path with the drive letter replaced by its target. Otherwise return {@code f}
+   * unchanged.
+   */
+  public static File resolve(File f) {
+    if (!available) {
+      return f;
+    }
+    String path = f.getPath();
+    if (path.length() < 3 || path.charAt(1) != ':') {
+      return f;
+    }
+    char sep = path.charAt(2);
+    if (sep != '\\' && sep != '/') {
+      return f;
+    }
+    if (!isDriveLetter(path.charAt(0))) {
+      return f;
+    }
+
+    String resolved = nativeResolveSubst(path.substring(0, 3));
+    if (resolved == null) {
+      return f;
+    }
+
+    // Append the remainder of the original path. The native side strips away
+    // any trailing separator.
+    return new File(resolved + path.substring(2));
+  }
+
+  private static boolean isDriveLetter(char c) {
+    return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
+  }
+}