Add subst resolution for Kotlin and Go extractors

java/kotlin-extractor/src/main/java/com/semmle/util/files/FileUtil.java

@@ -1242,12 +1242,13 @@ public class FileUtil
 	public static File tryMakeCanonical (File f)
 	{
 		try {
-			return f.getCanonicalFile();
+			f = f.getCanonicalFile();
 		}
 		catch (IOException ignored) {
 			Exceptions.ignore(ignored, "Can't log error: Could be too verbose.");
-			return new File(simplifyPath(f));
+			f = new File(simplifyPath(f));
 		}
+		return SubstResolver.resolve(f);
 	}
 
 

java/kotlin-extractor/src/main/java/com/semmle/util/files/SubstResolver.java

@@ -0,0 +1,76 @@
+package com.semmle.util.files;
+
+import java.io.File;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+/**
+ * Resolves Windows {@code subst}ed drive letters to their underlying paths. On non-Windows
+ * platforms, or when the native library failed to load, {@link #resolve(File)} is a no-op that
+ * returns its argument unchanged.
+ */
+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:\\"}, returns the path that drive is
+	 * {@code subst}ed to, or {@code null} if the letter isn't a subst mapping.
+	 */
+	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;
+		}
+
+		return new File(resolved + path.substring(2));
+	}
+
+	private static boolean isDriveLetter(char c) {
+		return (c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z');
+	}
+
+	public static boolean isAvailable() {
+		return available;
+	}
+}