Resolve non-abs/rel exec paths wrt. to PATH

Author: fangerer

graalpython/com.oracle.graal.python.shell/src/com/oracle/graal/python/shell/GraalPythonMain.java

@@ -35,6 +35,7 @@
 import java.lang.management.ManagementFactory;
 import java.nio.file.Files;
 import java.nio.file.NoSuchFileException;
+import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.HashMap;
@@ -356,16 +357,78 @@ private static String getLauncherExecName() {
         if (ImageInfo.inImageCode()) {
             String binPathName = null;
             if (ProcessProperties.getArgumentVectorBlockSize() > 0) {
-                binPathName = ProcessProperties.getArgumentVectorProgramName();
+                binPathName = calculateProgramFullPath(ProcessProperties.getArgumentVectorProgramName());
             }
             if (binPathName != null) {
-                return Paths.get(binPathName).toAbsolutePath().toString();
+                return binPathName;
             }
             return ProcessProperties.getExecutableName();
         }
         return GraalPythonMain.BASH_LAUNCHER_EXEC_NAME;
     }
 
+    /**
+     * Follows the same semantics as CPython's {@code getpath.c:calculate_program_full_path} to
+     * determine the full program path if we just got a non-absolute program name. This method
+     * handles the following cases:
+     * <dl>
+     * <dt><b>Program name is an absolute path</b></dt>
+     * <dd>Just return {@code program}.</dd>
+     * <dt><b>Program name is a relative path</b></dt>
+     * <dd>it will resolve it to an absolute path. E.g. {@code "./python3"} will become {@code 
+     * "<current_working_dir>/python3"}/dd>
+     * <dt><b>Program name is neither an absolute nor a relative path</b></dt>
+     * <dd>It will resolve the program name wrt. to the {@code PATH} env variable. Since it may be
+     * that the {@code PATH} variable is not available, this method will return {@code null}</dd>
+     * </dl>
+     * 
+     * @param program The program name as passed in the process' argument vector (position 0).
+     * @return The absolute path to the program or {@code null}.
+     */
+    private static String calculateProgramFullPath(String program) {
+        Path programPath = Paths.get(program);
+
+        // If this is an absolute path, we are already fine.
+        if (programPath.isAbsolute()) {
+            return program;
+        }
+
+        /*
+         * If there is no slash in the arg[0] path, then we have to assume python is on the user's
+         * $PATH, since there's no other way to find a directory to start the search from. If $PATH
+         * isn't exported, you lose.
+         */
+        if (programPath.getNameCount() < 2) {
+            // Resolve the program name with respect to the PATH variable.
+            String path = System.getenv("PATH");
+            if (path != null) {
+                int last = 0;
+                for (int i = path.indexOf(File.pathSeparatorChar); i != -1; i = path.indexOf(File.pathSeparatorChar, last)) {
+                    Path resolvedProgramName = Paths.get(path.substring(last, i)).resolve(programPath);
+                    if (Files.isExecutable(resolvedProgramName)) {
+                        return resolvedProgramName.toString();
+                    }
+
+                    // next start is the char after the separator because we have "path0:path1" and
+                    // 'i' points to ':'
+                    last = i + 1;
+                }
+            }
+            return null;
+        }
+        // It's seemingly a relative path, so we can just resolve it to an absolute one.
+        assert !programPath.isAbsolute();
+        /*
+         * Another special case (see: CPython function "getpath.c:copy_absolute"): If the program
+         * name starts with "./" (on Unix; or similar on other systems) then the path is
+         * canonicalized.
+         */
+        if (".".equals(programPath.getName(0).toString())) {
+            return programPath.toAbsolutePath().normalize().toString();
+        }
+        return programPath.toAbsolutePath().toString();
+    }
+
     private String[] getExecutableList() {
         String launcherExecName = getLauncherExecName();
         if (launcherExecName != null) {