slither-doctor: add new PATH checks

This ensures PATH is correctly configured, and hints the user about
what they might need to do to configure it correctly.

slither/tools/doctor/checks/__init__.py

@@ -1,6 +1,7 @@
 from typing import Callable, List
 from dataclasses import dataclass
 
+from slither.tools.doctor.checks.paths import check_slither_path
 from slither.tools.doctor.checks.platform import compile_project, detect_platform
 from slither.tools.doctor.checks.versions import show_versions
 
@@ -12,6 +13,7 @@ class Check:
 
 
 ALL_CHECKS: List[Check] = [
+    Check("PATH configuration", check_slither_path),
     Check("Software versions", show_versions),
     Check("Project platform", detect_platform),
     Check("Project compilation", compile_project),

slither/tools/doctor/checks/paths.py

@@ -0,0 +1,56 @@
+from pathlib import Path
+from typing import List, Optional, Tuple
+import shutil
+import sysconfig
+
+from slither.utils.colors import yellow, green, red
+
+
+def check_path_config(name: str) -> Tuple[bool, Optional[Path], List[Path]]:
+    binary_path = shutil.which(name)
+    possible_paths = []
+
+    for scheme in sysconfig.get_scheme_names():
+        script_path = Path(sysconfig.get_path("scripts", scheme))
+        purelib_path = Path(sysconfig.get_path("purelib", scheme))
+        script_binary_path = shutil.which(name, path=script_path)
+        if script_binary_path is not None:
+            possible_paths.append((script_path, purelib_path))
+
+    binary_here = False
+    if binary_path is not None:
+        binary_path = Path(binary_path)
+        this_code = Path(__file__)
+        this_binary = list(filter(lambda x: this_code.is_relative_to(x[1]), possible_paths))
+        binary_here = len(this_binary) > 0 and all(
+            binary_path.is_relative_to(script) for script, _ in this_binary
+        )
+
+    return binary_here, binary_path, list(set(script for script, _ in possible_paths))
+
+
+def check_slither_path(**_kwargs) -> None:
+    binary_here, binary_path, possible_paths = check_path_config("slither")
+    show_paths = False
+
+    if binary_path:
+        print(green(f"`slither` found in PATH at `{binary_path}`."))
+        if binary_here:
+            print(green("Its location matches this slither-doctor installation."))
+        else:
+            print(
+                yellow(
+                    f"This path does not correspond to this slither-doctor installation.\n"
+                    + "Double-check the order of directories in PATH if you have several slither installations."
+                )
+            )
+            show_paths = True
+    else:
+        print(red("`slither` was not found in PATH."))
+        show_paths = True
+
+    if show_paths:
+        print()
+        print("Consider adding one of the following directories to PATH:")
+        for path in possible_paths:
+            print(f"  * {path}")