doc: improve error message for missing Rust compiler (#117)

Author: davidhewitt

setuptools_rust/command.py

@@ -25,7 +25,15 @@ def run(self):
 
         all_optional = all(ext.optional for ext in self.extensions)
         try:
-            version = get_rust_version()
+            version = get_rust_version(
+                min_version=max(
+                    filter(
+                        lambda version: version is not None,
+                        (ext.get_rust_version() for ext in self.extensions),
+                    ),
+                    default=None
+                )
+            )
         except DistutilsPlatformError as e:
             if not all_optional:
                 raise

setuptools_rust/extension.py

@@ -123,7 +123,7 @@ def get_rust_version(self):
         if self.rust_version is None:
             return None
         try:
-            return semantic_version.Spec(self.rust_version)
+            return semantic_version.SimpleSpec.parse(self.rust_version)
         except ValueError:
             raise DistutilsSetupError(
                 "Can not parse rust compiler version: %s", self.rust_version

setuptools_rust/utils.py

@@ -57,12 +57,32 @@ def rust_features(ext=True, binding=Binding.PyO3):
         raise DistutilsPlatformError(f"unknown Rust binding: '{binding}'")
 
 
-def get_rust_version():
+def get_rust_version(min_version=None):
     try:
         output = subprocess.check_output(["rustc", "-V"]).decode("latin-1")
         return semantic_version.Version(output.split(" ")[1], partial=True)
     except (subprocess.CalledProcessError, OSError):
-        raise DistutilsPlatformError("can't find Rust compiler")
+        raise DistutilsPlatformError(
+            "can't find Rust compiler\n\n"
+            "If you are using an outdated pip version, it is possible a "
+            "prebuilt wheel is available for this package but pip is not able "
+            "to install from it. Installing from the wheel would avoid the "
+            "need for a Rust compiler.\n\n"
+            "To update pip, run:\n\n"
+            "    pip install --upgrade pip\n\n"
+            "and then retry package installation.\n\n"
+            "If you did intend to build this package from source, try "
+            "installing a Rust compiler from your system package manager and "
+            "ensure it is on the PATH during installation. Alternatively, "
+            "rustup (available at https://rustup.rs) is the recommended way "
+            "to download and update the Rust compiler toolchain."
+            + (
+
+                f"\n\nThis package requires Rust {min_version}."
+                if min_version is not None
+                else ""
+            )
+        )
     except Exception as exc:
         raise DistutilsPlatformError(f"can't get rustc version: {str(exc)}")