Use new PythonEnvironment::find_interpreter() function

Summary:
This diff finishes the functionality required to get venv working without having an interpreter sourced.

In this diff, we switch to the new `PythonEnvironment::find_interpreter()` function when an interpreter is not provided to search for the interpreter to use. This replaces the call to get the default interpreter, which is used as a final fallback in the `find_interpreter()` function instead.

Reviewed By: stroxler

Differential Revision: D74366025

fbshipit-source-id: 084e06f49458d25178d382f0adf1d3228fbd361d

Author: connernilsen

pyrefly/lib/config/config.rs

@@ -60,6 +60,15 @@ pub enum ConfigSource {
     Synthetic,
 }
 
+impl ConfigSource {
+    pub fn path<'a>(&'a self) -> Option<&'a Path> {
+        match &self {
+            Self::File(path) => Some(path),
+            Self::Synthetic => None,
+        }
+    }
+}
+
 /// Where the importable Python code in a project lives. There are two common Python project layouts, src and flat.
 /// See: https://packaging.python.org/en/latest/discussions/src-layout-vs-flat-layout/#src-layout-vs-flat-layout
 #[derive(Default)]
@@ -361,12 +370,10 @@ impl ConfigFile {
     /// which should probably be everything except for `PathBuf` or `Globs` types.
     pub fn configure(&mut self) {
         if self.python_environment.any_empty() {
-            if let Some(interpreter) = self
-                .python_interpreter
-                .as_deref()
-                .or(PythonEnvironment::get_default_interpreter())
-            {
-                let system_env = PythonEnvironment::get_interpreter_env(interpreter);
+            if let Some(interpreter) = self.python_interpreter.clone().or_else(|| {
+                PythonEnvironment::find_interpreter(self.source.path().and_then(|p| p.parent()))
+            }) {
+                let system_env = PythonEnvironment::get_interpreter_env(&interpreter);
                 self.python_environment.override_empty(system_env);
             } else {
                 self.python_environment.set_empty_to_default();

test/basic.md

@@ -137,3 +137,17 @@ $ mkdir $TMPDIR/foo && touch $TMPDIR/foo/bar.py && echo "x: str = 0" > $TMPDIR/f
  INFO 0 errors* (glob)
 [0]
 ```
+
+## We can find a venv interpreter, even when not sourced
+
+```scrut {output_stream: stderr}
+$ python3 -m venv $TMPDIR/venv && \
+> echo "import third_party.test2" > $TMPDIR/test.py && \
+> export site_packages=$($TMPDIR/venv/bin/python -c "import site; print(site.getsitepackages()[0])") && \
+> mkdir $site_packages/third_party && \
+> echo "x = 1" > $site_packages/third_party/test2.py && \
+> touch $TMPDIR/pyrefly.toml && \
+> $PYREFLY check $TMPDIR/test.py
+ INFO 0 errors* (glob)
+[0]
+```