Move the filetest harness into its own crate.

This allows us to run the tests via a library call rather than just
as a command execution. And, it's a step toward a broader goal, which
is to keep the code in the top-level src directory minimal, with
important functionality exposed as crates.

lib/filetests/src/test_verifier.rs

@@ -0,0 +1,82 @@
+//! Test command for checking the IL verifier.
+//!
+//! The `test verifier` test command looks for annotations on instructions like this:
+//!
+//! ```cton
+//!     jump ebb3 ; error: jump to non-existent EBB
+//! ```
+//!
+//! This annotation means that the verifier is expected to given an error for the jump instruction
+//! containing the substring "jump to non-existent EBB".
+
+use std::borrow::{Borrow, Cow};
+use cretonne::verify_function;
+use cretonne::ir::Function;
+use cton_reader::TestCommand;
+use subtest::{SubTest, Context, Result};
+use match_directive::match_directive;
+
+struct TestVerifier;
+
+pub fn subtest(parsed: &TestCommand) -> Result<Box<SubTest>> {
+    assert_eq!(parsed.command, "verifier");
+    if !parsed.options.is_empty() {
+        Err(format!("No options allowed on {}", parsed))
+    } else {
+        Ok(Box::new(TestVerifier))
+    }
+}
+
+impl SubTest for TestVerifier {
+    fn name(&self) -> Cow<str> {
+        Cow::from("verifier")
+    }
+
+    fn needs_verifier(&self) -> bool {
+        // Running the verifier before this test would defeat its purpose.
+        false
+    }
+
+    fn run(&self, func: Cow<Function>, context: &Context) -> Result<()> {
+        let func = func.borrow();
+
+        // Scan source annotations for "error:" directives.
+        let mut expected = None;
+        for comment in &context.details.comments {
+            if let Some(tail) = match_directive(comment.text, "error:") {
+                // Currently, the verifier can only report one problem at a time.
+                // Reject more than one `error:` directives.
+                if expected.is_some() {
+                    return Err("cannot handle multiple error: directives".to_string());
+                }
+                expected = Some((comment.entity, tail));
+            }
+        }
+
+        match verify_function(func, context.flags_or_isa()) {
+            Ok(_) => {
+                match expected {
+                    None => Ok(()),
+                    Some((_, msg)) => Err(format!("passed, expected error: {}", msg)),
+                }
+            }
+            Err(got) => {
+                match expected {
+                    None => Err(format!("verifier pass, got {}", got)),
+                    Some((want_loc, want_msg)) if got.message.contains(want_msg) => {
+                        if want_loc == got.location {
+                            Ok(())
+                        } else {
+                            Err(format!(
+                                "correct error reported on {}, but wanted {}",
+                                got.location,
+                                want_loc
+                            ))
+                        }
+                    }
+                    Some(_) => Err(format!("mismatching error: {}", got)),
+                }
+            }
+        }
+    }
+}