Add an option to fall back to cargo test

cargo-insta/src/cli.rs

@@ -211,6 +211,8 @@ struct TestCommand {
     /// Picks the test runner.
     #[arg(long, default_value = "auto")]
     test_runner: TestRunner,
+    #[arg(long)]
+    test_runner_fallback: Option<bool>,
     /// Delete unreferenced snapshots after a successful test run.
     #[arg(long, hide = true)]
     delete_unreferenced_snapshots: bool,
@@ -616,9 +618,20 @@ fn test_run(mut cmd: TestCommand, color: ColorWhen) -> Result<(), Box<dyn Error>
         TestRunner::CargoTest => TestRunner::CargoTest,
         TestRunner::Nextest => TestRunner::Nextest,
     };
-
-    let (mut proc, snapshot_ref_file, prevents_doc_run) =
-        prepare_test_runner(test_runner, cmd.unreferenced, &cmd, color, &[], None)?;
+    // Prioritize the command line over the tool config
+    let test_runner_fallback = cmd
+        .test_runner_fallback
+        .unwrap_or(loc.tool_config.test_runner_fallback());
+
+    let (mut proc, snapshot_ref_file, prevents_doc_run) = prepare_test_runner(
+        test_runner,
+        test_runner_fallback,
+        cmd.unreferenced,
+        &cmd,
+        color,
+        &[],
+        None,
+    )?;
 
     if !cmd.keep_pending {
         process_snapshots(true, None, &loc, Some(Operation::Reject))?;
@@ -631,6 +644,7 @@ fn test_run(mut cmd: TestCommand, color: ColorWhen) -> Result<(), Box<dyn Error>
     if matches!(cmd.test_runner, TestRunner::Nextest) && !prevents_doc_run {
         let (mut proc, _, _) = prepare_test_runner(
             TestRunner::CargoTest,
+            false,
             cmd.unreferenced,
             &cmd,
             color,
@@ -796,6 +810,7 @@ fn handle_unreferenced_snapshots(
 #[allow(clippy::type_complexity)]
 fn prepare_test_runner<'snapshot_ref>(
     test_runner: TestRunner,
+    test_runner_fallback: bool,
     unreferenced: UnreferencedSnapshots,
     cmd: &TestCommand,
     color: ColorWhen,
@@ -806,6 +821,26 @@ fn prepare_test_runner<'snapshot_ref>(
     let cargo = cargo
         .as_deref()
         .unwrap_or_else(|| std::ffi::OsStr::new("cargo"));
+    let test_runner = match test_runner {
+        TestRunner::CargoTest | TestRunner::Auto => test_runner,
+        TestRunner::Nextest => {
+            // Fall back to `cargo test` if `cargo nextest` isn't installed and
+            // `test_runner_fallback` is true (but don't run the cargo command
+            // unless that's an option)
+            if !test_runner_fallback
+                || std::process::Command::new("cargo")
+                    .arg("nextest")
+                    .arg("--version")
+                    .output()
+                    .map(|output| output.status.success())
+                    .unwrap_or(false)
+            {
+                TestRunner::Nextest
+            } else {
+                TestRunner::Auto
+            }
+        }
+    };
     let mut proc = match test_runner {
         TestRunner::CargoTest | TestRunner::Auto => {
             let mut proc = process::Command::new(cargo);

insta/src/env.rs

@@ -104,6 +104,8 @@ pub struct ToolConfig {
     #[cfg(feature = "glob")]
     glob_fail_fast: bool,
     #[cfg(feature = "_cargo_insta_internal")]
+    test_runner_fallback: bool,
+    #[cfg(feature = "_cargo_insta_internal")]
     test_runner: TestRunner,
     #[cfg(feature = "_cargo_insta_internal")]
     test_unreferenced: UnreferencedSnapshots,
@@ -235,6 +237,15 @@ impl ToolConfig {
                 .map_err(|_| Error::Env("INSTA_TEST_RUNNER"))?
             },
             #[cfg(feature = "_cargo_insta_internal")]
+            test_runner_fallback: match env::var("INSTA_TEST_RUNNER_FALLBACK").as_deref() {
+                Err(_) | Ok("") => resolve(&cfg, &["test", "runner_fallback"])
+                    .and_then(|x| x.as_bool())
+                    .unwrap_or(false),
+                Ok("1") => true,
+                Ok("0") => false,
+                _ => return Err(Error::Env("INSTA_RUNNER_FALLBACK")),
+            },
+            #[cfg(feature = "_cargo_insta_internal")]
             test_unreferenced: {
                 resolve(&cfg, &["test", "unreferenced"])
                     .and_then(|x| x.as_str())
@@ -265,6 +276,8 @@ impl ToolConfig {
         })
     }
 
+    // TODO: Do we want all these methods, vs. just allowing access to the fields?
+
     /// Is insta told to force update snapshots?
     pub fn force_update_snapshots(&self) -> bool {
         self.force_update_snapshots
@@ -304,6 +317,11 @@ impl ToolConfig {
         self.test_runner
     }
 
+    /// Whether to fallback to `cargo test` if the test runner isn't available
+    pub fn test_runner_fallback(&self) -> bool {
+        self.test_runner_fallback
+    }
+
     pub fn test_unreferenced(&self) -> UnreferencedSnapshots {
         self.test_unreferenced
     }

insta/src/lib.rs

@@ -224,6 +224,9 @@
 //! test:
 //!   # also set by INSTA_TEST_RUNNER
 //!   runner: "auto" | "cargo-test" | "nextest"
+//!   # whether to fallback to `cargo-test` if `nextest` is not available,
+//!   # also set by INSTA_TEST_RUNNER_FALLBACK, default false
+//!   test_runner_fallback: true/false
 //!   # automatically assume --review was passed to cargo insta test
 //!   auto_review: true/false
 //!   # automatically assume --accept-unseen was passed to cargo insta test