Delegate to ./pants when [DEFAULT] delegate_bootstrap=true. (#75)

The choice of config section for the `pants.toml` config file was made
to have something that won't choke the regular Pants configuration
verification and also not show up in any online help.

Closes #33

When `delegate_bootstrap=true` in the `[DEFAULT]` section of 
`pants.toml` _and_ `pants_version` is unspecified (`PANTS_SHA` 
is also considered here) bootstrapping Pants is delegated to `./pants`.

Author: kaos

.github/workflows/ci.yml

@@ -52,7 +52,7 @@ jobs:
         uses: actions/cache@v3
         with:
           path: ${{ env.SCIE_PANTS_DEV_CACHE }}
-          key: ${{ runner.os }}-${{ runner.arch }}-scie-pants-v1
+          key: ${{ runner.os }}-${{ runner.arch }}-scie-pants-v2
       - name: Build, Package & Integration Tests
         if: ${{ matrix.os == 'macOS-11-ARM64' }}
         run: |

package/src/main.rs

@@ -797,6 +797,12 @@ fn test(
     tools_pex_mismatch_warn: bool,
 ) -> ExitResult {
     build_step!("Running smoke tests");
+    log!(
+        Color::Yellow,
+        "Disabling pants rc files for the smoke tests."
+    );
+    env::set_var("PANTS_PANTSRC", "False");
+
     // Max Python supported is 3.9 and only Linux x86_64 and macOS aarch64 and x86_64 wheels were
     // released.
     if matches!(
@@ -1019,7 +1025,7 @@ index 81e3bd7..4236f4b 100755
 
  function activate_venv() {
 diff --git a/pants b/pants
-index b422eff..df13536 100755
+index b422eff..16f0cf5 100755
 --- a/pants
 +++ b/pants
 @@ -70,4 +70,5 @@ function exec_pants_bare() {
@@ -1028,6 +1034,17 @@ index b422eff..df13536 100755
 
 +echo >&2 "Pants from sources argv: $@."
  exec_pants_bare "$@"
+diff --git a/pants.toml b/pants.toml
+index ab5cba1..8432bb2 100644
+--- a/pants.toml
++++ b/pants.toml
+@@ -1,3 +1,6 @@
++[DEFAULT]
++delegate_bootstrap = true
++
+ [GLOBAL]
+ print_stacktrace = true
+
 diff --git a/src/python/pants/VERSION b/src/python/pants/VERSION
 index b70ae75..271706a 100644
 --- a/src/python/pants/VERSION
@@ -1113,6 +1130,28 @@ index b70ae75..271706a 100644
                 .current_dir(user_repo_dir),
             "The pants_from_sources mode is working.",
         )?;
+
+        integration_test!("Verify delegating to `./pants`.");
+        let result = execute(
+            Command::new(scie_pants_scie)
+                .arg("-V")
+                .env("SCIE_PANTS_TEST_MODE", "delegate_bootstrap mode")
+                .current_dir(pants_2_14_1_clone_dir)
+                .stderr(Stdio::piped()),
+        )?;
+        let stderr = String::from_utf8(result.stderr).map_err(|e| {
+            Code::FAILURE.with_message(format!("Failed to decode Pants stderr: {e}"))
+        })?;
+        let expected_message = "The delegate_bootstrap mode is working.";
+        assert!(
+            stderr.contains(expected_message),
+            "STDERR did not contain '{expected_message}':\n{stderr}"
+        );
+        let expected_argv_message = "Pants from sources argv: -V.";
+        assert!(
+            stderr.contains(expected_argv_message),
+            "STDERR did not contain '{expected_argv_message}':\n{stderr}"
+        );
     }
 
     // Max Python supported is 3.8 and only Linux and macOS x86_64 wheels were released.

src/config.rs

@@ -20,12 +20,19 @@ pub(crate) struct DebugPy {
     pub(crate) version: Option<String>,
 }
 
+#[derive(Default, Deserialize)]
+pub(crate) struct Default {
+    pub(crate) delegate_bootstrap: Option<bool>,
+}
+
 #[derive(Deserialize)]
 pub(crate) struct Config {
     #[serde(default, rename = "GLOBAL")]
     pub(crate) global: Global,
     #[serde(default)]
     pub(crate) debugpy: DebugPy,
+    #[serde(default, rename = "DEFAULT")]
+    pub(crate) default: Default,
 }
 
 pub(crate) struct PantsConfig {
@@ -45,6 +52,10 @@ impl PantsConfig {
     pub(crate) fn debugpy_version(&self) -> Option<String> {
         self.config.debugpy.version.clone()
     }
+
+    pub(crate) fn delegate_bootstrap(&self) -> bool {
+        self.config.default.delegate_bootstrap.unwrap_or_default()
+    }
 }
 
 impl PantsConfig {

src/main.rs

@@ -98,15 +98,16 @@ fn find_pants_installation() -> Result<Option<PantsConfig>> {
 #[time("debug", "scie-pants::{}")]
 fn get_pants_process() -> Result<Process> {
     let pants_installation = find_pants_installation()?;
-    let (build_root, configured_pants_version, debugpy_version) =
+    let (build_root, configured_pants_version, debugpy_version, delegate_bootstrap) =
         if let Some(ref pants_config) = pants_installation {
             (
                 Some(pants_config.build_root().to_path_buf()),
                 pants_config.package_version(),
                 pants_config.debugpy_version(),
+                pants_config.delegate_bootstrap(),
             )
         } else {
-            (None, None, None)
+            (None, None, None, false)
         };
 
     let env_pants_sha = env_version("PANTS_SHA")?;
@@ -126,6 +127,17 @@ fn get_pants_process() -> Result<Process> {
         None
     };
 
+    if delegate_bootstrap && pants_version == None {
+        let exe = build_root
+            .expect("Failed to locate build root")
+            .join("pants")
+            .into_os_string();
+        return Ok(Process {
+            exe,
+            ..Default::default()
+        });
+    }
+
     info!("Found Pants build root at {build_root:?}");
     info!("The required Pants version is {pants_version:?}");