Rollup merge of #142627 - Kobzol:bootstrap-metadata, r=jieyouxu

Add `StepMetadata` to describe steps

This is used to replace the previous downcasting of executed steps, which wasn't very scalable. In addition to tests, we could also use the metadata e.g. for tracing.

r? ```@jieyouxu```

5 files changed, 83 insertions, 45 deletions

diff --git a/src/bootstrap/src/core/build_steps/compile.rs b/src/bootstrap/src/core/build_steps/compile.rs
index 52f421b4782..f6efb23e8d8 100644
--- a/src/bootstrap/src/core/build_steps/compile.rs
+++ b/src/bootstrap/src/core/build_steps/compile.rs
@@ -24,7 +24,8 @@ use crate::core::build_steps::tool::SourceType;
 use crate::core::build_steps::{dist, llvm};
 use crate::core::builder;
 use crate::core::builder::{
-    Builder, Cargo, Kind, PathSet, RunConfig, ShouldRun, Step, TaskPath, crate_description,
+    Builder, Cargo, Kind, PathSet, RunConfig, ShouldRun, Step, StepMetadata, TaskPath,
+    crate_description,
 };
 use crate::core::config::{DebuginfoLevel, LlvmLibunwind, RustcLto, TargetSelection};
 use crate::utils::build_stamp;
@@ -305,6 +306,14 @@ impl Step for Std {
             builder.compiler(compiler.stage, builder.config.host_target),
         ));
     }
+
+    fn metadata(&self) -> Option<StepMetadata> {
+        Some(
+            StepMetadata::build("std", self.target)
+                .built_by(self.compiler)
+                .stage(self.compiler.stage),
+        )
+    }
 }
 
 fn copy_and_stamp(
@@ -1171,6 +1180,14 @@ impl Step for Rustc {
 
         build_compiler.stage
     }
+
+    fn metadata(&self) -> Option<StepMetadata> {
+        Some(
+            StepMetadata::build("rustc", self.target)
+                .built_by(self.build_compiler)
+                .stage(self.build_compiler.stage + 1),
+        )
+    }
 }
 
 pub fn rustc_cargo(
diff --git a/src/bootstrap/src/core/build_steps/llvm.rs b/src/bootstrap/src/core/build_steps/llvm.rs
index 8f2f143c352..de67a5f77e6 100644
--- a/src/bootstrap/src/core/build_steps/llvm.rs
+++ b/src/bootstrap/src/core/build_steps/llvm.rs
@@ -18,7 +18,7 @@ use build_helper::git::PathFreshness;
 #[cfg(feature = "tracing")]
 use tracing::instrument;
 
-use crate::core::builder::{Builder, RunConfig, ShouldRun, Step};
+use crate::core::builder::{Builder, RunConfig, ShouldRun, Step, StepMetadata};
 use crate::core::config::{Config, TargetSelection};
 use crate::utils::build_stamp::{BuildStamp, generate_smart_stamp_hash};
 use crate::utils::exec::command;
@@ -582,6 +582,10 @@ impl Step for Llvm {
 
         res
     }
+
+    fn metadata(&self) -> Option<StepMetadata> {
+        Some(StepMetadata::build("llvm", self.target))
+    }
 }
 
 pub fn get_llvm_version(builder: &Builder<'_>, llvm_config: &Path) -> String {
diff --git a/src/bootstrap/src/core/builder/mod.rs b/src/bootstrap/src/core/builder/mod.rs
index 7433f0b0f3b..b26f47a3171 100644
--- a/src/bootstrap/src/core/builder/mod.rs
+++ b/src/bootstrap/src/core/builder/mod.rs
@@ -130,6 +130,38 @@ pub trait Step: 'static + Clone + Debug + PartialEq + Eq + Hash {
         // as such calling them from ./x.py isn't logical.
         unimplemented!()
     }
+
+    /// Returns metadata of the step, for tests
+    fn metadata(&self) -> Option<StepMetadata> {
+        None
+    }
+}
+
+/// Metadata that describes an executed step, mostly for testing and tracing.
+#[allow(unused)]
+#[derive(Debug)]
+pub struct StepMetadata {
+    name: &'static str,
+    kind: Kind,
+    target: TargetSelection,
+    built_by: Option<Compiler>,
+    stage: Option<u32>,
+}
+
+impl StepMetadata {
+    pub fn build(name: &'static str, target: TargetSelection) -> Self {
+        Self { name, kind: Kind::Build, target, built_by: None, stage: None }
+    }
+
+    pub fn built_by(mut self, compiler: Compiler) -> Self {
+        self.built_by = Some(compiler);
+        self
+    }
+
+    pub fn stage(mut self, stage: u32) -> Self {
+        self.stage = Some(stage);
+        self
+    }
 }
 
 pub struct RunConfig<'a> {
diff --git a/src/bootstrap/src/core/builder/tests.rs b/src/bootstrap/src/core/builder/tests.rs
index d07df7f4a84..6268a2b59d6 100644
--- a/src/bootstrap/src/core/builder/tests.rs
+++ b/src/bootstrap/src/core/builder/tests.rs
@@ -8,6 +8,7 @@ use super::*;
 use crate::Flags;
 use crate::core::build_steps::doc::DocumentationFormat;
 use crate::core::config::Config;
+use crate::utils::cache::ExecutedStep;
 use crate::utils::tests::git::{GitCtx, git_test};
 
 static TEST_TRIPLE_1: &str = "i686-unknown-haiku";
@@ -1258,31 +1259,24 @@ mod staging {
 /// Renders the executed bootstrap steps for usage in snapshot tests with insta.
 /// Only renders certain important steps.
 /// Each value in `steps` should be a tuple of (Step, step output).
-fn render_steps(steps: &[(Box<dyn Any>, Box<dyn Any>)]) -> String {
+fn render_steps(steps: &[ExecutedStep]) -> String {
     steps
         .iter()
-        .filter_map(|(step, output)| {
-            // FIXME: implement an optional method on Step to produce metadata for test, instead
-            // of this downcasting
-            if let Some((rustc, output)) = downcast_step::<compile::Rustc>(step, output) {
-                Some(format!(
-                    "[build] {} -> {}",
-                    render_compiler(rustc.build_compiler),
-                    // FIXME: return the correct stage from the `Rustc` step, now it behaves weirdly
-                    render_compiler(Compiler::new(rustc.build_compiler.stage + 1, rustc.target)),
-                ))
-            } else if let Some((std, output)) = downcast_step::<compile::Std>(step, output) {
-                Some(format!(
-                    "[build] {} -> std {} <{}>",
-                    render_compiler(std.compiler),
-                    std.compiler.stage,
-                    std.target
-                ))
-            } else if let Some((llvm, output)) = downcast_step::<llvm::Llvm>(step, output) {
-                Some(format!("[build] llvm <{}>", llvm.target))
-            } else {
-                None
+        .filter_map(|step| {
+            use std::fmt::Write;
+
+            let Some(metadata) = &step.metadata else {
+                return None;
+            };
+
+            let mut record = format!("[{}] ", metadata.kind.as_str());
+            if let Some(compiler) = metadata.built_by {
+                write!(record, "{} -> ", render_compiler(compiler));
             }
+            let stage =
+                if let Some(stage) = metadata.stage { format!("{stage} ") } else { "".to_string() };
+            write!(record, "{} {stage}<{}>", metadata.name, metadata.target);
+            Some(record)
         })
         .map(|line| {
             line.replace(TEST_TRIPLE_1, "target1")
@@ -1293,19 +1287,6 @@ fn render_steps(steps: &[(Box<dyn Any>, Box<dyn Any>)]) -> String {
         .join("\n")
 }
 
-fn downcast_step<'a, S: Step>(
-    step: &'a Box<dyn Any>,
-    output: &'a Box<dyn Any>,
-) -> Option<(&'a S, &'a S::Output)> {
-    let Some(step) = step.downcast_ref::<S>() else {
-        return None;
-    };
-    let Some(output) = output.downcast_ref::<S::Output>() else {
-        return None;
-    };
-    Some((step, output))
-}
-
 fn render_compiler(compiler: Compiler) -> String {
     format!("rustc {} <{}>", compiler.stage, compiler.host)
 }
diff --git a/src/bootstrap/src/utils/cache.rs b/src/bootstrap/src/utils/cache.rs
index 0c737470958..5098e2f03c4 100644
--- a/src/bootstrap/src/utils/cache.rs
+++ b/src/bootstrap/src/utils/cache.rs
@@ -218,10 +218,15 @@ pub struct Cache {
         >,
     >,
     #[cfg(test)]
-    /// Contains steps in the same order in which they were executed
-    /// Useful for tests
-    /// Tuples (step, step output)
-    executed_steps: RefCell<Vec<(Box<dyn Any>, Box<dyn Any>)>>,
+    /// Contains step metadata of executed steps (in the same order in which they were executed).
+    /// Useful for tests.
+    executed_steps: RefCell<Vec<ExecutedStep>>,
+}
+
+#[cfg(test)]
+#[derive(Debug)]
+pub struct ExecutedStep {
+    pub metadata: Option<crate::core::builder::StepMetadata>,
 }
 
 impl Cache {
@@ -243,9 +248,8 @@ impl Cache {
 
         #[cfg(test)]
         {
-            let step: Box<dyn Any> = Box::new(step.clone());
-            let output: Box<dyn Any> = Box::new(value.clone());
-            self.executed_steps.borrow_mut().push((step, output));
+            let metadata = step.metadata();
+            self.executed_steps.borrow_mut().push(ExecutedStep { metadata });
         }
 
         stepcache.insert(step, value);
@@ -283,7 +287,7 @@ impl Cache {
     }
 
     #[cfg(test)]
-    pub fn into_executed_steps(mut self) -> Vec<(Box<dyn Any>, Box<dyn Any>)> {
+    pub fn into_executed_steps(mut self) -> Vec<ExecutedStep> {
         mem::take(&mut self.executed_steps.borrow_mut())
     }
 }