Add test verifying that changing comments recompiles dependents

Author: yaahc

compiler/rustc_metadata/src/creader.rs

@@ -35,7 +35,7 @@ use rustc_session::search_paths::PathKind;
 use rustc_span::edition::Edition;
 use rustc_span::{DUMMY_SP, Ident, Span, Symbol, sym};
 use rustc_target::spec::{PanicStrategy, Target, TargetTuple};
-use tracing::{debug, info, trace};
+use tracing::{debug, info, instrument, trace};
 
 use crate::errors;
 use crate::locator::{CrateError, CrateLocator, CratePaths};
@@ -168,7 +168,7 @@ impl<'a> std::fmt::Debug for CrateDump<'a> {
 }
 
 /// Reason that a crate is being sourced as a dependency.
-#[derive(Clone, Copy)]
+#[derive(Clone, Copy, Debug)]
 enum CrateOrigin<'a> {
     /// This crate was a dependency of another crate.
     IndirectDependency {
@@ -779,6 +779,7 @@ impl<'a, 'tcx> CrateLoader<'a, 'tcx> {
         }
     }
 
+    #[instrument(level = "debug", skip(self))]
     fn maybe_resolve_crate<'b>(
         &'b mut self,
         name: Symbol,

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -585,7 +585,8 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
             adapted.set_some(on_disk_index, self.lazy(adapted_source_file));
         }
 
-        adapted.encode(&mut self.opaque)
+        let ret = adapted.encode(&mut self.opaque);
+        ret
     }
 
     fn encode_crate_root(&mut self) -> LazyValue<CrateRoot> {

compiler/rustc_metadata/src/rmeta/mod.rs

@@ -332,7 +332,7 @@ impl RawDefId {
     }
 }
 
-#[derive(Encodable, Decodable)]
+#[derive(Encodable, Decodable, Debug)]
 pub(crate) struct CrateDep {
     pub name: Symbol,
     pub hash: Svh,

tests/run-make/rdr-ignores-comments/after.rs

@@ -0,0 +1,8 @@
+#![crate_name = "foo"]
+#![crate_type = "lib"]
+// bbb
+pub struct Foo;
+
+impl Foo {
+    pub fn bar(self: Foo) {}
+}

tests/run-make/rdr-ignores-comments/before.rs

@@ -0,0 +1,8 @@
+#![crate_name = "foo"]
+#![crate_type = "lib"]
+// aaa
+pub struct Foo;
+
+impl Foo {
+    pub fn bar(self: Foo) {}
+}

tests/run-make/rdr-ignores-comments/manual_diff.sh

@@ -0,0 +1,9 @@
+#! /bin/bash
+x test tests/run-make/rdr-ignores-comments
+cp before.rs foo.rs
+rustc +stage1 --emit=metadata ./foo.rs && mv libfoo.rmeta before.rmeta
+cp after.rs foo.rs
+rustc +stage1 --emit=metadata ./foo.rs && mv libfoo.rmeta after.rmeta
+rm foo.rs
+vbindiff before.rmeta after.rmeta
+rm before.rmeta after.rmeta

tests/run-make/rdr-ignores-comments/rmake.rs

@@ -0,0 +1,25 @@
+// tests that we can reuse an existing rlib instead of rebuilding
+// when changin a non-doc comments in a file
+use run_make_support::{rfs, rustc};
+use std::path::Path;
+use std::hash::{Hash, Hasher};
+
+fn main() {
+    let before = check_and_hash("before.rs");
+    let after = check_and_hash("after.rs");
+    dbg!(before, after);
+    assert_eq!(before, after);
+}
+
+fn check_and_hash<P>(filename: P) -> u64
+where
+    P: AsRef<Path>,
+{
+    rfs::rename(filename, "foo.rs");
+    rustc().input("foo.rs").emit("metadata").run();
+    // hash the output
+    let bytes = rfs::read("libfoo.rmeta");
+    let mut hasher = std::hash::DefaultHasher::new();
+    bytes.hash(&mut hasher);
+    hasher.finish()
+}