From 167e0fca4e9e5046c3a0d841ad7601ca39b6e95a Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Fri, 29 May 2020 11:47:17 -0400
Subject: [PATCH 1/3] `StableSourceFileId::new_from_pieces` does not need to be
 public.

(and I want to discourage further use of it if possible.)
---
 src/librustc_span/source_map.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/librustc_span/source_map.rs b/src/librustc_span/source_map.rs
index 49e2144b3e380..16747923f80fd 100644
--- a/src/librustc_span/source_map.rs
+++ b/src/librustc_span/source_map.rs
@@ -107,7 +107,7 @@ impl StableSourceFileId {
         )
     }
 
-    pub fn new_from_pieces(
+    fn new_from_pieces(
         name: &FileName,
         name_was_remapped: bool,
         unmapped_path: Option<&FileName>,

From d0db71a812d97cc33ae709ee66e6b2630753976a Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Fri, 29 May 2020 11:31:55 -0400
Subject: [PATCH 2/3] Split payload of FileName::Real to track both real and
 virutalized paths.

Such splits arise from metadata refs into libstd.

This way, we can (in a follow on commit) continue to emit the virtual name into
things like the like the StableSourceFileId that ends up in incremetnal build
artifacts, while still using the devirtualized file path when we want to access
the file.

Note that this commit is intended to be a refactoring; the actual fix to the bug
in question is in a follow-on commit.
---
 src/librustc_expand/base.rs              |  2 +-
 src/librustc_expand/expand.rs            |  2 +-
 src/librustc_expand/module.rs            |  5 ++-
 src/librustc_expand/proc_macro_server.rs |  3 +-
 src/librustc_interface/passes.rs         | 11 ++++--
 src/librustc_metadata/rmeta/decoder.rs   | 25 +++++++-----
 src/librustc_metadata/rmeta/encoder.rs   |  1 +
 src/librustc_save_analysis/span_utils.rs |  5 ++-
 src/librustc_span/lib.rs                 | 48 ++++++++++++++++++++++--
 src/librustc_span/source_map.rs          | 25 ++++++++----
 src/librustdoc/html/render.rs            |  5 ++-
 src/librustdoc/html/render/cache.rs      |  2 +-
 src/librustdoc/html/sources.rs           |  4 +-
 src/librustdoc/test.rs                   |  4 +-
 14 files changed, 103 insertions(+), 39 deletions(-)

diff --git a/src/librustc_expand/base.rs b/src/librustc_expand/base.rs
index 59c1a5468f100..bbd6bb47fb884 100644
--- a/src/librustc_expand/base.rs
+++ b/src/librustc_expand/base.rs
@@ -1086,7 +1086,7 @@ impl<'a> ExtCtxt<'a> {
         if !path.is_absolute() {
             let callsite = span.source_callsite();
             let mut result = match self.source_map().span_to_unmapped_path(callsite) {
-                FileName::Real(path) => path,
+                FileName::Real(name) => name.into_local_path(),
                 FileName::DocTest(path, _) => path,
                 other => {
                     return Err(self.struct_span_err(
diff --git a/src/librustc_expand/expand.rs b/src/librustc_expand/expand.rs
index 2618c758ca5da..39058d229d5f1 100644
--- a/src/librustc_expand/expand.rs
+++ b/src/librustc_expand/expand.rs
@@ -340,7 +340,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         let mut module = ModuleData {
             mod_path: vec![Ident::from_str(&self.cx.ecfg.crate_name)],
             directory: match self.cx.source_map().span_to_unmapped_path(krate.span) {
-                FileName::Real(path) => path,
+                FileName::Real(name) => name.into_local_path(),
                 other => PathBuf::from(other.to_string()),
             },
         };
diff --git a/src/librustc_expand/module.rs b/src/librustc_expand/module.rs
index aad92a09743b3..acf986445e534 100644
--- a/src/librustc_expand/module.rs
+++ b/src/librustc_expand/module.rs
@@ -71,7 +71,7 @@ crate fn parse_external_mod(
     // Extract the directory path for submodules of `module`.
     let path = sess.source_map().span_to_unmapped_path(module.inner);
     let mut path = match path {
-        FileName::Real(path) => path,
+        FileName::Real(name) => name.into_local_path(),
         other => PathBuf::from(other.to_string()),
     };
     path.pop();
@@ -189,7 +189,8 @@ fn error_cannot_declare_mod_here<'a, T>(
     let mut err =
         sess.span_diagnostic.struct_span_err(span, "cannot declare a new module at this location");
     if !span.is_dummy() {
-        if let FileName::Real(src_path) = sess.source_map().span_to_filename(span) {
+        if let FileName::Real(src_name) = sess.source_map().span_to_filename(span) {
+            let src_path = src_name.into_local_path();
             if let Some(stem) = src_path.file_stem() {
                 let mut dest_path = src_path.clone();
                 dest_path.set_file_name(stem);
diff --git a/src/librustc_expand/proc_macro_server.rs b/src/librustc_expand/proc_macro_server.rs
index 5f21ff503d59e..b26f9caf4569c 100644
--- a/src/librustc_expand/proc_macro_server.rs
+++ b/src/librustc_expand/proc_macro_server.rs
@@ -596,7 +596,8 @@ impl server::SourceFile for Rustc<'_> {
     }
     fn path(&mut self, file: &Self::SourceFile) -> String {
         match file.name {
-            FileName::Real(ref path) => path
+            FileName::Real(ref name) => name
+                .local_path()
                 .to_str()
                 .expect("non-UTF8 file path in `proc_macro::SourceFile::path`")
                 .to_string(),
diff --git a/src/librustc_interface/passes.rs b/src/librustc_interface/passes.rs
index 4c054795136b9..61c1e9faa7413 100644
--- a/src/librustc_interface/passes.rs
+++ b/src/librustc_interface/passes.rs
@@ -35,7 +35,7 @@ use rustc_session::output::{filename_for_input, filename_for_metadata};
 use rustc_session::search_paths::PathKind;
 use rustc_session::Session;
 use rustc_span::symbol::Symbol;
-use rustc_span::FileName;
+use rustc_span::{FileName, RealFileName};
 use rustc_trait_selection::traits;
 use rustc_typeck as typeck;
 
@@ -570,13 +570,16 @@ fn write_out_deps(
                 for cnum in resolver.cstore().crates_untracked() {
                     let source = resolver.cstore().crate_source_untracked(cnum);
                     if let Some((path, _)) = source.dylib {
-                        files.push(escape_dep_filename(&FileName::Real(path)));
+                        let file_name = FileName::Real(RealFileName::Named(path));
+                        files.push(escape_dep_filename(&file_name));
                     }
                     if let Some((path, _)) = source.rlib {
-                        files.push(escape_dep_filename(&FileName::Real(path)));
+                        let file_name = FileName::Real(RealFileName::Named(path));
+                        files.push(escape_dep_filename(&file_name));
                     }
                     if let Some((path, _)) = source.rmeta {
-                        files.push(escape_dep_filename(&FileName::Real(path)));
+                        let file_name = FileName::Real(RealFileName::Named(path));
+                        files.push(escape_dep_filename(&file_name));
                     }
                 }
             });
diff --git a/src/librustc_metadata/rmeta/decoder.rs b/src/librustc_metadata/rmeta/decoder.rs
index e1ac4d1341668..cd9816260357a 100644
--- a/src/librustc_metadata/rmeta/decoder.rs
+++ b/src/librustc_metadata/rmeta/decoder.rs
@@ -1485,15 +1485,22 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
 
             if let Some(virtual_dir) = virtual_rust_source_base_dir {
                 if let Some(real_dir) = &sess.real_rust_source_base_dir {
-                    if let rustc_span::FileName::Real(path) = name {
-                        if let Ok(rest) = path.strip_prefix(virtual_dir) {
-                            let new_path = real_dir.join(rest);
-                            debug!(
-                                "try_to_translate_virtual_to_real: `{}` -> `{}`",
-                                path.display(),
-                                new_path.display(),
-                            );
-                            *path = new_path;
+                    if let rustc_span::FileName::Real(old_name) = name {
+                        if let rustc_span::RealFileName::Named(one_path) = old_name {
+                            if let Ok(rest) = one_path.strip_prefix(virtual_dir) {
+                                let virtual_name = one_path.clone();
+                                let new_path = real_dir.join(rest);
+                                debug!(
+                                    "try_to_translate_virtual_to_real: `{}` -> `{}`",
+                                    virtual_name.display(),
+                                    new_path.display(),
+                                );
+                                let new_name = rustc_span::RealFileName::Devirtualized {
+                                    local_path: new_path,
+                                    virtual_name,
+                                };
+                                *old_name = new_name;
+                            }
                         }
                     }
                 }
diff --git a/src/librustc_metadata/rmeta/encoder.rs b/src/librustc_metadata/rmeta/encoder.rs
index 9c9869c85571f..715cb52db1c42 100644
--- a/src/librustc_metadata/rmeta/encoder.rs
+++ b/src/librustc_metadata/rmeta/encoder.rs
@@ -398,6 +398,7 @@ impl<'tcx> EncodeContext<'tcx> {
                     // any relative paths are potentially relative to a
                     // wrong directory.
                     FileName::Real(ref name) => {
+                        let name = name.local_path();
                         let mut adapted = (**source_file).clone();
                         adapted.name = Path::new(&working_dir).join(name).into();
                         adapted.name_hash = {
diff --git a/src/librustc_save_analysis/span_utils.rs b/src/librustc_save_analysis/span_utils.rs
index 6620941c44046..d5f992b0de05d 100644
--- a/src/librustc_save_analysis/span_utils.rs
+++ b/src/librustc_save_analysis/span_utils.rs
@@ -16,12 +16,13 @@ impl<'a> SpanUtils<'a> {
 
     pub fn make_filename_string(&self, file: &SourceFile) -> String {
         match &file.name {
-            FileName::Real(path) if !file.name_was_remapped => {
+            FileName::Real(name) if !file.name_was_remapped => {
+                let path = name.local_path();
                 if path.is_absolute() {
                     self.sess
                         .source_map()
                         .path_mapping()
-                        .map_prefix(path.clone())
+                        .map_prefix(path.into())
                         .0
                         .display()
                         .to_string()
diff --git a/src/librustc_span/lib.rs b/src/librustc_span/lib.rs
index 85a870ae34c11..7a12d7da31f6c 100644
--- a/src/librustc_span/lib.rs
+++ b/src/librustc_span/lib.rs
@@ -49,7 +49,7 @@ use std::cmp::{self, Ordering};
 use std::fmt;
 use std::hash::Hash;
 use std::ops::{Add, Sub};
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::str::FromStr;
 
 use md5::Md5;
@@ -77,11 +77,45 @@ impl Globals {
 
 scoped_tls::scoped_thread_local!(pub static GLOBALS: Globals);
 
+/// FIXME: Perhaps this should not implement Rustc{Decodable, Encodable}
+#[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash, RustcDecodable, RustcEncodable)]
+#[derive(HashStable_Generic)]
+pub enum RealFileName {
+    Named(PathBuf),
+    /// For de-virtualized paths (namely paths into libstd that have been mapped
+    /// to the appropriate spot on the local host's file system),
+    Devirtualized {
+        /// `local_path` is the (host-dependent) local path to the file.
+        local_path: PathBuf,
+        /// `virtual_name` is the stable path rustc will store internally within
+        /// build artifacts.
+        virtual_name: PathBuf,
+    },
+}
+
+impl RealFileName {
+    /// Returns the path suitable for reading from the file system on the local host.
+    pub fn local_path(&self) -> &Path {
+        match self {
+            RealFileName::Named(p)
+            | RealFileName::Devirtualized { local_path: p, virtual_name: _ } => &p,
+        }
+    }
+
+    /// Returns the path suitable for reading from the file system on the local host.
+    pub fn into_local_path(self) -> PathBuf {
+        match self {
+            RealFileName::Named(p)
+            | RealFileName::Devirtualized { local_path: p, virtual_name: _ } => p,
+        }
+    }
+}
+
 /// Differentiates between real files and common virtual files.
 #[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash, RustcDecodable, RustcEncodable)]
 #[derive(HashStable_Generic)]
 pub enum FileName {
-    Real(PathBuf),
+    Real(RealFileName),
     /// Call to `quote!`.
     QuoteExpansion(u64),
     /// Command line.
@@ -103,7 +137,13 @@ impl std::fmt::Display for FileName {
     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         use FileName::*;
         match *self {
-            Real(ref path) => write!(fmt, "{}", path.display()),
+            Real(RealFileName::Named(ref path)) => write!(fmt, "{}", path.display()),
+            // FIXME: might be nice to display both compoments of Devirtualized.
+            // But for now (to backport fix for issue #70924), best to not
+            // perturb diagnostics so its obvious test suite still works.
+            Real(RealFileName::Devirtualized { ref local_path, virtual_name: _ }) => {
+                write!(fmt, "{}", local_path.display())
+            }
             QuoteExpansion(_) => write!(fmt, "<quote expansion>"),
             MacroExpansion(_) => write!(fmt, "<macro expansion>"),
             Anon(_) => write!(fmt, "<anon>"),
@@ -119,7 +159,7 @@ impl std::fmt::Display for FileName {
 impl From<PathBuf> for FileName {
     fn from(p: PathBuf) -> Self {
         assert!(!p.to_string_lossy().ends_with('>'));
-        FileName::Real(p)
+        FileName::Real(RealFileName::Named(p))
     }
 }
 
diff --git a/src/librustc_span/source_map.rs b/src/librustc_span/source_map.rs
index 16747923f80fd..e2ae32f6a1b34 100644
--- a/src/librustc_span/source_map.rs
+++ b/src/librustc_span/source_map.rs
@@ -247,7 +247,7 @@ impl SourceMap {
 
     fn try_new_source_file(
         &self,
-        filename: FileName,
+        mut filename: FileName,
         src: String,
     ) -> Result<Lrc<SourceFile>, OffsetOverflowError> {
         // The path is used to determine the directory for loading submodules and
@@ -257,13 +257,22 @@ impl SourceMap {
         // be empty, so the working directory will be used.
         let unmapped_path = filename.clone();
 
-        let (filename, was_remapped) = match filename {
-            FileName::Real(filename) => {
-                let (filename, was_remapped) = self.path_mapping.map_prefix(filename);
-                (FileName::Real(filename), was_remapped)
+        let was_remapped;
+        if let FileName::Real(real_filename) = &mut filename {
+            match real_filename {
+                RealFileName::Named(path_to_be_remapped)
+                | RealFileName::Devirtualized {
+                    local_path: path_to_be_remapped,
+                    virtual_name: _,
+                } => {
+                    let mapped = self.path_mapping.map_prefix(path_to_be_remapped.clone());
+                    was_remapped = mapped.1;
+                    *path_to_be_remapped = mapped.0;
+                }
             }
-            other => (other, false),
-        };
+        } else {
+            was_remapped = false;
+        }
 
         let file_id =
             StableSourceFileId::new_from_pieces(&filename, was_remapped, Some(&unmapped_path));
@@ -1001,7 +1010,7 @@ impl SourceMap {
     }
     pub fn ensure_source_file_source_present(&self, source_file: Lrc<SourceFile>) -> bool {
         source_file.add_external_src(|| match source_file.name {
-            FileName::Real(ref name) => self.file_loader.read_file(name).ok(),
+            FileName::Real(ref name) => self.file_loader.read_file(name.local_path()).ok(),
             _ => None,
         })
     }
diff --git a/src/librustdoc/html/render.rs b/src/librustdoc/html/render.rs
index b91aab44f10a2..fce5a815fe20b 100644
--- a/src/librustdoc/html/render.rs
+++ b/src/librustdoc/html/render.rs
@@ -465,7 +465,7 @@ pub fn run(
     } = options;
 
     let src_root = match krate.src {
-        FileName::Real(ref p) => match p.parent() {
+        FileName::Real(ref p) => match p.local_path().parent() {
             Some(p) => p.to_path_buf(),
             None => PathBuf::new(),
         },
@@ -1650,9 +1650,10 @@ impl Context {
 
         // We can safely ignore synthetic `SourceFile`s.
         let file = match item.source.filename {
-            FileName::Real(ref path) => path,
+            FileName::Real(ref path) => path.local_path().to_path_buf(),
             _ => return None,
         };
+        let file = &file;
 
         let (krate, path) = if item.source.cnum == LOCAL_CRATE {
             if let Some(path) = self.shared.local_sources.get(file) {
diff --git a/src/librustdoc/html/render/cache.rs b/src/librustdoc/html/render/cache.rs
index 5b09029122718..be800c3c79467 100644
--- a/src/librustdoc/html/render/cache.rs
+++ b/src/librustdoc/html/render/cache.rs
@@ -173,7 +173,7 @@ impl Cache {
         // Cache where all our extern crates are located
         for &(n, ref e) in &krate.externs {
             let src_root = match e.src {
-                FileName::Real(ref p) => match p.parent() {
+                FileName::Real(ref p) => match p.local_path().parent() {
                     Some(p) => p.to_path_buf(),
                     None => PathBuf::new(),
                 },
diff --git a/src/librustdoc/html/sources.rs b/src/librustdoc/html/sources.rs
index c5f44baced2e4..018c0e82c4561 100644
--- a/src/librustdoc/html/sources.rs
+++ b/src/librustdoc/html/sources.rs
@@ -67,10 +67,10 @@ impl<'a> SourceCollector<'a> {
     /// Renders the given filename into its corresponding HTML source file.
     fn emit_source(&mut self, filename: &FileName) -> Result<(), Error> {
         let p = match *filename {
-            FileName::Real(ref file) => file,
+            FileName::Real(ref file) => file.local_path().to_path_buf(),
             _ => return Ok(()),
         };
-        if self.scx.local_sources.contains_key(&**p) {
+        if self.scx.local_sources.contains_key(&*p) {
             // We've already emitted this source
             return Ok(());
         }
diff --git a/src/librustdoc/test.rs b/src/librustdoc/test.rs
index afc1501d7b613..86bba15a6f93f 100644
--- a/src/librustdoc/test.rs
+++ b/src/librustdoc/test.rs
@@ -663,7 +663,7 @@ impl Collector {
             let filename = source_map.span_to_filename(self.position);
             if let FileName::Real(ref filename) = filename {
                 if let Ok(cur_dir) = env::current_dir() {
-                    if let Ok(path) = filename.strip_prefix(&cur_dir) {
+                    if let Ok(path) = filename.local_path().strip_prefix(&cur_dir) {
                         return path.to_owned().into();
                     }
                 }
@@ -693,7 +693,7 @@ impl Tester for Collector {
         // FIXME(#44940): if doctests ever support path remapping, then this filename
         // needs to be the result of `SourceMap::span_to_unmapped_path`.
         let path = match &filename {
-            FileName::Real(path) => path.clone(),
+            FileName::Real(path) => path.local_path().to_path_buf(),
             _ => PathBuf::from(r"doctest.rs"),
         };
 

From 0d19fb3bf64f3b41139005c05a9435129f645263 Mon Sep 17 00:00:00 2001
From: "Felix S. Klock II" <pnkfelix@pnkfx.org>
Date: Fri, 29 May 2020 14:04:03 -0400
Subject: [PATCH 3/3] Use the virtual name for libstd files in
 StableSourceFileId and also in the encoded build artifacts.

Fix #70924.
---
 src/librustc_metadata/rmeta/encoder.rs |  2 +-
 src/librustc_span/lib.rs               | 13 +++++++++++++
 src/librustc_span/source_map.rs        | 11 ++++++++++-
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/librustc_metadata/rmeta/encoder.rs b/src/librustc_metadata/rmeta/encoder.rs
index 715cb52db1c42..b739882b7aa96 100644
--- a/src/librustc_metadata/rmeta/encoder.rs
+++ b/src/librustc_metadata/rmeta/encoder.rs
@@ -398,7 +398,7 @@ impl<'tcx> EncodeContext<'tcx> {
                     // any relative paths are potentially relative to a
                     // wrong directory.
                     FileName::Real(ref name) => {
-                        let name = name.local_path();
+                        let name = name.stable_name();
                         let mut adapted = (**source_file).clone();
                         adapted.name = Path::new(&working_dir).join(name).into();
                         adapted.name_hash = {
diff --git a/src/librustc_span/lib.rs b/src/librustc_span/lib.rs
index 7a12d7da31f6c..94a5acc86107f 100644
--- a/src/librustc_span/lib.rs
+++ b/src/librustc_span/lib.rs
@@ -95,6 +95,7 @@ pub enum RealFileName {
 
 impl RealFileName {
     /// Returns the path suitable for reading from the file system on the local host.
+    /// Avoid embedding this in build artifacts; see `stable_name` for that.
     pub fn local_path(&self) -> &Path {
         match self {
             RealFileName::Named(p)
@@ -103,12 +104,24 @@ impl RealFileName {
     }
 
     /// Returns the path suitable for reading from the file system on the local host.
+    /// Avoid embedding this in build artifacts; see `stable_name` for that.
     pub fn into_local_path(self) -> PathBuf {
         match self {
             RealFileName::Named(p)
             | RealFileName::Devirtualized { local_path: p, virtual_name: _ } => p,
         }
     }
+
+    /// Returns the path suitable for embedding into build artifacts. Note that
+    /// a virtualized path will not correspond to a valid file system path; see
+    /// `local_path` for something that is more likely to return paths into the
+    /// local host file system.
+    pub fn stable_name(&self) -> &Path {
+        match self {
+            RealFileName::Named(p)
+            | RealFileName::Devirtualized { local_path: _, virtual_name: p } => &p,
+        }
+    }
 }
 
 /// Differentiates between real files and common virtual files.
diff --git a/src/librustc_span/source_map.rs b/src/librustc_span/source_map.rs
index e2ae32f6a1b34..54d3dc2c8676e 100644
--- a/src/librustc_span/source_map.rs
+++ b/src/librustc_span/source_map.rs
@@ -98,6 +98,8 @@ impl FileLoader for RealFileLoader {
 #[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug)]
 pub struct StableSourceFileId(u128);
 
+// FIXME: we need a more globally consistent approach to the problem solved by
+// StableSourceFileId, perhaps built atop source_file.name_hash.
 impl StableSourceFileId {
     pub fn new(source_file: &SourceFile) -> StableSourceFileId {
         StableSourceFileId::new_from_pieces(
@@ -114,7 +116,14 @@ impl StableSourceFileId {
     ) -> StableSourceFileId {
         let mut hasher = StableHasher::new();
 
-        name.hash(&mut hasher);
+        if let FileName::Real(real_name) = name {
+            // rust-lang/rust#70924: Use the stable (virtualized) name when
+            // available. (We do not want artifacts from transient file system
+            // paths for libstd to leak into our build artifacts.)
+            real_name.stable_name().hash(&mut hasher)
+        } else {
+            name.hash(&mut hasher);
+        }
         name_was_remapped.hash(&mut hasher);
         unmapped_path.hash(&mut hasher);