Include (potentially remapped) working dir in crate hash

Fixes #85019

A `SourceFile` created during compilation may have a relative
path (e.g. if rustc itself is invoked with a relative path).
When we write out crate metadata, we convert all relative paths
to absolute paths using the current working direction.

However, the working directory is not included in the crate hash.
This means that the crate metadata can change while the crate
hash remains the same. Among other problems, this can cause a
fingerprint mismatch ICE, since incremental compilation uses
the crate metadata hash to determine if a foreign query is green.

This commit moves the field holding the working directory from
`Session` to `Options`, including it as part of the crate hash.

compiler/rustc_session/src/config.rs

@@ -21,6 +21,7 @@ use rustc_feature::UnstableFeatures;
 use rustc_span::edition::{Edition, DEFAULT_EDITION, EDITION_NAME_LIST, LATEST_STABLE_EDITION};
 use rustc_span::source_map::{FileName, FilePathMapping};
 use rustc_span::symbol::{sym, Symbol};
+use rustc_span::RealFileName;
 use rustc_span::SourceFileHashAlgorithm;
 
 use rustc_errors::emitter::HumanReadableErrorType;
@@ -707,6 +708,7 @@ impl Default for Options {
             json_artifact_notifications: false,
             json_unused_externs: false,
             pretty: None,
+            working_dir: RealFileName::LocalPath(std::env::current_dir().unwrap()),
         }
     }
 }
@@ -2132,6 +2134,18 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         if candidate.join("library/std/src/lib.rs").is_file() { Some(candidate) } else { None }
     };
 
+    let working_dir = std::env::current_dir().unwrap_or_else(|e| {
+        early_error(error_format, &format!("Current directory is invalid: {}", e));
+    });
+
+    let (path, remapped) =
+        FilePathMapping::new(remap_path_prefix.clone()).map_prefix(working_dir.clone());
+    let working_dir = if remapped {
+        RealFileName::Remapped { local_path: Some(working_dir), virtual_name: path }
+    } else {
+        RealFileName::LocalPath(path)
+    };
+
     Options {
         crate_types,
         optimize: opt_level,
@@ -2167,6 +2181,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
         json_artifact_notifications,
         json_unused_externs,
         pretty,
+        working_dir,
     }
 }
 
@@ -2413,6 +2428,7 @@ crate mod dep_tracking {
     use crate::utils::{NativeLib, NativeLibKind};
     use rustc_feature::UnstableFeatures;
     use rustc_span::edition::Edition;
+    use rustc_span::RealFileName;
     use rustc_target::spec::{CodeModel, MergeFunctions, PanicStrategy, RelocModel};
     use rustc_target::spec::{RelroLevel, SanitizerSet, SplitDebuginfo, TargetTriple, TlsModel};
     use std::collections::hash_map::DefaultHasher;
@@ -2494,6 +2510,7 @@ crate mod dep_tracking {
         TrimmedDefPaths,
         Option<LdImpl>,
         OutputType,
+        RealFileName,
     );
 
     impl<T1, T2> DepTrackingHash for (T1, T2)