rustdoc: Add support for --remap-path-prefix

Adds --remap-path-prefix as an unstable option. This is implemented to
mimic the behavior of rustc's --remap-path-prefix but with minor
adjustments.

This flag similarly takes in two paths, a prefix to replace and a
replacement string.

src/librustdoc/config.rs

@@ -125,6 +125,8 @@ pub(crate) struct Options {
     pub(crate) enable_per_target_ignores: bool,
     /// Do not run doctests, compile them if should_test is active.
     pub(crate) no_run: bool,
+    /// What sources are being mapped.
+    pub(crate) remap_path_prefix: Vec<(PathBuf, PathBuf)>,
 
     /// The path to a rustc-like binary to build tests with. If not set, we
     /// default to loading from `$sysroot/bin/rustc`.
@@ -208,6 +210,7 @@ impl fmt::Debug for Options {
             .field("run_check", &self.run_check)
             .field("no_run", &self.no_run)
             .field("test_builder_wrappers", &self.test_builder_wrappers)
+            .field("remap-file-prefix", &self.remap_path_prefix)
             .field("nocapture", &self.nocapture)
             .field("scrape_examples_options", &self.scrape_examples_options)
             .field("unstable_features", &self.unstable_features)
@@ -355,6 +358,13 @@ impl Options {
         let unstable_opts = UnstableOptions::build(early_dcx, matches);
         let force_unstable_if_unmarked = unstable_opts.force_unstable_if_unmarked;
 
+        let remap_path_prefix = match parse_remap_path_prefix(&matches) {
+            Ok(prefix_mappings) => prefix_mappings,
+            Err(err) => {
+                early_dcx.early_fatal(err);
+            }
+        };
+
         let dcx = new_dcx(error_format, None, diagnostic_width, &unstable_opts);
 
         // check for deprecated options
@@ -734,6 +744,7 @@ impl Options {
             run_check,
             no_run,
             test_builder_wrappers,
+            remap_path_prefix,
             nocapture,
             crate_name,
             output_format,
@@ -781,6 +792,21 @@ impl Options {
     }
 }
 
+fn parse_remap_path_prefix(
+    matches: &getopts::Matches,
+) -> Result<Vec<(PathBuf, PathBuf)>, &'static str> {
+    matches
+        .opt_strs("remap-path-prefix")
+        .into_iter()
+        .map(|remap| {
+            remap
+                .rsplit_once('=')
+                .ok_or("--remap-path-prefix must contain '=' between FROM and TO")
+                .map(|(from, to)| (PathBuf::from(from), PathBuf::from(to)))
+        })
+        .collect()
+}
+
 /// Prints deprecation warnings for deprecated options
 fn check_deprecated_options(matches: &getopts::Matches, dcx: &rustc_errors::DiagCtxt) {
     let deprecated_flags = [];

src/librustdoc/doctest.rs

@@ -16,7 +16,7 @@ use rustc_session::config::{self, CrateType, ErrorOutputType};
 use rustc_session::parse::ParseSess;
 use rustc_session::{lint, Session};
 use rustc_span::edition::Edition;
-use rustc_span::source_map::SourceMap;
+use rustc_span::source_map::{FilePathMapping, SourceMap};
 use rustc_span::symbol::sym;
 use rustc_span::{BytePos, FileName, Pos, Span, DUMMY_SP};
 use rustc_target::spec::{Target, TargetTriple};
@@ -86,6 +86,7 @@ pub(crate) fn run(options: RustdocOptions) -> Result<(), ErrorGuaranteed> {
         edition: options.edition,
         target_triple: options.target.clone(),
         crate_name: options.crate_name.clone(),
+        remap_path_prefix: options.remap_path_prefix.clone(),
         ..config::Options::default()
     };
 
@@ -577,7 +578,6 @@ pub(crate) fn make_test(
             use rustc_errors::emitter::{Emitter, HumanEmitter};
             use rustc_errors::DiagCtxt;
             use rustc_parse::parser::ForceCollect;
-            use rustc_span::source_map::FilePathMapping;
 
             let filename = FileName::anon_source_code(s);
             let source = crates + everything_else;
@@ -768,7 +768,6 @@ fn check_if_attr_is_complete(source: &str, edition: Edition) -> bool {
         rustc_span::create_session_if_not_set_then(edition, |_| {
             use rustc_errors::emitter::HumanEmitter;
             use rustc_errors::DiagCtxt;
-            use rustc_span::source_map::FilePathMapping;
 
             let filename = FileName::anon_source_code(source);
             // Any errors in parsing should also appear when the doctest is compiled for real, so just
@@ -976,7 +975,7 @@ impl Collector {
         if !item_path.is_empty() {
             item_path.push(' ');
         }
-        format!("{} - {item_path}(line {line})", filename.prefer_local())
+        format!("{} - {item_path}(line {line})", filename.prefer_remapped_unconditionaly())
     }
 
     pub(crate) fn set_position(&mut self, position: Span) {
@@ -986,11 +985,15 @@ impl Collector {
     fn get_filename(&self) -> FileName {
         if let Some(ref source_map) = self.source_map {
             let filename = source_map.span_to_filename(self.position);
-            if let FileName::Real(ref filename) = filename
-                && let Ok(cur_dir) = env::current_dir()
-                && let Some(local_path) = filename.local_path()
-                && let Ok(path) = local_path.strip_prefix(&cur_dir)
-            {
+            if let FileName::Real(ref filename) = filename {
+                let path = filename.remapped_path_if_available();
+
+                // Strip the cwd prefix from the path. This will likely exist if
+                // the path was not remapped.
+                let path = env::current_dir()
+                    .map(|cur_dir| path.strip_prefix(&cur_dir).unwrap_or(path))
+                    .unwrap_or(path);
+
                 return path.to_owned().into();
             }
             filename
@@ -1021,20 +1024,13 @@ impl Tester for Collector {
         }
 
         let path = match &filename {
-            FileName::Real(path) => {
-                if let Some(local_path) = path.local_path() {
-                    local_path.to_path_buf()
-                } else {
-                    // Somehow we got the filename from the metadata of another crate, should never happen
-                    unreachable!("doctest from a different crate");
-                }
-            }
+            FileName::Real(path) => path.remapped_path_if_available().to_path_buf(),
             _ => PathBuf::from(r"doctest.rs"),
         };
 
         // For example `module/file.rs` would become `module_file_rs`
         let file = filename
-            .prefer_local()
+            .prefer_remapped_unconditionaly()
             .to_string_lossy()
             .chars()
             .map(|c| if c.is_ascii_alphanumeric() { c } else { '_' })

src/librustdoc/lib.rs

@@ -557,6 +557,14 @@ fn opts() -> Vec<RustcOptGroup> {
         unstable("no-run", |o| {
             o.optflagmulti("", "no-run", "Compile doctests without running them")
         }),
+        unstable("remap-path-prefix", |o| {
+            o.optmulti(
+                "",
+                "remap-path-prefix",
+                "Remap source names in compiler messages",
+                "FROM=TO",
+            )
+        }),
         unstable("show-type-layout", |o| {
             o.optflagmulti("", "show-type-layout", "Include the memory layout of types in the docs")
         }),

tests/run-make/issue-88756-default-output/output-default.stdout

@@ -157,6 +157,8 @@ Options:
                         Comma separated list of types of output for rustdoc to
                         emit
         --no-run        Compile doctests without running them
+        --remap-path-prefix FROM=TO
+                        Remap source names in compiler messages
         --show-type-layout 
                         Include the memory layout of types in the docs
         --nocapture     Don't capture stdout and stderr of tests

tests/rustdoc-ui/remap-path-prefix-failed-doctest-output.rs

@@ -0,0 +1,13 @@
+// FIXME: if/when the output of the test harness can be tested on its own, this test should be
+// adapted to use that, and that normalize line can go away
+
+//@ compile-flags:--test -Z unstable-options --remap-path-prefix={{src-base}}=remapped_path --test-args --test-threads=1
+//@ rustc-env:RUST_BACKTRACE=0
+//@ normalize-stdout-test "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ failure-status: 101
+
+// doctest fails at runtime
+/// ```
+/// panic!("oh no");
+/// ```
+pub struct SomeStruct;

tests/rustdoc-ui/remap-path-prefix-failed-doctest-output.stdout

@@ -0,0 +1,21 @@
+
+running 1 test
+test remapped_path/remap-path-prefix-failed-doctest-output.rs - SomeStruct (line 10) ... FAILED
+
+failures:
+
+---- remapped_path/remap-path-prefix-failed-doctest-output.rs - SomeStruct (line 10) stdout ----
+Test executable failed (exit status: 101).
+
+stderr:
+thread 'main' panicked at remapped_path/remap-path-prefix-failed-doctest-output.rs:3:1:
+oh no
+note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+
+
+
+failures:
+    remapped_path/remap-path-prefix-failed-doctest-output.rs - SomeStruct (line 10)
+
+test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+

tests/rustdoc-ui/remap-path-prefix-invalid-doctest.rs

@@ -0,0 +1,13 @@
+// FIXME: if/when the output of the test harness can be tested on its own, this test should be
+// adapted to use that, and that normalize line can go away
+
+//@ compile-flags:--test -Z unstable-options --remap-path-prefix={{src-base}}=remapped_path --test-args --test-threads=1
+//@ rustc-env:RUST_BACKTRACE=0
+//@ normalize-stdout-test "finished in \d+\.\d+s" -> "finished in $$TIME"
+//@ failure-status: 101
+
+// doctest fails to compile
+/// ```
+/// this is not real code
+/// ```
+pub struct SomeStruct;

tests/rustdoc-ui/remap-path-prefix-invalid-doctest.stdout

@@ -0,0 +1,22 @@
+
+running 1 test
+test remapped_path/remap-path-prefix-invalid-doctest.rs - SomeStruct (line 10) ... FAILED
+
+failures:
+
+---- remapped_path/remap-path-prefix-invalid-doctest.rs - SomeStruct (line 10) stdout ----
+error: expected one of `!`, `.`, `::`, `;`, `?`, `{`, `}`, or an operator, found `is`
+  --> remapped_path/remap-path-prefix-invalid-doctest.rs:11:6
+   |
+LL | this is not real code
+   |      ^^ expected one of 8 possible tokens
+
+error: aborting due to 1 previous error
+
+Couldn't compile the test.
+
+failures:
+    remapped_path/remap-path-prefix-invalid-doctest.rs - SomeStruct (line 10)
+
+test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+

tests/rustdoc-ui/remap-path-prefix-passed-doctest-output.rs

@@ -0,0 +1,14 @@
+//@ check-pass
+//@ check-run-results
+
+// FIXME: if/when the output of the test harness can be tested on its own, this test should be
+// adapted to use that, and that normalize line can go away
+
+//@ compile-flags:--test -Z unstable-options --remap-path-prefix={{src-base}}=remapped_path --test-args --test-threads=1
+//@ normalize-stdout-test "finished in \d+\.\d+s" -> "finished in $$TIME"
+
+// doctest passes at runtime
+/// ```
+/// assert!(true);
+/// ```
+pub struct SomeStruct;

tests/rustdoc-ui/remap-path-prefix-passed-doctest-output.stdout

@@ -0,0 +1,6 @@
+
+running 1 test
+test remapped_path/remap-path-prefix-passed-doctest-output.rs - SomeStruct (line 11) ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in $TIME
+