1 files changed, 39 insertions, 2 deletions
diff --git a/compiler/rustc_expand/src/base.rs b/compiler/rustc_expand/src/base.rs
index ae1b50a4176..2b30ec601a0 100644
--- a/compiler/rustc_expand/src/base.rs
+++ b/compiler/rustc_expand/src/base.rs
@@ -10,7 +10,7 @@ use rustc_ast::{self as ast, AstLike, Attribute, Item, NodeId, PatKind};
 use rustc_attr::{self as attr, Deprecation, Stability};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::sync::{self, Lrc};
-use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
+use rustc_errors::{Applicability, DiagnosticBuilder, ErrorGuaranteed, MultiSpan, PResult};
 use rustc_lint_defs::builtin::PROC_MACRO_BACK_COMPAT;
 use rustc_lint_defs::BuiltinLintDiagnostics;
 use rustc_parse::{self, nt_to_tokenstream, parser, MACRO_ARGUMENTS};
@@ -20,7 +20,7 @@ use rustc_span::edition::Edition;
 use rustc_span::hygiene::{AstPass, ExpnData, ExpnKind, LocalExpnId};
 use rustc_span::source_map::SourceMap;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
-use rustc_span::{Span, DUMMY_SP};
+use rustc_span::{FileName, Span, DUMMY_SP};
 use smallvec::{smallvec, SmallVec};
 
 use std::default::Default;
@@ -1136,6 +1136,43 @@ impl<'a> ExtCtxt<'a> {
     }
 }
 
+/// Resolves a `path` mentioned inside Rust code, returning an absolute path.
+///
+/// This unifies the logic used for resolving `include_X!`.
+pub fn resolve_path(
+    parse_sess: &ParseSess,
+    path: impl Into<PathBuf>,
+    span: Span,
+) -> PResult<'_, PathBuf> {
+    let path = path.into();
+
+    // Relative paths are resolved relative to the file in which they are found
+    // after macro expansion (that is, they are unhygienic).
+    if !path.is_absolute() {
+        let callsite = span.source_callsite();
+        let mut result = match parse_sess.source_map().span_to_filename(callsite) {
+            FileName::Real(name) => name
+                .into_local_path()
+                .expect("attempting to resolve a file path in an external file"),
+            FileName::DocTest(path, _) => path,
+            other => {
+                return Err(parse_sess.span_diagnostic.struct_span_err(
+                    span,
+                    &format!(
+                        "cannot resolve relative path in non-file source `{}`",
+                        parse_sess.source_map().filename_for_diagnostics(&other)
+                    ),
+                ));
+            }
+        };
+        result.pop();
+        result.push(path);
+        Ok(result)
+    } else {
+        Ok(path)
+    }
+}
+
 /// Extracts a string literal from the macro expanded version of `expr`,
 /// returning a diagnostic error of `err_msg` if `expr` is not a string literal.
 /// The returned bool indicates whether an applicable suggestion has already been