3 files changed, 41 insertions, 36 deletions

diff --git a/crates/rust-analyzer/src/config.rs b/crates/rust-analyzer/src/config.rs
index 7ddea22c8..3be335550 100644
--- a/crates/rust-analyzer/src/config.rs
+++ b/crates/rust-analyzer/src/config.rs
@@ -17,7 +17,7 @@ use ide_db::helpers::{
 };
 use lsp_types::{ClientCapabilities, MarkupKind};
 use project_model::{CargoConfig, ProjectJson, ProjectJsonData, ProjectManifest, RustcSource};
-use rustc_hash::FxHashSet;
+use rustc_hash::{FxHashMap, FxHashSet};
 use serde::{de::DeserializeOwned, Deserialize};
 use vfs::AbsPathBuf;
 
@@ -99,6 +99,9 @@ config_data! {
         diagnostics_enableExperimental: bool    = "true",
         /// List of rust-analyzer diagnostics to disable.
         diagnostics_disabled: FxHashSet<String> = "[]",
+        /// Map of path prefixes to be substituted when parsing diagnostic file paths.
+        /// This should be the reverse mapping of what is passed to `rustc` as `--remap-path-prefix`.
+        diagnostics_remapPathPrefixes: FxHashMap<String, String> = "{}",
         /// List of warnings that should be displayed with info severity.
         ///
         /// The warnings will be indicated by a blue squiggly underline in code
@@ -474,6 +477,7 @@ impl Config {
     }
     pub fn diagnostics_map(&self) -> DiagnosticsMapConfig {
         DiagnosticsMapConfig {
+            remap_path_prefixes: self.data.diagnostics_remapPathPrefixes.clone(),
             warnings_as_info: self.data.diagnostics_warningsAsInfo.clone(),
             warnings_as_hint: self.data.diagnostics_warningsAsHint.clone(),
         }
@@ -835,6 +839,9 @@ fn field_props(field: &str, ty: &str, doc: &[&str], default: &str) -> serde_json
             "items": { "type": "string" },
             "uniqueItems": true,
         },
+        "FxHashMap<String, String>" => set! {
+            "type": "object",
+        },
         "Option<usize>" => set! {
             "type": ["null", "integer"],
             "minimum": 0,
diff --git a/crates/rust-analyzer/src/diagnostics.rs b/crates/rust-analyzer/src/diagnostics.rs
index f01548c50..776d21778 100644
--- a/crates/rust-analyzer/src/diagnostics.rs
+++ b/crates/rust-analyzer/src/diagnostics.rs
@@ -12,6 +12,7 @@ pub(crate) type CheckFixes = Arc<FxHashMap<FileId, Vec<Fix>>>;
 
 #[derive(Debug, Default, Clone)]
 pub struct DiagnosticsMapConfig {
+    pub remap_path_prefixes: FxHashMap<String, String>,
     pub warnings_as_info: Vec<String>,
     pub warnings_as_hint: Vec<String>,
 }
diff --git a/crates/rust-analyzer/src/diagnostics/to_proto.rs b/crates/rust-analyzer/src/diagnostics/to_proto.rs
index 8b01a7e5d..08303a781 100644
--- a/crates/rust-analyzer/src/diagnostics/to_proto.rs
+++ b/crates/rust-analyzer/src/diagnostics/to_proto.rs
@@ -44,8 +44,12 @@ fn is_dummy_macro_file(file_name: &str) -> bool {
 }
 
 /// Converts a Rust span to a LSP location
-fn location(workspace_root: &Path, span: &DiagnosticSpan) -> lsp_types::Location {
-    let file_name = resolve_path(workspace_root, &span.file_name);
+fn location(
+    config: &DiagnosticsMapConfig,
+    workspace_root: &Path,
+    span: &DiagnosticSpan,
+) -> lsp_types::Location {
+    let file_name = resolve_path(config, workspace_root, &span.file_name);
     let uri = url_from_abs_path(&file_name);
 
     // FIXME: this doesn't handle UTF16 offsets correctly
@@ -61,54 +65,46 @@ fn location(workspace_root: &Path, span: &DiagnosticSpan) -> lsp_types::Location
 ///
 /// This takes locations pointing into the standard library, or generally outside the current
 /// workspace into account and tries to avoid those, in case macros are involved.
-fn primary_location(workspace_root: &Path, span: &DiagnosticSpan) -> lsp_types::Location {
+fn primary_location(
+    config: &DiagnosticsMapConfig,
+    workspace_root: &Path,
+    span: &DiagnosticSpan,
+) -> lsp_types::Location {
     let span_stack = std::iter::successors(Some(span), |span| Some(&span.expansion.as_ref()?.span));
     for span in span_stack.clone() {
-        let abs_path = resolve_path(workspace_root, &span.file_name);
+        let abs_path = resolve_path(config, workspace_root, &span.file_name);
         if !is_dummy_macro_file(&span.file_name) && abs_path.starts_with(workspace_root) {
-            return location(workspace_root, span);
+            return location(config, workspace_root, span);
         }
     }
 
     // Fall back to the outermost macro invocation if no suitable span comes up.
     let last_span = span_stack.last().unwrap();
-    location(workspace_root, last_span)
+    location(config, workspace_root, last_span)
 }
 
 /// Converts a secondary Rust span to a LSP related information
 ///
 /// If the span is unlabelled this will return `None`.
 fn diagnostic_related_information(
+    config: &DiagnosticsMapConfig,
     workspace_root: &Path,
     span: &DiagnosticSpan,
 ) -> Option<lsp_types::DiagnosticRelatedInformation> {
     let message = span.label.clone()?;
-    let location = location(workspace_root, span);
+    let location = location(config, workspace_root, span);
     Some(lsp_types::DiagnosticRelatedInformation { location, message })
 }
 
-/// Resolves paths mimicking VSCode's behavior when `file_name` starts
-/// with the root directory component, which does not discard the base
-/// path.  If this relative path exists, use it, otherwise fall back
-/// to the existing Rust behavior of path joining.
-fn resolve_path(workspace_root: &Path, file_name: &str) -> PathBuf {
-    let file_name = Path::new(file_name);
-
-    // Test path with VSCode's path join behavior.
-    let vscode_path = {
-        let mut result = PathBuf::from(workspace_root);
-        result.extend(file_name.components().skip_while(|component| match component {
-            std::path::Component::RootDir => true,
-            _ => false,
-        }));
-        result
-    };
-    if vscode_path.exists() {
-        return vscode_path;
+/// Resolves paths applying any matching path prefix remappings, and then
+/// joining the path to the workspace root.
+fn resolve_path(config: &DiagnosticsMapConfig, workspace_root: &Path, file_name: &str) -> PathBuf {
+    match config.remap_path_prefixes.iter().find(|(from, _)| file_name.starts_with(*from)) {
+        Some((from, to)) => {
+            workspace_root.join(format!("{}{}", to, file_name.strip_prefix(from).unwrap()))
+        }
+        None => workspace_root.join(file_name),
     }
-
-    // Default to Rust's path join behavior.
-    workspace_root.join(file_name)
 }
 
 struct SubDiagnostic {
@@ -122,6 +118,7 @@ enum MappedRustChildDiagnostic {
 }
 
 fn map_rust_child_diagnostic(
+    config: &DiagnosticsMapConfig,
     workspace_root: &Path,
     rd: &flycheck::Diagnostic,
 ) -> MappedRustChildDiagnostic {
@@ -135,7 +132,7 @@ fn map_rust_child_diagnostic(
     let mut edit_map: HashMap<lsp_types::Url, Vec<lsp_types::TextEdit>> = HashMap::new();
     for &span in &spans {
         if let Some(suggested_replacement) = &span.suggested_replacement {
-            let location = location(workspace_root, span);
+            let location = location(config, workspace_root, span);
             let edit = lsp_types::TextEdit::new(location.range, suggested_replacement.clone());
             edit_map.entry(location.uri).or_default().push(edit);
         }
@@ -144,7 +141,7 @@ fn map_rust_child_diagnostic(
     if edit_map.is_empty() {
         MappedRustChildDiagnostic::SubDiagnostic(SubDiagnostic {
             related: lsp_types::DiagnosticRelatedInformation {
-                location: location(workspace_root, spans[0]),
+                location: location(config, workspace_root, spans[0]),
                 message: rd.message.clone(),
             },
             suggested_fix: None,
@@ -152,7 +149,7 @@ fn map_rust_child_diagnostic(
     } else {
         MappedRustChildDiagnostic::SubDiagnostic(SubDiagnostic {
             related: lsp_types::DiagnosticRelatedInformation {
-                location: location(workspace_root, spans[0]),
+                location: location(config, workspace_root, spans[0]),
                 message: rd.message.clone(),
             },
             suggested_fix: Some(lsp_ext::CodeAction {
@@ -217,7 +214,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
     let mut tags = Vec::new();
 
     for secondary_span in rd.spans.iter().filter(|s| !s.is_primary) {
-        let related = diagnostic_related_information(workspace_root, secondary_span);
+        let related = diagnostic_related_information(config, workspace_root, secondary_span);
         if let Some(related) = related {
             subdiagnostics.push(SubDiagnostic { related, suggested_fix: None });
         }
@@ -225,7 +222,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
 
     let mut message = rd.message.clone();
     for child in &rd.children {
-        let child = map_rust_child_diagnostic(workspace_root, &child);
+        let child = map_rust_child_diagnostic(config, workspace_root, &child);
         match child {
             MappedRustChildDiagnostic::SubDiagnostic(sub) => {
                 subdiagnostics.push(sub);
@@ -269,7 +266,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
     primary_spans
         .iter()
         .flat_map(|primary_span| {
-            let primary_location = primary_location(workspace_root, &primary_span);
+            let primary_location = primary_location(config, workspace_root, &primary_span);
 
             let mut message = message.clone();
             if needs_primary_span_label {
@@ -299,7 +296,7 @@ pub(crate) fn map_rust_diagnostic_to_lsp(
                 // generated that code.
                 let is_in_macro_call = i != 0;
 
-                let secondary_location = location(workspace_root, &span);
+                let secondary_location = location(config, workspace_root, &span);
                 if secondary_location == primary_location {
                     continue;
                 }