7 files changed, 150 insertions, 34 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 52d72c3c5..800101c91 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -2053,7 +2053,7 @@ impl Type {
         name: Option<&Name>,
         mut callback: impl FnMut(&Ty, AssocItem) -> Option<T>,
     ) -> Option<T> {
-        let canonical = hir_ty::replace_errors_with_variables(self.ty.clone());
+        let canonical = hir_ty::replace_errors_with_variables(&self.ty);
 
         let env = self.env.clone();
         let krate = krate.id;
@@ -2222,7 +2222,7 @@ impl Type {
     }
 
     pub fn could_unify_with(&self, db: &dyn HirDatabase, other: &Type) -> bool {
-        let tys = hir_ty::replace_errors_with_variables((self.ty.clone(), other.ty.clone()));
+        let tys = hir_ty::replace_errors_with_variables(&(self.ty.clone(), other.ty.clone()));
         could_unify(db, self.env.clone(), &tys)
     }
 }
diff --git a/crates/hir/src/semantics.rs b/crates/hir/src/semantics.rs
index 38bd376bc..1b5064b5a 100644
--- a/crates/hir/src/semantics.rs
+++ b/crates/hir/src/semantics.rs
@@ -505,9 +505,10 @@ impl<'db> SemanticsImpl<'db> {
     }
 
     fn resolve_method_call_as_callable(&self, call: &ast::MethodCallExpr) -> Option<Callable> {
-        // FIXME: this erases Substs
+        // FIXME: this erases Substs, we should instead record the correct
+        // substitution during inference and use that
         let func = self.resolve_method_call(call)?;
-        let (ty, _) = self.db.value_ty(func.into()).into_value_and_skipped_binders();
+        let ty = hir_ty::TyBuilder::value_ty(self.db, func.into()).fill_with_unknown().build();
         let resolver = self.analyze(call.syntax()).resolver;
         let ty = Type::new_with_resolver(self.db, &resolver, ty)?;
         let mut res = ty.as_callable(self.db)?;
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index 72093d75a..ef021978a 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -43,7 +43,6 @@ use hir_def::{
     type_ref::{ConstScalar, Rawness},
     TypeParamId,
 };
-use stdx::always;
 
 use crate::{db::HirDatabase, utils::generics};
 
@@ -329,14 +328,17 @@ pub(crate) fn fold_tys<T: HasInterner<Interner = Interner> + Fold<Interner>>(
     t.fold_with(&mut TyFolder(f), binders).expect("fold failed unexpectedly")
 }
 
-pub fn replace_errors_with_variables<T>(t: T) -> Canonical<T::Result>
+/// 'Canonicalizes' the `t` by replacing any errors with new variables. Also
+/// ensures there are no unbound variables or inference variables anywhere in
+/// the `t`.
+pub fn replace_errors_with_variables<T>(t: &T) -> Canonical<T::Result>
 where
-    T: HasInterner<Interner = Interner> + Fold<Interner>,
+    T: HasInterner<Interner = Interner> + Fold<Interner> + Clone,
     T::Result: HasInterner<Interner = Interner>,
 {
     use chalk_ir::{
         fold::{Folder, SuperFold},
-        Fallible,
+        Fallible, NoSolution,
     };
     struct ErrorReplacer {
         vars: usize,
@@ -363,18 +365,88 @@ where
 
         fn fold_inference_ty(
             &mut self,
-            var: InferenceVar,
-            kind: TyVariableKind,
+            _var: InferenceVar,
+            _kind: TyVariableKind,
+            _outer_binder: DebruijnIndex,
+        ) -> Fallible<Ty> {
+            if cfg!(debug_assertions) {
+                // we don't want to just panic here, because then the error message
+                // won't contain the whole thing, which would not be very helpful
+                Err(NoSolution)
+            } else {
+                Ok(TyKind::Error.intern(&Interner))
+            }
+        }
+
+        fn fold_free_var_ty(
+            &mut self,
+            _bound_var: BoundVar,
             _outer_binder: DebruijnIndex,
         ) -> Fallible<Ty> {
-            always!(false);
-            Ok(TyKind::InferenceVar(var, kind).intern(&Interner))
+            if cfg!(debug_assertions) {
+                // we don't want to just panic here, because then the error message
+                // won't contain the whole thing, which would not be very helpful
+                Err(NoSolution)
+            } else {
+                Ok(TyKind::Error.intern(&Interner))
+            }
+        }
+
+        fn fold_inference_const(
+            &mut self,
+            _ty: Ty,
+            _var: InferenceVar,
+            _outer_binder: DebruijnIndex,
+        ) -> Fallible<Const> {
+            if cfg!(debug_assertions) {
+                Err(NoSolution)
+            } else {
+                Ok(dummy_usize_const())
+            }
+        }
+
+        fn fold_free_var_const(
+            &mut self,
+            _ty: Ty,
+            _bound_var: BoundVar,
+            _outer_binder: DebruijnIndex,
+        ) -> Fallible<Const> {
+            if cfg!(debug_assertions) {
+                Err(NoSolution)
+            } else {
+                Ok(dummy_usize_const())
+            }
+        }
+
+        fn fold_inference_lifetime(
+            &mut self,
+            _var: InferenceVar,
+            _outer_binder: DebruijnIndex,
+        ) -> Fallible<Lifetime> {
+            if cfg!(debug_assertions) {
+                Err(NoSolution)
+            } else {
+                Ok(static_lifetime())
+            }
+        }
+
+        fn fold_free_var_lifetime(
+            &mut self,
+            _bound_var: BoundVar,
+            _outer_binder: DebruijnIndex,
+        ) -> Fallible<Lifetime> {
+            if cfg!(debug_assertions) {
+                Err(NoSolution)
+            } else {
+                Ok(static_lifetime())
+            }
         }
     }
     let mut error_replacer = ErrorReplacer { vars: 0 };
-    let value = t
-        .fold_with(&mut error_replacer, DebruijnIndex::INNERMOST)
-        .expect("fold failed unexpectedly");
+    let value = match t.clone().fold_with(&mut error_replacer, DebruijnIndex::INNERMOST) {
+        Ok(t) => t,
+        Err(_) => panic!("Encountered unbound or inference vars in {:?}", t),
+    };
     let kinds = (0..error_replacer.vars).map(|_| {
         chalk_ir::CanonicalVarKind::new(
             chalk_ir::VariableKind::Ty(TyVariableKind::General),
diff --git a/crates/ide_completion/src/completions/dot.rs b/crates/ide_completion/src/completions/dot.rs
index 7e4efe589..fd9738743 100644
--- a/crates/ide_completion/src/completions/dot.rs
+++ b/crates/ide_completion/src/completions/dot.rs
@@ -454,4 +454,34 @@ mod foo {
             "#]],
         );
     }
+
+    #[test]
+    fn issue_8931() {
+        check(
+            r#"
+#[lang = "fn_once"]
+trait FnOnce<Args> {
+    type Output;
+}
+struct S;
+
+struct Foo;
+impl Foo {
+    fn foo(&self) -> &[u8] { loop {} }
+}
+
+impl S {
+    fn indented(&mut self, f: impl FnOnce(&mut Self)) {
+    }
+
+    fn f(&mut self, v: Foo) {
+        self.indented(|this| v.$0)
+    }
+}
+        "#,
+            expect![[r#"
+                me foo() fn(&self) -> &[u8]
+            "#]],
+        );
+    }
 }
diff --git a/editors/code/src/config.ts b/editors/code/src/config.ts
index e858f80bc..fbb7a556a 100644
--- a/editors/code/src/config.ts
+++ b/editors/code/src/config.ts
@@ -4,7 +4,7 @@ import { log } from "./util";
 
 export type UpdatesChannel = "stable" | "nightly";
 
-export const NIGHTLY_TAG = "nightly";
+const NIGHTLY_TAG = "nightly";
 
 export type RunnableEnvCfg = undefined | Record<string, string> | { mask?: string; env: Record<string, string> }[];
 
@@ -34,7 +34,7 @@ export class Config {
     readonly globalStoragePath: string;
 
     constructor(ctx: vscode.ExtensionContext) {
-        this.globalStoragePath = ctx.globalStoragePath;
+        this.globalStoragePath = ctx.globalStorageUri.path;
         vscode.workspace.onDidChangeConfiguration(this.onDidChangeConfiguration, this, ctx.subscriptions);
         this.refreshLogging();
     }
@@ -170,4 +170,8 @@ export class Config {
             gotoTypeDef: this.get<boolean>("hoverActions.gotoTypeDef"),
         };
     }
+
+    get currentExtensionIsNightly() {
+        return this.package.releaseTag === NIGHTLY_TAG;
+    }
 }
diff --git a/editors/code/src/main.ts b/editors/code/src/main.ts
index 92c797d47..aaedc2431 100644
--- a/editors/code/src/main.ts
+++ b/editors/code/src/main.ts
@@ -6,7 +6,7 @@ import { promises as fs, PathLike } from "fs";
 import * as commands from './commands';
 import { activateInlayHints } from './inlay_hints';
 import { Ctx } from './ctx';
-import { Config, NIGHTLY_TAG } from './config';
+import { Config } from './config';
 import { log, assert, isValidExecutable } from './util';
 import { PersistentState } from './persistent_state';
 import { fetchRelease, download } from './net';
@@ -156,16 +156,18 @@ export async function deactivate() {
 async function bootstrap(config: Config, state: PersistentState): Promise<string> {
     await fs.mkdir(config.globalStoragePath, { recursive: true });
 
+    if (!config.currentExtensionIsNightly) {
+        await state.updateNightlyReleaseId(undefined);
+    }
     await bootstrapExtension(config, state);
     const path = await bootstrapServer(config, state);
-
     return path;
 }
 
 async function bootstrapExtension(config: Config, state: PersistentState): Promise<void> {
     if (config.package.releaseTag === null) return;
     if (config.channel === "stable") {
-        if (config.package.releaseTag === NIGHTLY_TAG) {
+        if (config.currentExtensionIsNightly) {
             void vscode.window.showWarningMessage(
                 `You are running a nightly version of rust-analyzer extension. ` +
                 `To switch to stable, uninstall the extension and re-install it from the marketplace`
@@ -176,27 +178,34 @@ async function bootstrapExtension(config: Config, state: PersistentState): Promi
     if (serverPath(config)) return;
 
     const now = Date.now();
-    if (config.package.releaseTag === NIGHTLY_TAG) {
+    const isInitialNightlyDownload = state.nightlyReleaseId === undefined;
+    if (config.currentExtensionIsNightly) {
         // Check if we should poll github api for the new nightly version
         // if we haven't done it during the past hour
         const lastCheck = state.lastCheck;
 
         const anHour = 60 * 60 * 1000;
-        const shouldCheckForNewNightly = state.releaseId === undefined || (now - (lastCheck ?? 0)) > anHour;
+        const shouldCheckForNewNightly = isInitialNightlyDownload || (now - (lastCheck ?? 0)) > anHour;
 
         if (!shouldCheckForNewNightly) return;
     }
 
-    const release = await downloadWithRetryDialog(state, async () => {
+    const latestNightlyRelease = await downloadWithRetryDialog(state, async () => {
         return await fetchRelease("nightly", state.githubToken, config.httpProxy);
     }).catch(async (e) => {
         log.error(e);
-        if (state.releaseId === undefined) { // Show error only for the initial download
-            await vscode.window.showErrorMessage(`Failed to download rust-analyzer nightly ${e}`);
+        if (isInitialNightlyDownload) {
+            await vscode.window.showErrorMessage(`Failed to download rust-analyzer nightly: ${e}`);
         }
-        return undefined;
+        return;
     });
-    if (release === undefined || release.id === state.releaseId) return;
+    if (latestNightlyRelease === undefined) {
+        if (isInitialNightlyDownload) {
+            await vscode.window.showErrorMessage("Failed to download rust-analyzer nightly: empty release contents returned");
+        }
+        return;
+    }
+    if (config.currentExtensionIsNightly && latestNightlyRelease.id === state.nightlyReleaseId) return;
 
     const userResponse = await vscode.window.showInformationMessage(
         "New version of rust-analyzer (nightly) is available (requires reload).",
@@ -204,8 +213,8 @@ async function bootstrapExtension(config: Config, state: PersistentState): Promi
     );
     if (userResponse !== "Update") return;
 
-    const artifact = release.assets.find(artifact => artifact.name === "rust-analyzer.vsix");
-    assert(!!artifact, `Bad release: ${JSON.stringify(release)}`);
+    const artifact = latestNightlyRelease.assets.find(artifact => artifact.name === "rust-analyzer.vsix");
+    assert(!!artifact, `Bad release: ${JSON.stringify(latestNightlyRelease)}`);
 
     const dest = path.join(config.globalStoragePath, "rust-analyzer.vsix");
 
@@ -221,7 +230,7 @@ async function bootstrapExtension(config: Config, state: PersistentState): Promi
     await vscode.commands.executeCommand("workbench.extensions.installExtension", vscode.Uri.file(dest));
     await fs.unlink(dest);
 
-    await state.updateReleaseId(release.id);
+    await state.updateNightlyReleaseId(latestNightlyRelease.id);
     await state.updateLastCheck(now);
     await vscode.commands.executeCommand("workbench.action.reloadWindow");
 }
diff --git a/editors/code/src/persistent_state.ts b/editors/code/src/persistent_state.ts
index afb652589..dd2aeecca 100644
--- a/editors/code/src/persistent_state.ts
+++ b/editors/code/src/persistent_state.ts
@@ -3,8 +3,8 @@ import { log } from './util';
 
 export class PersistentState {
     constructor(private readonly globalState: vscode.Memento) {
-        const { lastCheck, releaseId, serverVersion } = this;
-        log.info("PersistentState:", { lastCheck, releaseId, serverVersion });
+        const { lastCheck, nightlyReleaseId, serverVersion } = this;
+        log.info("PersistentState:", { lastCheck, nightlyReleaseId, serverVersion });
     }
 
     /**
@@ -21,10 +21,10 @@ export class PersistentState {
      * Release id of the *nightly* extension.
      * Used to check if we should update.
      */
-    get releaseId(): number | undefined {
+    get nightlyReleaseId(): number | undefined {
         return this.globalState.get("releaseId");
     }
-    async updateReleaseId(value: number) {
+    async updateNightlyReleaseId(value: number | undefined) {
         await this.globalState.update("releaseId", value);
     }