Add rustc lint, warning when iterating over hashmaps

compiler/rustc_ast_lowering/src/lib.rs

@@ -34,6 +34,7 @@
 #![feature(box_patterns)]
 #![feature(iter_zip)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::token::{self, Token};

compiler/rustc_ast_passes/src/lib.rs

@@ -7,6 +7,7 @@
 #![feature(iter_is_partitioned)]
 #![feature(box_patterns)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 pub mod ast_validation;
 pub mod feature_gate;

compiler/rustc_borrowck/src/lib.rs

@@ -12,6 +12,7 @@
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate rustc_middle;

compiler/rustc_builtin_macros/src/lib.rs

@@ -11,6 +11,7 @@
 #![feature(proc_macro_internals)]
 #![feature(proc_macro_quote)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 extern crate proc_macro;
 

compiler/rustc_codegen_llvm/src/lib.rs

@@ -13,6 +13,7 @@
 #![feature(iter_zip)]
 #![feature(nll)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 use back::write::{create_informational_target_machine, create_target_machine};
 

compiler/rustc_codegen_ssa/src/lib.rs

@@ -7,6 +7,7 @@
 #![feature(nll)]
 #![feature(associated_type_bounds)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 //! This crate contains codegen code that is used by all codegen backends (LLVM and others).
 //! The backend-agnostic functions of this crate use functions defined in various traits that

compiler/rustc_const_eval/src/lib.rs

@@ -23,6 +23,7 @@ Rust MIR: a lowered representation of Rust.
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate tracing;

compiler/rustc_data_structures/src/lib.rs

@@ -28,6 +28,7 @@
 #![feature(thread_id_value)]
 #![allow(rustc::default_hash_types)]
 #![deny(unaligned_references)]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate tracing;

compiler/rustc_driver/src/lib.rs

@@ -8,6 +8,7 @@
 #![feature(nll)]
 #![feature(once_cell)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate tracing;
@@ -846,7 +847,7 @@ Available lint options:
     let builtin = sort_lints(sess, builtin);
 
     let (plugin_groups, builtin_groups): (Vec<_>, _) =
-        lint_store.get_lint_groups().iter().cloned().partition(|&(.., p)| p);
+        lint_store.get_lint_groups().partition(|&(.., p)| p);
     let plugin_groups = sort_lint_groups(plugin_groups);
     let builtin_groups = sort_lint_groups(builtin_groups);
 

compiler/rustc_errors/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(format_args_capture)]
 #![feature(iter_zip)]
 #![feature(nll)]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate rustc_macros;

compiler/rustc_expand/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(proc_macro_span)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate rustc_macros;

compiler/rustc_feature/src/builtin_attrs.rs

@@ -460,6 +460,9 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
     // Prevents field reads in the marked trait or method to be considered
     // during dead code analysis.
     rustc_attr!(rustc_trivial_field_reads, Normal, template!(Word), INTERNAL_UNSTABLE),
+    // Used by the `rustc::potential_query_instability` lint to warn methods which
+    // might not be stable during incremental compilation.
+    rustc_attr!(rustc_lint_query_instability, Normal, template!(Word), INTERNAL_UNSTABLE),
 
     // ==========================================================================
     // Internal attributes, Const related:

compiler/rustc_incremental/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate rustc_middle;

compiler/rustc_infer/src/lib.rs

@@ -23,6 +23,7 @@
 #![feature(min_specialization)]
 #![feature(label_break_value)]
 #![recursion_limit = "512"] // For rustdoc
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate rustc_macros;

compiler/rustc_interface/src/lib.rs

@@ -5,6 +5,7 @@
 #![feature(nll)]
 #![feature(once_cell)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 mod callbacks;
 pub mod interface;

compiler/rustc_lint/src/context.rs

@@ -144,7 +144,11 @@ impl LintStore {
         &self.lints
     }
 
-    pub fn get_lint_groups<'t>(&'t self) -> Vec<(&'static str, Vec<LintId>, bool)> {
+    pub fn get_lint_groups<'t>(
+        &'t self,
+    ) -> impl Iterator<Item = (&'static str, Vec<LintId>, bool)> + 't {
+        // This function is not used in a way which observes the order of lints.
+        #[cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
         self.lint_groups
             .iter()
             .filter(|(_, LintGroup { depr, .. })| {
@@ -154,7 +158,6 @@ impl LintStore {
             .map(|(k, LintGroup { lint_ids, from_plugin, .. })| {
                 (*k, lint_ids.clone(), *from_plugin)
             })
-            .collect()
     }
 
     pub fn register_early_pass(

compiler/rustc_lint/src/internal.rs

@@ -5,10 +5,7 @@ use crate::{EarlyContext, EarlyLintPass, LateContext, LateLintPass, LintContext}
 use rustc_ast as ast;
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
-use rustc_hir::{
-    GenericArg, HirId, Item, ItemKind, MutTy, Mutability, Node, Path, PathSegment, QPath, Ty,
-    TyKind,
-};
+use rustc_hir::*;
 use rustc_middle::ty;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::hygiene::{ExpnKind, MacroKind};
@@ -51,6 +48,60 @@ impl LateLintPass<'_> for DefaultHashTypes {
     }
 }
 
+declare_tool_lint! {
+    pub rustc::POTENTIAL_QUERY_INSTABILITY,
+    Allow,
+    "require explicit opt-in when using potentially unstable methods or functions",
+    report_in_external_macro: true
+}
+
+declare_lint_pass!(QueryStability => [POTENTIAL_QUERY_INSTABILITY]);
+
+impl LateLintPass<'_> for QueryStability {
+    fn check_expr(&mut self, cx: &LateContext<'_>, expr: &Expr<'_>) {
+        // FIXME(rustdoc): This lint uses typecheck results, causing rustdoc to
+        // error if there are resolution failures.
+        //
+        // As internal lints are currently always run if there are `unstable_options`,
+        // they are added to the lint store of rustdoc. Internal lints are also
+        // not used via the `lint_mod` query. Crate lints run outside of a query
+        // so rustdoc currently doesn't disable them.
+        //
+        // Instead of relying on this, either change crate lints to a query disabled by
+        // rustdoc, only run internal lints if the user is explicitly opting in
+        // or figure out a different way to avoid running lints for rustdoc.
+        if cx.tcx.sess.opts.actually_rustdoc {
+            return;
+        }
+
+        let (def_id, span) = match expr.kind {
+            ExprKind::Path(ref path) if let Some(def_id) = cx.qpath_res(path, expr.hir_id).opt_def_id() => {
+                (def_id, expr.span)
+            }
+            ExprKind::MethodCall(_, span, _, _) if let Some(def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) => {
+                (def_id, span)
+            },
+            _ => return,
+        };
+
+        let substs = cx.typeck_results().node_substs(expr.hir_id);
+        if let Ok(Some(instance)) = ty::Instance::resolve(cx.tcx, cx.param_env, def_id, substs) {
+            let def_id = instance.def_id();
+            if cx.tcx.has_attr(def_id, sym::rustc_lint_query_instability) {
+                cx.struct_span_lint(POTENTIAL_QUERY_INSTABILITY, span, |lint| {
+                    let msg = format!(
+                        "using `{}` can result in unstable query results",
+                        cx.tcx.item_name(def_id)
+                    );
+                    lint.build(&msg)
+                        .note("if you believe this case to be fine, allow this lint and add a comment explaining your rationale")
+                        .emit();
+                })
+            }
+        }
+    }
+}
+
 declare_tool_lint! {
     pub rustc::USAGE_OF_TY_TYKIND,
     Allow,

compiler/rustc_lint/src/lib.rs

@@ -31,12 +31,14 @@
 #![feature(box_patterns)]
 #![feature(crate_visibility_modifier)]
 #![feature(format_args_capture)]
+#![feature(if_let_guard)]
 #![feature(iter_order_by)]
 #![feature(iter_zip)]
 #![feature(never_type)]
 #![feature(nll)]
 #![feature(control_flow_enum)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate rustc_middle;
@@ -484,6 +486,8 @@ fn register_internals(store: &mut LintStore) {
     store.register_early_pass(|| Box::new(LintPassImpl));
     store.register_lints(&DefaultHashTypes::get_lints());
     store.register_late_pass(|| Box::new(DefaultHashTypes));
+    store.register_lints(&QueryStability::get_lints());
+    store.register_late_pass(|| Box::new(QueryStability));
     store.register_lints(&ExistingDocKeyword::get_lints());
     store.register_late_pass(|| Box::new(ExistingDocKeyword));
     store.register_lints(&TyTyKind::get_lints());
@@ -494,6 +498,7 @@ fn register_internals(store: &mut LintStore) {
         None,
         vec![
             LintId::of(DEFAULT_HASH_TYPES),
+            LintId::of(POTENTIAL_QUERY_INSTABILITY),
             LintId::of(USAGE_OF_TY_TYKIND),
             LintId::of(LINT_PASS_IMPL_WITHOUT_MACRO),
             LintId::of(TY_PASS_BY_REFERENCE),

compiler/rustc_metadata/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(try_blocks)]
 #![feature(never_type)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 extern crate proc_macro;
 

compiler/rustc_middle/src/lib.rs

@@ -55,6 +55,7 @@
 #![feature(try_reserve_kind)]
 #![feature(nonzero_ops)]
 #![recursion_limit = "512"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate bitflags;

compiler/rustc_mir_build/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(once_cell)]
 #![feature(min_specialization)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate tracing;

compiler/rustc_mir_transform/src/lib.rs

@@ -12,6 +12,7 @@
 #![feature(trusted_step)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate tracing;

compiler/rustc_monomorphize/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(control_flow_enum)]
 #![feature(in_band_lifetimes)]
 #![recursion_limit = "256"]
+#![cfg_attr(not(bootstrap), allow(rustc::potential_query_instability))]
 
 #[macro_use]
 extern crate tracing;