Linter: Warn about strict balance equality (#1914)

* feat(linter): strict balance equality lint

The current implementation works only with intraprocedural MIR and does
not support taint propagation across function calls.

Closes #1811

* feat(lint): Handle temporary values resulted after Rvalue::Use

* fix(lint): spans to emit diagnostics

Previously, diagnostics did not work, since `terminator.span` is
resulted after macro expansion

* feat(tests): more tests

* feat(lint): Manually traverse functions in user-defined code

This is required to implement interprocedural analysis

* feat(lint): interprocedural analysis that finds tainted returns

* fix(lint): recursive calls in interprocedural analysis

* fix(lint): false negative on `CheckedBinaryOp`

* feat(lint): propagation through references

* feat(lint): Propagate tainted values through `&mut` arguments

* chore(lint): docstring, comments

* feat(lint): handle comparison of references in functions

* chore(tests): comments

* feat(lint+tests): updated `pass` test, fixed binop conditions

* feat(tests): test for lint suppressions

* chore(tests): fmt

* chore(tests): fmt

* chore: Add changelog entry

* chore(lint): Reuse utility functions introduced in #1932

* chore: Fix changelog

* chore: Fix comments

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 - Linter: `storage_never_freed` lint - [#1932](https://github.com/paritytech/ink/pull/1932)
+- Linter: `strict_balance_equality` lint - [#1914](https://github.com/paritytech/ink/pull/1914)
 
 ## Version 5.0.0-alpha
 

linting/Cargo.toml

@@ -57,6 +57,12 @@ path = "ui/pass/storage_never_freed.rs"
 [[example]]
 name = "storage_never_freed_fail"
 path = "ui/fail/storage_never_freed.rs"
+[[example]]
+name = "strict_balance_equality_pass"
+path = "ui/pass/strict_balance_equality.rs"
+[[example]]
+name = "strict_balance_equality_fail"
+path = "ui/fail/strict_balance_equality.rs"
 
 [package.metadata.rust-analyzer]
 rustc_private = true

linting/src/ink_utils.rs

@@ -11,6 +11,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
 use clippy_utils::match_def_path;
 use if_chain::if_chain;
 use rustc_hir::{
@@ -51,7 +52,6 @@ pub(crate) fn find_storage_struct(
         .copied()
 }
 
-// TODO: Extracted from #1914; reuse this in #1914 when it is merged
 /// Returns `ItemId`s defined inside the code block of `const _: () = {}`.
 ///
 /// The Rust code expanded after ink! code generation used these to define different
@@ -77,7 +77,6 @@ fn items_in_unnamed_const(cx: &LateContext<'_>, id: &ItemId) -> Vec<ItemId> {
     }
 }
 
-// TODO: Extracted from #1914; reuse this in #1914 when it is merged
 /// Collect all the `ItemId`s in nested `const _: () = {}`
 pub(crate) fn expand_unnamed_consts(
     cx: &LateContext<'_>,
@@ -90,7 +89,6 @@ pub(crate) fn expand_unnamed_consts(
     })
 }
 
-// TODO: Extracted from #1914; reuse this in #1914 when it is merged
 /// Finds type of the struct that implements a contract with user-defined code
 fn find_contract_ty_hir<'tcx>(
     cx: &LateContext<'tcx>,
@@ -114,7 +112,6 @@ fn find_contract_ty_hir<'tcx>(
         .copied()
 }
 
-// TODO: Extracted from #1914; reuse this in #1914 when it is merged
 /// Compares types of two user-defined structs
 fn eq_hir_struct_tys(lhs: &Ty<'_>, rhs: &Ty<'_>) -> bool {
     match (lhs.kind, rhs.kind) {
@@ -126,7 +123,6 @@ fn eq_hir_struct_tys(lhs: &Ty<'_>, rhs: &Ty<'_>) -> bool {
     }
 }
 
-// TODO: Extracted from #1914; reuse this in #1914 when it is merged
 /// Finds an ID of the implementation of the contract struct containing user-defined code
 pub(crate) fn find_contract_impl_id(
     cx: &LateContext<'_>,

linting/src/lib.rs

@@ -17,20 +17,24 @@
     html_favicon_url = "https://use.ink/crate-docs/favicon.png"
 )]
 #![feature(rustc_private)]
+#![feature(box_patterns)]
 
 dylint_linting::dylint_library!();
 
 extern crate rustc_ast;
 extern crate rustc_errors;
 extern crate rustc_hir;
+extern crate rustc_index;
 extern crate rustc_lint;
 extern crate rustc_middle;
+extern crate rustc_mir_dataflow;
 extern crate rustc_session;
 extern crate rustc_span;
 
 mod ink_utils;
 mod primitive_topic;
 mod storage_never_freed;
+mod strict_balance_equality;
 
 #[doc(hidden)]
 #[no_mangle]
@@ -41,9 +45,12 @@ pub fn register_lints(
     lint_store.register_lints(&[
         primitive_topic::PRIMITIVE_TOPIC,
         storage_never_freed::STORAGE_NEVER_FREED,
+        strict_balance_equality::STRICT_BALANCE_EQUALITY,
     ]);
     lint_store.register_late_pass(|_| Box::new(primitive_topic::PrimitiveTopic));
     lint_store.register_late_pass(|_| Box::new(storage_never_freed::StorageNeverFreed));
+    lint_store
+        .register_late_pass(|_| Box::new(strict_balance_equality::StrictBalanceEquality));
 }
 
 #[test]

linting/src/primitive_topic.rs

@@ -11,6 +11,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
 use clippy_utils::{
     diagnostics::span_lint_and_then,
     is_lint_allowed,

linting/src/storage_never_freed.rs

@@ -11,6 +11,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
 use crate::ink_utils::{
     expand_unnamed_consts,
     find_contract_impl_id,