[Linter] Unnecessary while loop (#16876)

# Description
This linter encourages replacing `while(true)` loops with the more
idiomatic loop construct. Here's a breakdown of how it works:
It checks each expression in the AST.
If the expression is a While loop, it examines the condition.
If the condition is always true (using the `is_condition_always_true`
function), it reports a diagnostic suggesting to use loop instead.

The `is_condition_always_true` function checks if the condition is a
boolean literal with the value true.

## Test plan
Added more use case including false positive, false negative case

## Release notes

- [ ] Protocol: 
- [ ] Nodes (Validators and Full nodes): 
- [ ] Indexer: 
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [X] CLI: Move will now lint against `while (true)`, which should be
replaced by `loop`
- [ ] Rust SDK:

---------

Co-authored-by: jamedzung <[email protected]>
Co-authored-by: Todd Nowacki <[email protected]>

external-crates/move/crates/move-compiler/src/linters/mod.rs

@@ -8,6 +8,7 @@ use crate::{
     linters::constant_naming::ConstantNamingVisitor, typing::visitor::TypingVisitor,
 };
 pub mod constant_naming;
+mod unnecessary_while_loop;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum LintLevel {
@@ -34,26 +35,39 @@ pub const ALLOW_ATTR_CATEGORY: &str = "lint";
 pub const LINT_WARNING_PREFIX: &str = "Lint ";
 pub const CONSTANT_NAMING_FILTER_NAME: &str = "constant_naming";
 pub const CONSTANT_NAMING_DIAG_CODE: u8 = 1;
+pub const WHILE_TRUE_TO_LOOP_FILTER_NAME: &str = "while_true";
+pub const WHILE_TRUE_TO_LOOP_DIAG_CODE: u8 = 4;
 
 pub fn known_filters() -> (Option<Symbol>, Vec<WarningFilter>) {
     (
         Some(ALLOW_ATTR_CATEGORY.into()),
-        vec![WarningFilter::code(
-            Some(LINT_WARNING_PREFIX),
-            LinterDiagnosticCategory::Style as u8,
-            CONSTANT_NAMING_DIAG_CODE,
-            Some(CONSTANT_NAMING_FILTER_NAME),
-        )],
+        vec![
+            WarningFilter::code(
+                Some(LINT_WARNING_PREFIX),
+                LinterDiagnosticCategory::Style as u8,
+                CONSTANT_NAMING_DIAG_CODE,
+                Some(CONSTANT_NAMING_FILTER_NAME),
+            ),
+            WarningFilter::code(
+                Some(LINT_WARNING_PREFIX),
+                LinterDiagnosticCategory::Complexity as u8,
+                WHILE_TRUE_TO_LOOP_DIAG_CODE,
+                Some(WHILE_TRUE_TO_LOOP_FILTER_NAME),
+            ),
+        ],
     )
 }
 
 pub fn linter_visitors(level: LintLevel) -> Vec<Visitor> {
     match level {
         LintLevel::None | LintLevel::Default => vec![],
         LintLevel::All => {
-            vec![constant_naming::ConstantNamingVisitor::visitor(
-                ConstantNamingVisitor,
-            )]
+            vec![
+                constant_naming::ConstantNamingVisitor::visitor(ConstantNamingVisitor),
+                unnecessary_while_loop::WhileTrueToLoop::visitor(
+                    unnecessary_while_loop::WhileTrueToLoop,
+                ),
+            ]
         }
     }
 }

external-crates/move/crates/move-compiler/src/linters/unnecessary_while_loop.rs

@@ -0,0 +1,68 @@
+//! Encourages replacing `while(true)` with `loop` for infinite loops in Move for clarity and conciseness.
+//! Identifies `while(true)` patterns, suggesting a more idiomatic approach using `loop`.
+//! Aims to enhance code readability and adherence to Rust idioms.
+use crate::{
+    diag,
+    diagnostics::{
+        codes::{custom, DiagnosticInfo, Severity},
+        WarningFilters,
+    },
+    expansion::ast::Value_,
+    shared::CompilationEnv,
+    typing::{
+        ast::{self as T, UnannotatedExp_},
+        visitor::{TypingVisitorConstructor, TypingVisitorContext},
+    },
+};
+
+use super::{LinterDiagnosticCategory, LINT_WARNING_PREFIX, WHILE_TRUE_TO_LOOP_DIAG_CODE};
+
+const WHILE_TRUE_TO_LOOP_DIAG: DiagnosticInfo = custom(
+    LINT_WARNING_PREFIX,
+    Severity::Warning,
+    LinterDiagnosticCategory::Complexity as u8,
+    WHILE_TRUE_TO_LOOP_DIAG_CODE,
+    "unnecessary 'while (true)', replace with 'loop'",
+);
+
+pub struct WhileTrueToLoop;
+
+pub struct Context<'a> {
+    env: &'a mut CompilationEnv,
+}
+
+impl TypingVisitorConstructor for WhileTrueToLoop {
+    type Context<'a> = Context<'a>;
+
+    fn context<'a>(env: &'a mut CompilationEnv, _program: &T::Program) -> Self::Context<'a> {
+        Context { env }
+    }
+}
+
+impl TypingVisitorContext for Context<'_> {
+    fn add_warning_filter_scope(&mut self, filter: WarningFilters) {
+        self.env.add_warning_filter_scope(filter)
+    }
+    fn pop_warning_filter_scope(&mut self) {
+        self.env.pop_warning_filter_scope()
+    }
+
+    fn visit_exp_custom(&mut self, exp: &mut T::Exp) -> bool {
+        let UnannotatedExp_::While(_, cond, _) = &exp.exp.value else {
+            return false;
+        };
+        let UnannotatedExp_::Value(sp!(_, Value_::Bool(true))) = &cond.exp.value else {
+            return false;
+        };
+
+        let msg = "'while (true)' can be always replaced with 'loop'";
+        let mut diag = diag!(WHILE_TRUE_TO_LOOP_DIAG, (exp.exp.loc, msg));
+        diag.add_note(
+            "A 'loop' is more useful in these cases. Unlike 'while', 'loop' can have a \
+            'break' with a value, e.g. 'let x = loop { break 42 };'",
+        );
+        self.env.add_diag(diag);
+
+        false
+    }
+}

external-crates/move/crates/move-compiler/tests/linter/false_negative_unnecessary_while_loop.move

@@ -0,0 +1,11 @@
+module 0x42::loop_test {
+
+    // These should trigger but currently dont
+    public fun false_negative_obfuscated_true() {
+        let always_true = true;
+        while (always_true) {};
+        while (true && true) {};
+        while (true || false) {};
+        while (1 > 0) {};
+    }
+}

external-crates/move/crates/move-compiler/tests/linter/suppress_unnecessary_while_loop.move

@@ -0,0 +1,7 @@
+module 0x42::loop_test {
+
+    #[allow(lint(while_true))]
+    public fun suppressed_while_true() {
+        while (true) {};
+    }
+}

external-crates/move/crates/move-compiler/tests/linter/true_negative_unnecessary_while_loop.move

@@ -0,0 +1,11 @@
+module 0x42::loop_test {
+
+    public fun true_negative_while_with_condition() {
+        let b = false;
+        while (false) {};
+        while (b) {};
+        while (false && true) {};
+        while (false || false) {};
+        while (0 > 1) {};
+    }
+}

external-crates/move/crates/move-compiler/tests/linter/true_positive_unnecessary_while_loop.exp

@@ -0,0 +1,18 @@
+warning[Lint W01004]: unnecessary 'while (true)', replace with 'loop'
+  ┌─ tests/linter/true_positive_unnecessary_while_loop.move:3:9
+  │
+3 │         while (true) {};
+  │         ^^^^^^^^^^^^^^^ 'while (true)' can be always replaced with 'loop'
+  │
+  = A 'loop' is more useful in these cases. Unlike 'while', 'loop' can have a 'break' with a value, e.g. 'let x = loop { break 42 };'
+  = This warning can be suppressed with '#[allow(lint(while_true))]' applied to the 'module' or module member ('const', 'fun', or 'struct')
+
+warning[Lint W01004]: unnecessary 'while (true)', replace with 'loop'
+  ┌─ tests/linter/true_positive_unnecessary_while_loop.move:4:9
+  │
+4 │         while (true) { break }
+  │         ^^^^^^^^^^^^^^^^^^^^^^ 'while (true)' can be always replaced with 'loop'
+  │
+  = A 'loop' is more useful in these cases. Unlike 'while', 'loop' can have a 'break' with a value, e.g. 'let x = loop { break 42 };'
+  = This warning can be suppressed with '#[allow(lint(while_true))]' applied to the 'module' or module member ('const', 'fun', or 'struct')
+

external-crates/move/crates/move-compiler/tests/linter/true_positive_unnecessary_while_loop.move

@@ -0,0 +1,6 @@
+module 0x42::loop_test {
+    public fun true_positive_infinite_loop() {
+        while (true) {};
+        while (true) { break }
+    }
+}