Merge pull request #385 from ribru17/unnecessary_if

feat: diagnostics for unnecessary "if" conditions

Author: CppCXY

crates/emmylua_code_analysis/locales/lint.yml

@@ -213,6 +213,14 @@ Cannot use `...` outside a vararg function.:
   en: 'Impossible assert: this expression is always falsy; prefer `error()`'
   zh_CN: '不可能的断言: 该表达式始终为假；建议使用 `error()`'
   zh_HK: '不可能的斷言: 該表達式始終為假；建議使用 `error()`'
+'Unnecessary `if` statement: this condition is always truthy':
+  en: 'Unnecessary `if` statement: this condition is always truthy'
+  zh_CN: '不必要的 `if` 语句：此条件始终为真'
+  zh_HK: '不必要的 `if` 陳述式：此條件始終為真'
+'Impossible `if` statement: this condition is always falsy':
+  en: 'Impossible `if` statement: this condition is always falsy'
+  zh_CN: '不可能的 `if` 语句：此条件始终为假'
+  zh_HK: '不可能的 `if` 陳述式：此條件始終為假'
 "`...` should be the last arg.":
   en: "`...` should be the last arg."
   zh_CN: "`...`必须是最后一个参数。"

crates/emmylua_code_analysis/resources/schema.json

@@ -466,6 +466,13 @@
           "enum": [
             "unnecessary-assert"
           ]
+        },
+        {
+          "description": "unnecessary-if",
+          "type": "string",
+          "enum": [
+            "unnecessary-if"
+          ]
         }
       ]
     },

crates/emmylua_code_analysis/src/diagnostic/checker/mod.rs

@@ -24,6 +24,7 @@ mod unbalanced_assignments;
 mod undefined_doc_param;
 mod undefined_global;
 mod unnecessary_assert;
+mod unnecessary_if;
 mod unused;
 
 use emmylua_parser::{
@@ -65,6 +66,7 @@ pub fn check_file(context: &mut DiagnosticContext, semantic_model: &SemanticMode
     run_check::<deprecated::DeprecatedChecker>(context, semantic_model);
     run_check::<undefined_global::UndefinedGlobalChecker>(context, semantic_model);
     run_check::<unnecessary_assert::UnnecessaryAssertChecker>(context, semantic_model);
+    run_check::<unnecessary_if::UnnecessaryIfChecker>(context, semantic_model);
     run_check::<access_invisible::AccessInvisibleChecker>(context, semantic_model);
     run_check::<local_const_reassign::LocalConstReassignChecker>(context, semantic_model);
     run_check::<discard_returns::DiscardReturnsChecker>(context, semantic_model);

crates/emmylua_code_analysis/src/diagnostic/checker/unnecessary_if.rs

@@ -0,0 +1,50 @@
+use emmylua_parser::{LuaAstNode, LuaExpr, LuaIfStat};
+
+use crate::{DiagnosticCode, LuaType, SemanticModel};
+
+use super::{Checker, DiagnosticContext};
+
+pub struct UnnecessaryIfChecker;
+
+impl Checker for UnnecessaryIfChecker {
+    const CODES: &[DiagnosticCode] = &[DiagnosticCode::UnnecessaryIf];
+
+    fn check(context: &mut DiagnosticContext, semantic_model: &SemanticModel) {
+        let root = semantic_model.get_root().clone();
+        for if_statement in root.descendants::<LuaIfStat>() {
+            if let Some(condition) = if_statement.get_condition_expr() {
+                check_condition(context, semantic_model, condition);
+            }
+            for clause in if_statement.get_else_if_clause_list() {
+                if let Some(condition) = clause.get_condition_expr() {
+                    check_condition(context, semantic_model, condition);
+                }
+            }
+        }
+    }
+}
+
+fn check_condition(
+    context: &mut DiagnosticContext,
+    semantic_model: &SemanticModel,
+    condition: LuaExpr,
+) -> Option<()> {
+    let expr_type = semantic_model.infer_expr(condition.clone()).ok()?;
+
+    if expr_type.is_always_truthy() {
+        context.add_diagnostic(
+            DiagnosticCode::UnnecessaryIf,
+            condition.get_range(),
+            t!("Unnecessary `if` statement: this condition is always truthy").to_string(),
+            None,
+        );
+    } else if expr_type.is_always_falsy() {
+        context.add_diagnostic(
+            DiagnosticCode::UnnecessaryIf,
+            condition.get_range(),
+            t!("Impossible `if` statement: this condition is always falsy").to_string(),
+            None,
+        );
+    }
+    Some(())
+}

crates/emmylua_code_analysis/src/diagnostic/lua_diagnostic_code.rs

@@ -90,6 +90,8 @@ pub enum DiagnosticCode {
     UnbalancedAssignments,
     /// unnecessary-assert
     UnnecessaryAssert,
+    /// unnecessary-if
+    UnnecessaryIf,
 
     #[serde(other)]
     None,