ffix(lint/noInferrableTypes): assume TypeScript unsafe null mode (#729)

biomejs · Nov 14, 2023 · 80a7987 · 80a7987
1 parent fc877aa
commit 80a7987
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -52,6 +52,8 @@ Read our [guidelines for writing a good changelog entry](https://github.com/biom
 
 - Fix [#455](https://github.com/biomejs/biome/issues/455). The CLI can now print complex emojis to the console correctly.
 
+- Fix [#727](https://github.com/biomejs/biome/issues/727). [noInferrableTypes](https://biomejs.dev/linter/rules/no-inferrable-types) now correctly keeps type annotations when the initialization expression is `null`. Contributed by @Conaclos
+
 ### Parser
 
 ### VSCode

diff --git a/crates/biome_js_analyze/src/analyzers/style/no_inferrable_types.rs b/crates/biome_js_analyze/src/analyzers/style/no_inferrable_types.rs
@@ -10,6 +10,7 @@ use biome_js_syntax::{
     JsVariableDeclarator, JsVariableDeclaratorList, TsPropertyParameter, TsReadonlyModifier,
     TsTypeAnnotation,
 };
+use biome_js_syntax::{AnyJsLiteralExpression, AnyTsType};
 use biome_rowan::AstNode;
 use biome_rowan::BatchMutationExt;
 
@@ -149,9 +150,24 @@ impl Rule for NoInferrableTypes {
                 // In const contexts, literal type annotations are rejected.
                 // e.g. `const x: 1 = <literal>`
                 //
+                // However, we ignore `null` and `undefined` literal types,
+                // because in unsafe null mode, TypeScript widen an unannotated variable to `any`.
+                //
                 // In non-const contexts, wide type annotation are rejected.
                 // e.g. `let x: number = <literal>`
-                if (is_const && ty.is_literal_type()) || (!is_const && ty.is_primitive_type()) {
+                //
+                // However, we ignore the case where <literal> is `null`,
+                // because in unsafe null mode, it is possible to assign `null` and `undefined` to any type.
+                if (is_const && is_non_null_literal_type(&ty))
+                    || (!is_const
+                        && ty.is_primitive_type()
+                        && !matches!(
+                            init_expr,
+                            AnyJsExpression::AnyJsLiteralExpression(
+                                AnyJsLiteralExpression::JsNullLiteralExpression(_)
+                            )
+                        ))
+                {
                     return Some(type_annotation);
                 }
             }
@@ -206,3 +222,13 @@ fn has_trivially_inferrable_type(expr: &AnyJsExpression) -> Option<()> {
         _ => None,
     }
 }
+
+fn is_non_null_literal_type(ty: &AnyTsType) -> bool {
+    matches!(
+        ty,
+        AnyTsType::TsBooleanLiteralType(_)
+            | AnyTsType::TsBigintLiteralType(_)
+            | AnyTsType::TsNumberLiteralType(_)
+            | AnyTsType::TsStringLiteralType(_)
+    )
+}
diff --git a/crates/biome_js_analyze/tests/specs/style/noInferrableTypes/invalid.ts b/crates/biome_js_analyze/tests/specs/style/noInferrableTypes/invalid.ts
@@ -9,15 +9,13 @@ const x: false = !1;
 const x: true = true;
 const x: true = !false;
 const x: true = !0;
-const x: null = null;
 const x: 1 = +1;
 const x: -1 = -1;
 const x: 1e-5 = 1e-5;
 const x: RegExp = /a/;
 const x: "str" = "str";
 const x: "str" = `str`; // constant template string
 const x: "str2" = `str${f()}`;
-const x: undefined = void f();
 
 class X {
 	readonly x: 1 = 1;