feat(selfhost-sema): check annotation vs initializer type in let/var

_test_error_recovery/src/Main.bux

@@ -1,5 +1,6 @@
 func Main() -> int {
-    let bad: int = "a" + 1;
+    let x: int = "hello";
+    let y: bool = 42;
     let z: int = undefined_variable;
     return 0;
 }

src/sema.bux

@@ -198,6 +198,33 @@ module Sema {
         return kind == tyBool || kind == tyBool8 || kind == tyBool16 || kind == tyBool32;
     }
 
+    // Strict numeric predicate for assignment checking: unlike Sema_IsNumeric,
+    // this does NOT treat tyNamed/tyTypeParam as numeric.
+    func Sema_IsStrictNumeric(kind: int) -> bool {
+        if kind == tyInt8 || kind == tyInt16 || kind == tyInt32 || kind == tyInt64 || kind == tyInt { return true; }
+        if kind == tyUInt8 || kind == tyUInt16 || kind == tyUInt32 || kind == tyUInt64 || kind == tyUInt { return true; }
+        if kind == tyFloat32 || kind == tyFloat64 { return true; }
+        return false;
+    }
+
+    // Display-name helper for assignment diagnostics.
+    func Sema_TypeNameForDiag(te: *TypeExpr, kind: int) -> String {
+        if te != null as *TypeExpr {
+            if te.kind == tekPointer && te.pointerPointee != null as *TypeExpr {
+                return String_Concat(te.pointerPointee.typeName, "*");
+            }
+            if !String_Eq(te.typeName, "") { return te.typeName; }
+        }
+        if kind == tyBool { return "bool"; }
+        if kind == tyStr { return "String"; }
+        if kind == tyInt { return "int"; }
+        if kind == tyInt64 { return "int64"; }
+        if kind == tyUInt { return "uint"; }
+        if kind == tyFloat64 { return "float64"; }
+        if kind == tyPointer { return "*void"; }
+        return "?";
+    }
+
     // ---------------------------------------------------------------------------
     // Block checking helper
     // ---------------------------------------------------------------------------
@@ -1466,6 +1493,37 @@ module Sema {
                     sym.typeName = stmt.child1.refType.typeName;
                 }
             }
+            // Assignment check: annotation vs initializer (skip when either side is unknown)
+            if stmt.refStmtType != null as *TypeExpr && initType != tyUnknown {
+                let annotKind: int = Sema_ResolveType(sema, stmt.refStmtType);
+                if annotKind != tyUnknown {
+                    var mismatch: bool = false;
+                    if initType == tyNamed && annotKind == tyNamed {
+                        // Both named: kinds are equal, compare type names (when available).
+                        if stmt.child1 != null as *Expr && stmt.child1.refType != null as *TypeExpr {
+                            if !String_Eq(stmt.child1.refType.typeName, "") &&
+                            !String_Eq(stmt.child1.refType.typeName, stmt.refStmtType.typeName) {
+                                mismatch = true;
+                            }
+                        }
+                    } else if initType != annotKind {
+                        let numericOk: bool = Sema_IsStrictNumeric(initType) && Sema_IsStrictNumeric(annotKind);
+                        let initIsPtr: bool = initType == tyPointer || initType == tyStr;
+                        let annotIsPtr: bool = annotKind == tyPointer || annotKind == tyStr;
+                        let ptrOk: bool = initIsPtr && annotIsPtr;
+                        if !numericOk && !ptrOk {
+                            mismatch = true;
+                        }
+                    }
+                    if mismatch {
+                        let gotName: String = Sema_TypeNameForDiag(stmt.child1.refType, initType);
+                        let wantName: String = Sema_TypeNameForDiag(stmt.refStmtType, annotKind);
+                        let msg: String = String_Concat("cannot assign ",
+                            String_Concat(gotName, String_Concat(" to ", wantName)));
+                        Sema_EmitError(sema, stmt.line, stmt.column, msg);
+                    }
+                }
+            }
             sym.isMutable = stmt.boolValue;
             sym.isPublic = false;
             sym.decl = null as *Decl;