fix: type inference for user-defined module function return types (#811)

The inferModuleCallType() function only handled stdlib modules and
returned empty types for user-defined modules. This caused type
mismatch errors when variables were assigned from user module
function calls without explicit type annotations.

Now uses GetModuleFunction() to look up user-defined module function
signatures and properly infer return types.

Fixes #807

Author: SchoolyB

integration-tests/pass/multi-file/user-module-type-inference/main.ez

@@ -0,0 +1,48 @@
+/*
+ * main.ez - Test type inference for user-defined module function return types
+ *
+ * Tests issue #807: Type inference fails for user-defined module function return types
+ */
+module main
+
+import & use @std
+import & use lib"./mylib"
+
+do needs_u64(v u64) {
+    println("Got u64: ${v}")
+}
+
+do needs_string(s string) {
+    println("Got string: ${s}")
+}
+
+do needs_float(f float) {
+    println("Got float: ${f}")
+}
+
+do main() {
+    println("========================================")
+    println("  User Module Type Inference Test")
+    println("========================================")
+    println("")
+
+    // Test 1: Type inference from user module function returning u64
+    temp val = lib.get_value()  // Type should be inferred as u64
+    needs_u64(val)              // Should work without explicit type
+    println("Test 1 PASSED: u64 type inference")
+
+    // Test 2: Type inference from user module function returning string
+    temp str = lib.get_string()  // Type should be inferred as string
+    needs_string(str)
+    println("Test 2 PASSED: string type inference")
+
+    // Test 3: Type inference from user module function returning float
+    temp flt = lib.get_float()  // Type should be inferred as float
+    needs_float(flt)
+    println("Test 3 PASSED: float type inference")
+
+    println("")
+    println("========================================")
+    println("  All Tests PASSED!")
+    println("========================================")
+}

integration-tests/pass/multi-file/user-module-type-inference/mylib.ez

@@ -0,0 +1,16 @@
+/*
+ * mylib.ez - Test module for type inference from user-defined modules
+ */
+module mylib
+
+do get_value() -> u64 {
+    return 42
+}
+
+do get_string() -> string {
+    return "hello"
+}
+
+do get_float() -> float {
+    return 3.14
+}

pkg/typechecker/typechecker.go

@@ -4725,6 +4725,13 @@ func (tc *TypeChecker) inferModuleCallType(member *ast.MemberExpression, args []
 	case "time":
 		return tc.inferTimeCallType(funcName, args)
 	default:
+		// Check user-defined modules
+		if sig, ok := tc.GetModuleFunction(moduleName, funcName); ok {
+			if len(sig.ReturnTypes) >= 1 {
+				return sig.ReturnTypes[0], true
+			}
+			return "void", true
+		}
 		return "", false
 	}
 }