fix(designer): specify temporary variable types to prevent type deduction failures

Addresses type errors in generated code that occurred in certain use
cases.

Author: yvt

tcw3/designer/src/codegen/implgen/initgen.rs

@@ -5,6 +5,7 @@ use pathfinding::directed::{
     strongly_connected_components::strongly_connected_components,
     topological_sort::topological_sort,
 };
+use quote::ToTokens;
 use std::{cell::Cell, collections::HashMap, fmt::Write, ops::Range};
 use try_match::try_match;
 
@@ -1044,7 +1045,7 @@ pub fn gen_construct(
 
             DepNode::Field { item_i } => {
                 let field = comp.items[*item_i].field().unwrap();
-                write!(out, "let {} = ", var).unwrap();
+                write!(out, "let {}: {} = ", var, field.ty.to_token_stream()).unwrap();
 
                 if field.value.is_none() {
                     // Mandatory field - the value is always available

tcw3/designer/tests_impl/field/bug_type_deduction.rs

@@ -0,0 +1 @@
+designer_impl! { crate::field::bug_type_deduction::Comp }

tcw3/designer/tests_impl/field/bug_type_deduction.tcwdl

@@ -0,0 +1,17 @@
+use tcw3::pal;
+comp crate::field::bug_type_deduction::Comp {
+    const wm: pal::Wm { set; }
+
+    // An old implementation of Designer produced implementation code
+    // that didn't type-check for these fields:
+    //
+    //  error[E0282]: type annotations needed
+    //      |
+    //  695 | let __tmp_1 = match () { () => { "a" . into ( ) } };
+    //      |     ------- consider giving `__tmp_1` a type
+    //  696 | let __tmp_2 = match ((&__tmp_1), ) { (_input_0, ) => { _input_0 . len ( ) } };
+    //      |                                                                   ^^^ cannot infer type
+    //
+    const const1: String = "a".into();
+    const const2: usize = get!(&const1).len();
+}

tcw3/designer/tests_impl/lib.rs

@@ -10,6 +10,7 @@ mod commit {
 
 mod field {
     mod accessors;
+    mod bug_type_deduction;
     mod lifetime_elision;
     mod prop;
 }

tcw3/designer/tests_impl/lib.tcwdl

@@ -1,5 +1,6 @@
 import!("commit/remotetrigger.tcwdl");
 import!("field/accessors.tcwdl");
+import!("field/bug_type_deduction.tcwdl");
 import!("field/lifetime_elision.tcwdl");
 import!("field/prop.tcwdl");
 import!("func/inline.tcwdl");