Crash at runtime rather than panicking when if condition is erroneous

Closes #5318

crates/compiler/mono/src/ir.rs

@@ -6613,12 +6613,16 @@ pub fn from_can<'a>(
             branches,
             final_else,
         } => {
-            let ret_layout = layout_cache
+            let ret_layout = return_on_layout_error!(
-                .from_var(env.arena, branch_var, env.subs)
+                env,
-                .expect("invalid ret_layout");
+                layout_cache.from_var(env.arena, branch_var, env.subs),
-            let cond_layout = layout_cache
+                "invalid return type in if expression"
-                .from_var(env.arena, cond_var, env.subs)
+            );
-                .expect("invalid cond_layout");
+            let cond_layout = return_on_layout_error!(
+                env,
+                layout_cache.from_var(env.arena, cond_var, env.subs),
+                "invalid condition type in if expression"
+            );
 
             let mut stmt = from_can(env, branch_var, final_else.value, procs, layout_cache);
 

crates/compiler/test_mono/generated/error_on_erroneous_condition.txt

@@ -0,0 +1,3 @@
+procedure Test.0 ():
+    let Test.2 : Str = "Erroneous: invalid condition type in if expression";
+    Crash Test.2

crates/compiler/test_mono/src/tests.rs

@@ -76,7 +76,7 @@ fn promote_expr_to_module(src: &str) -> String {
     buffer
 }
 
-fn compiles_to_ir(test_name: &str, src: &str, mode: &str, no_check: bool) {
+fn compiles_to_ir(test_name: &str, src: &str, mode: &str, allow_type_errors: bool, no_check: bool) {
     use roc_packaging::cache::RocCacheDir;
     use std::path::PathBuf;
 
@@ -146,7 +146,7 @@ fn compiles_to_ir(test_name: &str, src: &str, mode: &str, no_check: bool) {
         println!("Ignoring {} canonicalization problems", can_problems.len());
     }
 
-    assert!(type_problems.is_empty());
+    assert!(allow_type_errors || type_problems.is_empty());
 
     let main_fn_symbol = exposed_to_host.top_level_values.keys().copied().next();
 
@@ -2888,3 +2888,14 @@ fn layout_cache_structure_with_multiple_recursive_structures() {
         "#
     )
 }
+
+#[mono_test(allow_type_errors = "true")]
+fn error_on_erroneous_condition() {
+    indoc!(
+        r#"
+        app "test" provides [main] to "./platform"
+
+        main = if True then 1 else 2
+        "#
+    )
+}

crates/compiler/test_mono_macros/src/lib.rs

@@ -7,6 +7,7 @@ use quote::quote;
 #[proc_macro_attribute]
 pub fn mono_test(args: TokenStream, item: TokenStream) -> TokenStream {
     let mut no_check = false;
+    let mut allow_type_errors = false;
     let mut mode = "exec".to_owned();
     for arg in syn::parse_macro_input!(args as syn::AttributeArgs) {
         use syn::{Lit, Meta, MetaNameValue, NestedMeta};
@@ -22,6 +23,9 @@ pub fn mono_test(args: TokenStream, item: TokenStream) -> TokenStream {
             if path.is_ident("no_check") {
                 no_check = true;
             }
+            if path.is_ident("allow_type_errors") {
+                allow_type_errors = true;
+            }
         }
     }
 
@@ -40,7 +44,7 @@ pub fn mono_test(args: TokenStream, item: TokenStream) -> TokenStream {
         #[test]
         #(#attributes)*
         #visibility fn #name(#args) {
-            compiles_to_ir(#name_str, #body, &#mode, #no_check);
+            compiles_to_ir(#name_str, #body, &#mode, #allow_type_errors, #no_check);
 
         }
     };