Improves DCA warnings after divergent expressions.

sway-core/src/control_flow_analysis/dead_code_analysis.rs

@@ -1331,6 +1331,7 @@ fn connect_expression<'eng: 'cfg, 'cfg>(
                 )?;
             }
 
+            let mut args_diverge = false;
             // we evaluate every one of the function arguments
             for (_name, arg) in arguments {
                 let span = arg.span.clone();
@@ -1345,6 +1346,10 @@ fn connect_expression<'eng: 'cfg, 'cfg>(
                     span,
                     options,
                 )?;
+
+                if type_engine.get(arg.return_type).contains_never(engines) {
+                    args_diverge = true;
+                }
             }
             options.force_struct_fields_connection = force_struct_fields_connection;
 
@@ -1363,16 +1368,20 @@ fn connect_expression<'eng: 'cfg, 'cfg>(
                     }
                 }
             }
-            // the exit points get connected to an exit node for the application
-            if !is_external {
-                if let Some(exit_node) = exit_node {
-                    graph.add_edge(fn_exit_point, exit_node, "".into());
-                    Ok(vec![exit_node])
+            if args_diverge {
+                Ok(vec![])
+            } else {
+                // the exit points get connected to an exit node for the application
+                if !is_external {
+                    if let Some(exit_node) = exit_node {
+                        graph.add_edge(fn_exit_point, exit_node, "".into());
+                        Ok(vec![exit_node])
+                    } else {
+                        Ok(vec![fn_exit_point])
+                    }
                 } else {
-                    Ok(vec![fn_exit_point])
+                    Ok(vec![fn_entrypoint])
                 }
-            } else {
-                Ok(vec![fn_entrypoint])
             }
         }
         LazyOperator { lhs, rhs, .. } => {
@@ -1711,9 +1720,14 @@ fn connect_expression<'eng: 'cfg, 'cfg>(
             elem_type: _,
             contents,
         } => {
+            let mut element_diverge = false;
             let nodes = contents
                 .iter()
                 .map(|elem| {
+                    if !element_diverge && type_engine.get(elem.return_type).contains_never(engines)
+                    {
+                        element_diverge = true
+                    }
                     connect_expression(
                         engines,
                         &elem.expression,
@@ -1727,7 +1741,11 @@ fn connect_expression<'eng: 'cfg, 'cfg>(
                     )
                 })
                 .collect::<Result<Vec<_>, _>>()?;
-            Ok(nodes.concat())
+            if element_diverge {
+                Ok(vec![])
+            } else {
+                Ok(nodes.concat())
+            }
         }
         ArrayIndex { prefix, index } => {
             let prefix_idx = connect_expression(
@@ -1843,13 +1861,15 @@ fn connect_expression<'eng: 'cfg, 'cfg>(
 
             let while_loop_exit = graph.add_node("while loop exit".to_string().into());
 
-            // it is possible for a whole while loop to be skipped so add edge from
-            // beginning of while loop straight to exit
-            graph.add_edge(
-                entry,
-                while_loop_exit,
-                "condition is initially false".into(),
-            );
+            if !matches!(*type_engine.get(condition.return_type), TypeInfo::Never) {
+                // it is possible for a whole while loop to be skipped so add edge from
+                // beginning of while loop straight to exit
+                graph.add_edge(
+                    entry,
+                    while_loop_exit,
+                    "condition is initially false".into(),
+                );
+            }
             let mut leaves = vec![entry];
 
             // handle the condition of the loop
@@ -2087,6 +2107,7 @@ fn connect_enum_instantiation<'eng: 'cfg, 'cfg>(
         graph.add_edge(*leaf, enum_instantiation_entry_idx, "".into());
     }
 
+    let mut is_variant_unreachable = false;
     // add edge from the entry of the enum instantiation to the body of the instantiation
     if let Some(instantiator) = contents {
         let instantiator_contents = connect_expression(
@@ -2100,13 +2121,23 @@ fn connect_enum_instantiation<'eng: 'cfg, 'cfg>(
             enum_decl.span.clone(),
             options,
         )?;
+        if engines
+            .te()
+            .get(instantiator.return_type)
+            .contains_never(engines)
+        {
+            is_variant_unreachable = true;
+        }
+
         for leaf in instantiator_contents {
             graph.add_edge(leaf, enum_instantiation_exit_idx, "".into());
         }
     }
 
     graph.add_edge(decl_ix, variant_index, "".into());
-    graph.add_edge(variant_index, enum_instantiation_exit_idx, "".into());
+    if !is_variant_unreachable {
+        graph.add_edge(variant_index, enum_instantiation_exit_idx, "".into());
+    }
 
     Ok(vec![enum_instantiation_exit_idx])
 }

sway-core/src/type_system/info.rs

@@ -1156,6 +1156,43 @@ impl TypeInfo {
         matches!(self, TypeInfo::Tuple(_))
     }
 
+    pub fn contains_never(&self, engines: &Engines) -> bool {
+        match self {
+            TypeInfo::Never => true,
+            TypeInfo::Tuple(type_arguments) => type_arguments
+                .iter()
+                .any(|t| engines.te().get(t.type_id).contains_never(engines)),
+            TypeInfo::Array(type_argument, _) => engines
+                .te()
+                .get(type_argument.type_id)
+                .contains_never(engines),
+            TypeInfo::Unknown
+            | TypeInfo::UnknownGeneric { .. }
+            | TypeInfo::Placeholder(_)
+            | TypeInfo::TypeParam(_)
+            | TypeInfo::StringSlice
+            | TypeInfo::StringArray(_)
+            | TypeInfo::UnsignedInteger(_)
+            | TypeInfo::Enum(_)
+            | TypeInfo::Struct(_)
+            | TypeInfo::Boolean
+            | TypeInfo::ContractCaller { .. }
+            | TypeInfo::Custom { .. }
+            | TypeInfo::B256
+            | TypeInfo::Numeric
+            | TypeInfo::Contract
+            | TypeInfo::ErrorRecovery(_)
+            | TypeInfo::Storage { .. }
+            | TypeInfo::RawUntypedPtr
+            | TypeInfo::RawUntypedSlice
+            | TypeInfo::Ptr(_)
+            | TypeInfo::Slice(_)
+            | TypeInfo::Alias { .. }
+            | TypeInfo::TraitType { .. }
+            | TypeInfo::Ref { .. } => false,
+        }
+    }
+
     pub(crate) fn apply_type_arguments(
         self,
         handler: &Handler,

test/src/e2e_vm_tests/mod.rs

@@ -298,6 +298,8 @@ impl TestContext {
                     run_and_capture_output(|| harness::compile_to_bytes(&name, &run_config)).await;
                 *output = out;
 
+                check_file_checker(checker, &name, output)?;
+
                 let compiled = result?;
 
                 let compiled = match compiled {

test/src/e2e_vm_tests/test_programs/should_fail/return_in_strange_positions/src/main.sw

@@ -48,7 +48,7 @@ fn in_length_2_array_first() -> u64 {
 fn in_length_2_array_second() -> u64 {
     let _ = [0, return];
 
-    145 // TODO: Missing unreachable warning
+    145
 }
 
 fn in_tuple() -> u64 {

test/src/e2e_vm_tests/test_programs/should_pass/break_in_strange_positions/test.toml

@@ -1,4 +1,4 @@
 category = "run"
 expected_result = { action = "return", value = 8193 }
 validate_abi = true
-expected_warnings = 26
+expected_warnings = 33

test/src/e2e_vm_tests/test_programs/should_pass/continue_in_strange_positions/test.toml

@@ -1,4 +1,4 @@
 category = "run"
 expected_result = { action = "return", value = 8193 }
 validate_abi = true
-expected_warnings = 25
+expected_warnings = 31

test/src/e2e_vm_tests/test_programs/should_pass/language/diverging_exprs/test.toml

@@ -1,4 +1,4 @@
 category = "run"
 expected_result = { action = "return", value = 42 }
 validate_abi = true
-expected_warnings = 27
+expected_warnings = 31

test/src/e2e_vm_tests/test_programs/should_pass/language/implicit_casting/test.toml

@@ -2,10 +2,3 @@ category = "run"
 expected_result = { action = "return", value = 42 }
 validate_abi = true
 
-# check: let _a: Result<u32, u8> = Ok(5);
-# nextln: $()This cast, from integer type of width sixty four to integer type of width thirty two, will lose precision.
-
-# check: let _b: MyStruct<u32> = MyStruct{ a:5 };
-# nextln: $()This cast, from integer type of width sixty four to integer type of width thirty two, will lose precision.
-
-expected_warnings = 2

test/src/e2e_vm_tests/test_programs/should_pass/return_in_strange_positions/src/main.sw

@@ -20,34 +20,34 @@ pub enum Enum_multivariant {
 fn in_init() -> u64 {
     let _ = return 42;
 
-    45
+    045
 }
 
 fn in_array() -> u64 {
     let _ = [return 42, return 43];
 
-    145
+    1450
 }
 
 // Arrays of length 1 are treated differently
 fn in_length_1_array() -> u64 {
     let _ = [return 42];
 
-    145
+    1451
 }
 
 // The first element of an array is treated differently
 fn in_length_2_array_first() -> u64 {
     let _ = [return 42, 0];
 
-    145
+    1452
 }
 
 // The first element of an array is treated differently
 fn in_length_2_array_second() -> u64 {
     let _ = [0, return 42];
 
-    145 // TODO: Missing unreachable warning
+    1453
 }
 
 fn in_tuple() -> u64 {
@@ -90,19 +90,19 @@ fn in_while_condition() -> u64 {
         break;
     };
 
-    745 // TODO: Missing unreachable warning
+    745
 }
 
 fn in_enum() -> u64 {
     let _ = Enum::A((return 42, return 43));
 
-    845 // TODO: Missing unreachable warning
+    845
 }
 
 fn in_enum_multivariant() -> u64 {
     let _ = Enum_multivariant::B((return 42, return 43));
 
-    945 // TODO: Missing unreachable warning
+    945
 }
 
 fn helper_fun(x : u64, y : u64) -> u64 {
@@ -112,7 +112,7 @@ fn helper_fun(x : u64, y : u64) -> u64 {
 fn in_fun_arg() -> u64 {
     let _ = helper_fun(return 42, return 43);
 
-    1045 // TODO: Missing unreachable warning
+    1045
 }
 
 fn in_lazy_and() -> u64 {
@@ -128,11 +128,11 @@ fn in_lazy_or() -> u64 {
 }
 
 fn in_match_scrutinee() -> u64 {
-    match return 42 {
+    let _ = match return 42 {
         _ => 5411,
-    }
+    };
 
-    1145
+    1345
 }
 
 

test/src/e2e_vm_tests/test_programs/should_pass/return_in_strange_positions/test.toml

@@ -1,4 +1,67 @@
 category = "run"
 expected_result = { action = "return", value = 8193 }
 validate_abi = true
-expected_warnings = 17
+expected_warnings = 22
+
+#check: $()045
+#nextln: $()This code is unreachable.
+
+#check: $()1450
+#nextln: $()This code is unreachable.
+
+#check: $()1451
+#nextln: $()This code is unreachable.
+
+#check: $()1452
+#nextln: $()This code is unreachable.
+
+#check: $()1453
+#nextln: $()This code is unreachable.
+
+#check: $()245
+#nextln: $()This code is unreachable.
+
+#check: $()345
+#nextln: $()This code is unreachable.
+
+#check: $()445
+#nextln: $()This code is unreachable.
+
+#check: $()545
+#nextln: $()This code is unreachable.
+
+#check: $()543
+#nextln: $()This code is unreachable.
+
+#check: $()345
+#nextln: $()This code is unreachable.
+
+#check: $()645
+#nextln: $()This code is unreachable.
+
+# check: $()745
+# nextln: $()This code is unreachable.
+
+#check: $()845
+#nextln: $()This code is unreachable.
+
+#check: $()945
+#nextln: $()This code is unreachable.
+
+#check: $()1045
+#nextln: $()This code is unreachable.
+
+#check: $()1145
+#nextln: $()This code is unreachable.
+
+#check: $()1245
+#nextln: $()This code is unreachable.
+
+#check: $()let _ = match return 42 {
+#check: $()};
+#nextln: $()This code is unreachable.
+#nextln: $()
+#nextln: $()1345
+
+#check: $()1345
+#nextln: $()This code is unreachable.