make it an error to ignore a statement's value

this makes {1;} an error.

src/analyze.cpp

@@ -2987,23 +2987,6 @@ void semantic_analyze(CodeGen *g) {
     }
 }
 
-bool is_node_void_expr(AstNode *node) {
-    if (node->type == NodeTypeContainerInitExpr &&
-        node->data.container_init_expr.kind == ContainerInitKindArray)
-    {
-        AstNode *type_node = node->data.container_init_expr.type;
-        if (type_node->type == NodeTypeSymbol &&
-            buf_eql_str(type_node->data.symbol_expr.symbol, "void"))
-        {
-            return true;
-        }
-    } else if (node->type == NodeTypeBlock && node->data.block.statements.length == 0) {
-        return true;
-    }
-
-    return false;
-}
-
 TypeTableEntry **get_int_type_ptr(CodeGen *g, bool is_signed, uint32_t size_in_bits) {
     size_t index;
     if (size_in_bits == 8) {

src/analyze.hpp

@@ -17,7 +17,6 @@ TypeTableEntry *new_type_table_entry(TypeTableEntryId id);
 TypeTableEntry *get_pointer_to_type(CodeGen *g, TypeTableEntry *child_type, bool is_const);
 TypeTableEntry *get_pointer_to_type_extra(CodeGen *g, TypeTableEntry *child_type, bool is_const,
         bool is_volatile, uint32_t bit_offset, uint32_t unaligned_bit_count);
-bool is_node_void_expr(AstNode *node);
 uint64_t type_size(CodeGen *g, TypeTableEntry *type_entry);
 uint64_t type_size_bits(CodeGen *g, TypeTableEntry *type_entry);
 TypeTableEntry **get_int_type_ptr(CodeGen *g, bool is_signed, uint32_t size_in_bits);

src/ir.cpp

@@ -3344,6 +3344,7 @@ static IrInstruction *ir_gen_block(IrBuilder *irb, Scope *parent_scope, AstNode
         return ir_mark_gen(ir_build_const_void(irb, child_scope, block_node));
     }
 
+    bool is_continuation_unreachable = false;
     IrInstruction *return_value = nullptr;
     for (size_t i = 0; i < block_node->data.block.statements.length; i += 1) {
         AstNode *statement_node = block_node->data.block.statements.at(i);
@@ -3367,7 +3368,7 @@ static IrInstruction *ir_gen_block(IrBuilder *irb, Scope *parent_scope, AstNode
                 scope_block->label_table.put(label_name, label);
             }
 
-            if (!(return_value && instr_is_unreachable(return_value))) {
+            if (!is_continuation_unreachable) {
                 // fall through into new labeled basic block
                 IrInstruction *is_comptime = ir_mark_gen(ir_build_const_bool(irb, child_scope, statement_node,
                         ir_should_inline(irb->exec, child_scope)));
@@ -3375,33 +3376,58 @@ static IrInstruction *ir_gen_block(IrBuilder *irb, Scope *parent_scope, AstNode
             }
             ir_set_cursor_at_end(irb, label_block);
 
-            return_value = nullptr;
+            // a label is an entry point
+            is_continuation_unreachable = false;
             continue;
         }
 
-        if (return_value && instr_is_unreachable(return_value)) {
+        if (is_continuation_unreachable) {
-            if (is_node_void_expr(statement_node))
+            // if you put a semicolon after a return statement,
+            // then we get a void statement in the unreachable area.
+            // this is fine. ignore any void blocks we get from this happening.
+            if (statement_node->type == NodeTypeBlock && statement_node->data.block.statements.length == 0)
                 continue;
             add_node_error(irb->codegen, statement_node, buf_sprintf("unreachable code"));
         }
 
-        return_value = ir_gen_node(irb, statement_node, child_scope);
+        IrInstruction *statement_value = ir_gen_node(irb, statement_node, child_scope);
-        if (statement_node->type == NodeTypeDefer && return_value != irb->codegen->invalid_instruction) {
+        is_continuation_unreachable = instr_is_unreachable(statement_value);
+        if (is_continuation_unreachable)
+            return_value = statement_value;
+        else
+            return_value = nullptr;
+        if (statement_node->type == NodeTypeDefer && statement_value != irb->codegen->invalid_instruction) {
             // defer starts a new scope
             child_scope = statement_node->data.defer.child_scope;
             assert(child_scope);
-        } else if (return_value->id == IrInstructionIdDeclVar) {
+        } else if (statement_value->id == IrInstructionIdDeclVar) {
             // variable declarations start a new scope
-            IrInstructionDeclVar *decl_var_instruction = (IrInstructionDeclVar *)return_value;
+            IrInstructionDeclVar *decl_var_instruction = (IrInstructionDeclVar *)statement_value;
             child_scope = decl_var_instruction->var->child_scope;
+        } else {
+            // label, defer, variable declaration will never be the last statement
+            if (i == block_node->data.block.statements.length - 1) {
+                // this is the result value statement
+                return_value = statement_value;
+            } else {
+                // there are more statements ahead of this one. this statement's value must be void
+                TypeTableEntry *instruction_type = statement_value->value.type;
+                if (instruction_type &&
+                    instruction_type->id != TypeTableEntryIdInvalid &&
+                    instruction_type->id != TypeTableEntryIdVoid &&
+                    instruction_type->id != TypeTableEntryIdUnreachable) {
+                    add_node_error(irb->codegen, statement_node, buf_sprintf("expression valued ignored"));
+                }
+            }
         }
     }
 
-    // labels are never the last statement
     assert(return_value != nullptr);
 
-    if (!instr_is_unreachable(return_value))
+    if (!is_continuation_unreachable) {
+        // control flow falls out of block
         ir_gen_defers_for_block(irb, child_scope, outer_block_scope, false, false);
+    }
 
     return return_value;
 }