Show code that caused unreachable code #2207

`$echo` would suppress warning about unreachable code. #2205

releasenotes.md

@@ -21,6 +21,7 @@
 - Add `--sources` build option to add additional files to compile. #2097
 - Support untyped second argument for operator overloading.
 - The form-feed character '\f' is no longer valid white space.
+- Show code that caused unreachable code #2207
 
 ### Fixes
 - `-2147483648`, MIN literals work correctly.
@@ -35,6 +36,7 @@
 - @operator macro using untyped parameter causes compiler segfault #2200.
 - Make `unreachable()` only panic in safe mode.
 - `cflags` additions for targets was not handed properly. #2209
+- `$echo` would suppress warning about unreachable code. #2205
 
 ### Stdlib changes
 - Deprecate `String.is_zstr` and `String.quick_zstr` #2188.

src/compiler/compiler_internal.h

@@ -1536,14 +1536,19 @@ typedef struct Module_
 } Module;
 
 
+typedef struct EndJump_
+{
+	bool active;
+	SourceSpan span;
+} EndJump;
 
 typedef struct DynamicScope_
 {
 	ScopeId scope_id;
 	bool allow_dead_code : 1;
-	bool jump_end : 1;
 	bool is_dead : 1;
 	bool is_invalid : 1;
+	EndJump end_jump;
 	ScopeFlags flags;
 	unsigned label_start;
 	unsigned current_local;

src/compiler/sema_expr.c

@@ -2627,13 +2627,13 @@ bool sema_expr_analyse_macro_call(SemaContext *context, Expr *call_expr, Expr *s
 	sema_append_contract_asserts(assert_first, body);
 	if (!sema_analyse_statement(&macro_context, body)) goto EXIT_FAIL;
 	ASSERT_SPAN(call_expr, macro_context.active_scope.depth == 1);
-	bool implicit_void_return = !macro_context.active_scope.jump_end;
+	bool implicit_void_return = !macro_context.active_scope.end_jump.active;
 	params = macro_context.macro_params;
 	bool is_no_return = sig->attrs.noreturn;
 
 	if (!vec_size(macro_context.returns))
 	{
-		if (rtype && rtype != type_void && !macro_context.active_scope.jump_end)
+		if (rtype && rtype != type_void && !macro_context.active_scope.end_jump.active)
 		{
 			SEMA_ERROR(decl,
 					   "Missing return in macro that should evaluate to %s.",
@@ -2730,7 +2730,7 @@ bool sema_expr_analyse_macro_call(SemaContext *context, Expr *call_expr, Expr *s
 	unsigned returns_found = vec_size(macro_context.returns);
 	// We may have zero normal macro returns but the active scope still has a "jump end".
 	// In this case it is triggered by the @body()
-	if (!returns_found && macro_context.active_scope.jump_end)
+	if (!returns_found && macro_context.active_scope.end_jump.active)
 	{
 		is_no_return = true;
 	}
@@ -2779,7 +2779,10 @@ EXIT:
 	}
 	ASSERT_SPAN(call_expr, context->active_scope.defer_last == context->active_scope.defer_start);
 	context->active_scope = old_scope;
-	if (is_no_return) context->active_scope.jump_end = true;
+	if (is_no_return)
+	{
+		SET_JUMP_END(context, call_expr);
+	}
 	sema_context_destroy(&macro_context);
 	call_expr->resolve_status = RESOLVE_DONE;
 	if (is_always_const && !expr_is_runtime_const(call_expr))
@@ -2893,9 +2896,9 @@ static bool sema_call_analyse_body_expansion(SemaContext *macro_context, Expr *c
 			return SCOPE_POP_ERROR();
 		}
 		ASSERT_SPAN(call, ast->ast_kind == AST_COMPOUND_STMT);
-		if (context->active_scope.jump_end)
+		if (context->active_scope.end_jump.active)
 		{
-			macro_context->active_scope.jump_end = true;
+			macro_context->active_scope.end_jump = context->active_scope.end_jump;
 		}
 		if (first_defer)
 		{
@@ -8573,7 +8576,7 @@ static inline bool sema_expr_analyse_or_error(SemaContext *context, Expr *expr,
 		RETURN_SEMA_ERROR(left, "No optional to use '\?\?' with, please remove the '\?\?'.");
 	}
 
-	bool active_scope_jump = context->active_scope.jump_end;
+	EndJump active_scope_jump = context->active_scope.end_jump;
 
 	// First we analyse the "else" and try to implictly cast.
 	if (!sema_analyse_inferred_expr(context, infer_type, right)) return false;
@@ -8585,7 +8588,7 @@ static inline bool sema_expr_analyse_or_error(SemaContext *context, Expr *expr,
 	}
 
 	// Ignore the jump here.
-	context->active_scope.jump_end = active_scope_jump;
+	context->active_scope.end_jump = active_scope_jump;
 
 	// Here we might need to insert casts.
 	Type *else_type = right->type;

src/compiler/sema_internal.h

@@ -41,6 +41,7 @@
 #define PUSH_BREAKCONT(ast) PUSH_CONTINUE(ast); PUSH_BREAK(ast)
 #define POP_BREAKCONT() POP_CONTINUE(); POP_BREAK()
 #define CHECK_ON_DEFINED(ref__) do { if (!ref__) break; *ref__ = true; return false; } while(0)
+#define SET_JUMP_END(context__, node__) do { (context__)->active_scope.end_jump = (EndJump) { true, (node__)->span }; } while(0)
 
 Decl **global_context_acquire_locals_list(void);
 void generic_context_release_locals_list(Decl **);

src/compiler/sema_stmts.c

@@ -161,14 +161,14 @@ static inline bool sema_analyse_assert_stmt(SemaContext *context, Ast *statement
 				// If this is a test, then assert(false) is permitted.
 				if (context->call_env.current_function && context->call_env.current_function->func_decl.attr_test)
 				{
-					context->active_scope.jump_end = true;
+					SET_JUMP_END(context, statement);
 					return true;
 				}
 				// Otherwise, require unreachable.
 				RETURN_SEMA_ERROR(expr, "Use 'unreachable' instead of 'assert(false)'.");
 			}
 			// Otherwise we print an error.
-			if (!context->active_scope.jump_end && !context->active_scope.is_dead)
+			if (!context->active_scope.end_jump.active && !context->active_scope.is_dead)
 			{
 				if (message_expr && sema_cast_const(message_expr) && vec_size(statement->assert_stmt.args))
 				{
@@ -212,7 +212,7 @@ static inline bool sema_analyse_break_stmt(SemaContext *context, Ast *statement)
 	}
 
 	// Is jump, and set it as resolved.
-	context->active_scope.jump_end = true;
+	SET_JUMP_END(context, statement);
 	statement->contbreak_stmt.is_resolved = true;
 
 	AstId defer_begin;
@@ -248,13 +248,13 @@ static inline bool sema_analyse_break_stmt(SemaContext *context, Ast *statement)
 static inline bool sema_analyse_compound_stmt(SemaContext *context, Ast *statement)
 {
 	bool success;
-	bool ends_with_jump;
+	EndJump ends_with_jump;
 	SCOPE_START
 		success = sema_analyse_compound_statement_no_scope(context, statement);
-		ends_with_jump = context->active_scope.jump_end;
+		ends_with_jump = context->active_scope.end_jump;
 	SCOPE_END;
 	// If this ends with a jump, then we know we don't need to certain analysis.
-	context->active_scope.jump_end = ends_with_jump;
+	context->active_scope.end_jump = ends_with_jump;
 	return success;
 }
 
@@ -313,7 +313,7 @@ static inline bool sema_analyse_continue_stmt(SemaContext *context, Ast *stateme
 	}
 
 	// This makes the active scope jump.
-	context->active_scope.jump_end = true;
+	SET_JUMP_END(context, statement);
 
 	// Link the parent and add the defers.
 	statement->contbreak_stmt.ast = astid(parent);
@@ -567,7 +567,7 @@ static inline bool sema_analyse_block_exit_stmt(SemaContext *context, Ast *state
 	bool is_macro = (context->active_scope.flags & SCOPE_MACRO) != 0;
 	ASSERT(context->active_scope.flags & SCOPE_MACRO);
 	statement->ast_kind = AST_BLOCK_EXIT_STMT;
-	context->active_scope.jump_end = true;
+	SET_JUMP_END(context, statement);
 	Type *block_type = context->expected_block_type;
 	Expr *ret_expr = statement->return_stmt.expr;
 	if (ret_expr)
@@ -680,7 +680,7 @@ static inline bool sema_analyse_return_stmt(SemaContext *context, Ast *statement
 	}
 
 	// 1. We mark that the current scope ends with a jump.
-	context->active_scope.jump_end = true;
+	SET_JUMP_END(context, statement);
 
 	Type *expected_rtype = context->rtype;
 	ASSERT(expected_rtype && "We should always have known type from a function return.");
@@ -1229,26 +1229,26 @@ static inline bool sema_analyse_expr_stmt(SemaContext *context, Ast *statement)
 		case EXPR_RETHROW:
 			if (expr->rethrow_expr.inner->expr_kind == EXPR_OPTIONAL)
 			{
-				context->active_scope.jump_end = true;
+				SET_JUMP_END(context, expr);
 			}
 			break;
 		case EXPR_FORCE_UNWRAP:
 			if (expr->inner_expr->expr_kind == EXPR_OPTIONAL)
 			{
-				context->active_scope.jump_end = true;
+				SET_JUMP_END(context, expr);
 			}
 			break;
 		case EXPR_POST_UNARY:
 			if (expr->rethrow_expr.inner->expr_kind == EXPR_OPTIONAL)
 			{
-				context->active_scope.jump_end = true;
+				SET_JUMP_END(context, expr);
 			}
 			break;
 		case EXPR_CALL:
-			if (expr->call_expr.no_return) context->active_scope.jump_end = true;
+			if (expr->call_expr.no_return) SET_JUMP_END(context, expr);
 			break;
 		case EXPR_MACRO_BLOCK:
-			if (expr->macro_block.is_noreturn) context->active_scope.jump_end = true;
+			if (expr->macro_block.is_noreturn) SET_JUMP_END(context, expr);
 			break;
 		case EXPR_CONST:
 			// Remove all const statements.
@@ -1385,7 +1385,7 @@ static inline bool sema_analyse_for_stmt(SemaContext *context, Ast *statement)
 
 			PUSH_BREAKCONT(statement);
 				success = sema_analyse_statement(context, body);
-				statement->for_stmt.flow.no_exit = context->active_scope.jump_end;
+				statement->for_stmt.flow.no_exit = context->active_scope.end_jump.active;
 			POP_BREAKCONT();
 
 			// End for body scope
@@ -1427,7 +1427,7 @@ static inline bool sema_analyse_for_stmt(SemaContext *context, Ast *statement)
 
 	if (is_infinite && !statement->for_stmt.flow.has_break)
 	{
-		context->active_scope.jump_end = true;
+		SET_JUMP_END(context, statement);
 	}
 	return success;
 }
@@ -1920,18 +1920,18 @@ static inline bool sema_analyse_if_stmt(SemaContext *context, Ast *statement)
 				success = false;
 			}
 		}
-		if (context->active_scope.jump_end && !context->active_scope.allow_dead_code)
+		if (context->active_scope.end_jump.active && !context->active_scope.allow_dead_code)
 		{
-			if (!SEMA_WARN(then, "This code will never execute."))
-			{
-				success = false;
-			}
+			context->active_scope.allow_dead_code = true;
+			bool warn = SEMA_WARN(statement, "This code will never execute.");
+			sema_note_prev_at(context->active_scope.end_jump.span, "This code is preventing it from exectuting");
+			if (!warn) return success = false;
 		}
 
 		SCOPE_START_WITH_LABEL(statement->if_stmt.flow.label);
 			if (result == COND_FALSE) context->active_scope.is_dead = true;
 			success = success && sema_analyse_statement(context, then);
-			then_jump = context->active_scope.jump_end;
+			then_jump = context->active_scope.end_jump.active;
 		SCOPE_END;
 
 		if (!success) goto END;
@@ -1943,7 +1943,7 @@ static inline bool sema_analyse_if_stmt(SemaContext *context, Ast *statement)
 				sema_remove_unwraps_from_try(context, cond);
 				sema_unwrappable_from_catch_in_else(context, cond);
 				success = success && sema_analyse_statement(context, else_body);
-				else_jump = context->active_scope.jump_end;
+				else_jump = context->active_scope.end_jump.active;
 			SCOPE_END;
 		}
 
@@ -1964,15 +1964,15 @@ END:
 	}
 	if (then_jump && else_jump && !statement->flow.has_break)
 	{
-		context->active_scope.jump_end = true;
+		SET_JUMP_END(context, statement);
 	}
 	else if (then_jump && result == COND_TRUE)
 	{
-		context->active_scope.jump_end = true;
+		SET_JUMP_END(context, statement);
 	}
 	else if (else_jump && result == COND_FALSE)
 	{
-		context->active_scope.jump_end = true;
+		SET_JUMP_END(context, statement);
 	}
 	return true;
 }
@@ -2070,7 +2070,7 @@ static bool context_labels_exist_in_scope(SemaContext *context)
 
 static bool sema_analyse_nextcase_stmt(SemaContext *context, Ast *statement)
 {
-	context->active_scope.jump_end = true;
+		SET_JUMP_END(context, statement);
 	if (!context->next_target && !statement->nextcase_stmt.label.name && !statement->nextcase_stmt.expr && !statement->nextcase_stmt.is_default)
 	{
 		if (context->next_switch)
@@ -2527,7 +2527,7 @@ static bool sema_analyse_switch_body(SemaContext *context, Ast *statement, Sourc
 			POP_BREAK();
 			POP_NEXT();
 			if (!body && i < case_count - 1) continue;
-			all_jump_end &= context->active_scope.jump_end;
+			all_jump_end &= context->active_scope.end_jump.active;
 		SCOPE_END;
 	}
 	if (is_enum_switch && !exhaustive && success)
@@ -2894,7 +2894,7 @@ static inline bool sema_analyse_switch_stmt(SemaContext *context, Ast *statement
 
 	if (statement->flow.no_exit && !statement->flow.has_break)
 	{
-		context->active_scope.jump_end = true;
+		SET_JUMP_END(context, statement);
 	}
 	return true;
 }
@@ -3108,21 +3108,20 @@ bool sema_analyse_statement(SemaContext *context, Ast *statement)
 {
 	if (context->active_scope.is_invalid) return false;
 	if (statement->ast_kind == AST_POISONED) return false;
-	bool dead_code = context->active_scope.jump_end;
+	EndJump end_jump = context->active_scope.end_jump;
 	unsigned returns = vec_size(context->returns);
 	if (!sema_analyse_statement_inner(context, statement)) return ast_poison(statement);
-	if (dead_code)
+	if (end_jump.active)
 	{
 		if (!context->active_scope.allow_dead_code)
 		{
-			context->active_scope.allow_dead_code = true;
 			// If we start with an don't start with an assert AND the scope is a macro, then it's bad.
 			if (statement->ast_kind != AST_ASSERT_STMT && statement->ast_kind != AST_NOP_STMT && !(context->active_scope.flags & SCOPE_MACRO))
 			{
-				if (!SEMA_WARN(statement, "This code will never execute."))
-				{
-					return ast_poison(statement);
-				}
+				context->active_scope.allow_dead_code = true;
+				bool warn = SEMA_WARN(statement, "This code will never execute.");
+				sema_note_prev_at(end_jump.span, "No code will execute after this statement.");
+				if (!warn) return ast_poison(statement);
 			}
 			// Remove it
 		}
@@ -3296,7 +3295,7 @@ bool sema_analyse_function_body(SemaContext *context, Decl *func)
 NEXT:
 		if (!sema_analyse_compound_statement_no_scope(context, body)) return false;
 		ASSERT_SPAN(func,context->active_scope.depth == 1);
-		if (!context->active_scope.jump_end)
+		if (!context->active_scope.end_jump.active)
 		{
 			if (canonical_rtype != type_void)
 			{

src/compiler/semantic_analyser.c

@@ -37,7 +37,6 @@ void context_change_scope_with_flags(SemaContext *context, ScopeFlags flags)
 	context->active_scope = (DynamicScope) {
 			.scope_id = ++context->scope_id,
 			.allow_dead_code = false,
-			.jump_end = false,
 			.is_dead = scope_is_dead,
 			.is_invalid = scope_is_invalid,
 			.depth = depth,
@@ -99,7 +98,7 @@ AstId context_get_defers(SemaContext *context, AstId defer_top, AstId defer_bott
 void context_pop_defers(SemaContext *context, AstId *next)
 {
 	AstId defer_start = context->active_scope.defer_start;
-	if (next && !context->active_scope.jump_end)
+	if (next && !context->active_scope.end_jump.active)
 	{
 		AstId defer_current = context->active_scope.defer_last;
 		while (defer_current != defer_start)

test/test_suite/functions/unreachable_code_trace.c3

@@ -0,0 +1,12 @@
+import std;
+
+macro something() {
+	unreachable("Hi there");
+}
+
+fn void main() {
+	something();
+
+	$echo "Hello";
+	io::printn("Hello, World"); // #warning: This code will never execute
+}