add error for unused/duplicate block labels

lib/std/dwarf.zig

@@ -322,7 +322,7 @@ fn parseFormValue(allocator: *mem.Allocator, in_stream: anytype, form_id: u64, e
         FORM_block1 => parseFormValueBlock(allocator, in_stream, endian, 1),
         FORM_block2 => parseFormValueBlock(allocator, in_stream, endian, 2),
         FORM_block4 => parseFormValueBlock(allocator, in_stream, endian, 4),
-        FORM_block => x: {
+        FORM_block => {
             const block_len = try nosuspend leb.readULEB128(usize, in_stream);
             return parseFormValueBlockLen(allocator, in_stream, block_len);
         },

lib/std/special/c.zig

@@ -536,7 +536,7 @@ fn generic_fmod(comptime T: type, x: T, y: T) T {
     // normalize x and y
     if (ex == 0) {
         i = ux << exp_bits;
-        while (i >> bits_minus_1 == 0) : (b: {
+        while (i >> bits_minus_1 == 0) : ({
             ex -= 1;
             i <<= 1;
         }) {}
@@ -547,7 +547,7 @@ fn generic_fmod(comptime T: type, x: T, y: T) T {
     }
     if (ey == 0) {
         i = uy << exp_bits;
-        while (i >> bits_minus_1 == 0) : (b: {
+        while (i >> bits_minus_1 == 0) : ({
             ey -= 1;
             i <<= 1;
         }) {}
@@ -573,7 +573,7 @@ fn generic_fmod(comptime T: type, x: T, y: T) T {
             return 0 * x;
         ux = i;
     }
-    while (ux >> digits == 0) : (b: {
+    while (ux >> digits == 0) : ({
         ux <<= 1;
         ex -= 1;
     }) {}

lib/std/zig/render.zig

@@ -2385,7 +2385,7 @@ fn renderTokenOffset(
         }
     }
 
-    if (next_token_id != .LineComment) blk: {
+    if (next_token_id != .LineComment) {
         switch (space) {
             Space.None, Space.NoNewline => return,
             Space.Newline => {

src-self-hosted/translate_c.zig

@@ -931,7 +931,7 @@ fn transRecordDecl(c: *Context, record_decl: *const ZigClangRecordDecl) Error!?*
                 else => |e| return e,
             };
 
-            const align_expr = blk: {
+            const align_expr = blk_2: {
                 const alignment = ZigClangFieldDecl_getAlignedAttribute(field_decl, rp.c.clang_context);
                 if (alignment != 0) {
                     _ = try appendToken(rp.c, .Keyword_align, "align");
@@ -940,9 +940,9 @@ fn transRecordDecl(c: *Context, record_decl: *const ZigClangRecordDecl) Error!?*
                     const expr = try transCreateNodeInt(rp.c, alignment / 8);
                     _ = try appendToken(rp.c, .RParen, ")");
 
-                    break :blk expr;
+                    break :blk_2 expr;
                 }
-                break :blk null;
+                break :blk_2 null;
             };
 
             const field_node = try c.arena.create(ast.Node.ContainerField);
@@ -1073,9 +1073,9 @@ fn transEnumDecl(c: *Context, enum_decl: *const ZigClangEnumDecl) Error!?*ast.No
 
             const field_name_tok = try appendIdentifier(c, field_name);
 
-            const int_node = if (!pure_enum) blk: {
+            const int_node = if (!pure_enum) blk_2: {
                 _ = try appendToken(c, .Colon, "=");
-                break :blk try transCreateNodeAPInt(c, ZigClangEnumConstantDecl_getInitVal(enum_const));
+                break :blk_2 try transCreateNodeAPInt(c, ZigClangEnumConstantDecl_getInitVal(enum_const));
             } else
                 null;
 
@@ -2388,7 +2388,7 @@ fn transZeroInitExpr(
     ty: *const ZigClangType,
 ) TransError!*ast.Node {
     switch (ZigClangType_getTypeClass(ty)) {
-        .Builtin => blk: {
+        .Builtin => {
             const builtin_ty = @ptrCast(*const ZigClangBuiltinType, ty);
             switch (ZigClangBuiltinType_getKind(builtin_ty)) {
                 .Bool => return try transCreateNodeBoolLiteral(rp.c, false),

src/all_types.hpp

@@ -2438,6 +2438,7 @@ struct ScopeBlock {
     LVal lval;
     bool safety_off;
     bool fast_math_on;
+    bool name_used;
 };
 
 // This scope is created from every defer expression.
@@ -2488,6 +2489,8 @@ struct ScopeLoop {
     ZigList<IrBasicBlockSrc *> *incoming_blocks;
     ResultLocPeerParent *peer_parent;
     ScopeExpr *spill_scope;
+
+    bool name_used;
 };
 
 // This scope blocks certain things from working such as comptime continue

src/ir.cpp

@@ -5476,6 +5476,25 @@ static ResultLocPeer *create_peer_result(ResultLocPeerParent *peer_parent) {
     return result;
 }
 
+static bool is_duplicate_label(CodeGen *g, Scope *scope, AstNode *node, Buf *name) {
+    if (name == nullptr) return false;
+
+    for (;;) {
+        if (scope == nullptr || scope->id == ScopeIdFnDef) {
+            break;
+        } else if (scope->id == ScopeIdBlock || scope->id == ScopeIdLoop) {
+            Buf *this_block_name = scope->id == ScopeIdBlock ? ((ScopeBlock *)scope)->name : ((ScopeLoop *)scope)->name;
+            if (this_block_name != nullptr && buf_eql_buf(name, this_block_name)) {
+                ErrorMsg *msg = add_node_error(g, node, buf_sprintf("redeclaration of label '%s'", buf_ptr(name)));
+                add_error_note(g, msg, scope->source_node, buf_sprintf("previous declaration is here"));
+                return true;
+            }
+        }
+        scope = scope->parent;
+    }
+    return false;
+}
+
 static IrInstSrc *ir_gen_block(IrBuilderSrc *irb, Scope *parent_scope, AstNode *block_node, LVal lval,
         ResultLoc *result_loc)
 {
@@ -5484,6 +5503,9 @@ static IrInstSrc *ir_gen_block(IrBuilderSrc *irb, Scope *parent_scope, AstNode *
     ZigList<IrInstSrc *> incoming_values = {0};
     ZigList<IrBasicBlockSrc *> incoming_blocks = {0};
 
+    if (is_duplicate_label(irb->codegen, parent_scope, block_node, block_node->data.block.name))
+        return irb->codegen->invalid_inst_src;
+
     ScopeBlock *scope_block = create_block_scope(irb->codegen, block_node, parent_scope);
 
     Scope *outer_block_scope = &scope_block->base;
@@ -5495,6 +5517,9 @@ static IrInstSrc *ir_gen_block(IrBuilderSrc *irb, Scope *parent_scope, AstNode *
     }
 
     if (block_node->data.block.statements.length == 0) {
+        if (scope_block->name != nullptr) {
+            add_node_error(irb->codegen, block_node, buf_sprintf("unused block label"));
+        }
         // {}
         return ir_lval_wrap(irb, parent_scope, ir_build_const_void(irb, child_scope, block_node), lval, result_loc);
     }
@@ -5552,6 +5577,10 @@ static IrInstSrc *ir_gen_block(IrBuilderSrc *irb, Scope *parent_scope, AstNode *
         }
     }
 
+    if (scope_block->name != nullptr && scope_block->name_used == false) {
+        add_node_error(irb->codegen, block_node, buf_sprintf("unused block label"));
+    }
+
     if (found_invalid_inst)
         return irb->codegen->invalid_inst_src;
 
@@ -8152,6 +8181,9 @@ static IrInstSrc *ir_gen_while_expr(IrBuilderSrc *irb, Scope *scope, AstNode *no
         ZigList<IrInstSrc *> incoming_values = {0};
         ZigList<IrBasicBlockSrc *> incoming_blocks = {0};
 
+        if (is_duplicate_label(irb->codegen, payload_scope, node, node->data.while_expr.name))
+            return irb->codegen->invalid_inst_src;
+
         ScopeLoop *loop_scope = create_loop_scope(irb->codegen, node, payload_scope);
         loop_scope->break_block = end_block;
         loop_scope->continue_block = continue_block;
@@ -8169,6 +8201,10 @@ static IrInstSrc *ir_gen_while_expr(IrBuilderSrc *irb, Scope *scope, AstNode *no
         if (body_result == irb->codegen->invalid_inst_src)
             return body_result;
 
+        if (loop_scope->name != nullptr && loop_scope->name_used == false) {
+            add_node_error(irb->codegen, node, buf_sprintf("unused while label"));
+        }
+
         if (!instr_is_unreachable(body_result)) {
             ir_mark_gen(ir_build_check_statement_is_void(irb, payload_scope, node->data.while_expr.body, body_result));
             ir_mark_gen(ir_build_br(irb, payload_scope, node, continue_block, is_comptime));
@@ -8263,6 +8299,9 @@ static IrInstSrc *ir_gen_while_expr(IrBuilderSrc *irb, Scope *scope, AstNode *no
         ZigList<IrInstSrc *> incoming_values = {0};
         ZigList<IrBasicBlockSrc *> incoming_blocks = {0};
 
+        if (is_duplicate_label(irb->codegen, child_scope, node, node->data.while_expr.name))
+            return irb->codegen->invalid_inst_src;
+
         ScopeLoop *loop_scope = create_loop_scope(irb->codegen, node, child_scope);
         loop_scope->break_block = end_block;
         loop_scope->continue_block = continue_block;
@@ -8280,6 +8319,10 @@ static IrInstSrc *ir_gen_while_expr(IrBuilderSrc *irb, Scope *scope, AstNode *no
         if (body_result == irb->codegen->invalid_inst_src)
             return body_result;
 
+        if (loop_scope->name != nullptr && loop_scope->name_used == false) {
+            add_node_error(irb->codegen, node, buf_sprintf("unused while label"));
+        }
+
         if (!instr_is_unreachable(body_result)) {
             ir_mark_gen(ir_build_check_statement_is_void(irb, child_scope, node->data.while_expr.body, body_result));
             ir_mark_gen(ir_build_br(irb, child_scope, node, continue_block, is_comptime));
@@ -8353,6 +8396,9 @@ static IrInstSrc *ir_gen_while_expr(IrBuilderSrc *irb, Scope *scope, AstNode *no
 
         Scope *subexpr_scope = create_runtime_scope(irb->codegen, node, scope, is_comptime);
 
+        if (is_duplicate_label(irb->codegen, subexpr_scope, node, node->data.while_expr.name))
+            return irb->codegen->invalid_inst_src;
+
         ScopeLoop *loop_scope = create_loop_scope(irb->codegen, node, subexpr_scope);
         loop_scope->break_block = end_block;
         loop_scope->continue_block = continue_block;
@@ -8369,6 +8415,10 @@ static IrInstSrc *ir_gen_while_expr(IrBuilderSrc *irb, Scope *scope, AstNode *no
         if (body_result == irb->codegen->invalid_inst_src)
             return body_result;
 
+        if (loop_scope->name != nullptr && loop_scope->name_used == false) {
+            add_node_error(irb->codegen, node, buf_sprintf("unused while label"));
+        }
+
         if (!instr_is_unreachable(body_result)) {
             ir_mark_gen(ir_build_check_statement_is_void(irb, scope, node->data.while_expr.body, body_result));
             ir_mark_gen(ir_build_br(irb, scope, node, continue_block, is_comptime));
@@ -8501,6 +8551,9 @@ static IrInstSrc *ir_gen_for_expr(IrBuilderSrc *irb, Scope *parent_scope, AstNod
         elem_ptr : ir_build_load_ptr(irb, &spill_scope->base, elem_node, elem_ptr);
     build_decl_var_and_init(irb, parent_scope, elem_node, elem_var, elem_value, buf_ptr(elem_var_name), is_comptime);
 
+    if (is_duplicate_label(irb->codegen, child_scope, node, node->data.for_expr.name))
+        return irb->codegen->invalid_inst_src;
+    
     ZigList<IrInstSrc *> incoming_values = {0};
     ZigList<IrBasicBlockSrc *> incoming_blocks = {0};
     ScopeLoop *loop_scope = create_loop_scope(irb->codegen, node, child_scope);
@@ -8520,6 +8573,10 @@ static IrInstSrc *ir_gen_for_expr(IrBuilderSrc *irb, Scope *parent_scope, AstNod
     if (body_result == irb->codegen->invalid_inst_src)
         return irb->codegen->invalid_inst_src;
 
+    if (loop_scope->name != nullptr && loop_scope->name_used == false) {
+        add_node_error(irb->codegen, node, buf_sprintf("unused for label"));
+    }
+
     if (!instr_is_unreachable(body_result)) {
         ir_mark_gen(ir_build_check_statement_is_void(irb, child_scope, node->data.for_expr.body, body_result));
         ir_mark_gen(ir_build_br(irb, child_scope, node, continue_block, is_comptime));
@@ -9464,6 +9521,7 @@ static IrInstSrc *ir_gen_break(IrBuilderSrc *irb, Scope *break_scope, AstNode *n
             if (node->data.break_expr.name == nullptr ||
                 (this_loop_scope->name != nullptr && buf_eql_buf(node->data.break_expr.name, this_loop_scope->name)))
             {
+                this_loop_scope->name_used = true;
                 loop_scope = this_loop_scope;
                 break;
             }
@@ -9473,6 +9531,7 @@ static IrInstSrc *ir_gen_break(IrBuilderSrc *irb, Scope *break_scope, AstNode *n
                 (this_block_scope->name != nullptr && buf_eql_buf(node->data.break_expr.name, this_block_scope->name)))
             {
                 assert(this_block_scope->end_block != nullptr);
+                this_block_scope->name_used = true;
                 return ir_gen_return_from_block(irb, break_scope, node, this_block_scope);
             }
         } else if (search_scope->id == ScopeIdSuspend) {
@@ -9540,6 +9599,7 @@ static IrInstSrc *ir_gen_continue(IrBuilderSrc *irb, Scope *continue_scope, AstN
             if (node->data.continue_expr.name == nullptr ||
                 (this_loop_scope->name != nullptr && buf_eql_buf(node->data.continue_expr.name, this_loop_scope->name)))
             {
+                this_loop_scope->name_used = true;
                 loop_scope = this_loop_scope;
                 break;
             }

test/compile_errors.zig

@@ -2,6 +2,29 @@ const tests = @import("tests.zig");
 const std = @import("std");
 
 pub fn addCases(cases: *tests.CompileErrorContext) void {
+    cases.addTest("duplicate/unused labels",
+        \\comptime {
+        \\    blk: { blk: while (false) {} }
+        \\    blk: while (false) { blk: for (@as([0]void, undefined)) |_| {} }
+        \\    blk: for (@as([0]void, undefined)) |_| { blk: {} }
+        \\}
+        \\comptime {
+        \\    blk: {}
+        \\    blk: while(false) {}
+        \\    blk: for(@as([0]void, undefined)) |_| {}
+        \\}
+    , &[_][]const u8{
+        "tmp.zig:2:17: error: redeclaration of label 'blk'",
+        "tmp.zig:2:10: note: previous declaration is here",
+        "tmp.zig:3:31: error: redeclaration of label 'blk'",
+        "tmp.zig:3:10: note: previous declaration is here",
+        "tmp.zig:4:51: error: redeclaration of label 'blk'",
+        "tmp.zig:4:10: note: previous declaration is here",
+        "tmp.zig:7:10: error: unused block label",
+        "tmp.zig:8:10: error: unused while label",
+        "tmp.zig:9:10: error: unused for label",
+    });
+
     cases.addTest("@alignCast of zero sized types",
         \\export fn foo() void {
         \\    const a: *void = undefined;