Commit 8fd0fddce5

Andrew Kelley <superjoe30@gmail.com>
2017-04-03 00:19:59
zig build system progress
* In-progress os.ChildProcess.spawn implementation. See #204 * Add explicit cast from integer to error. Closes #294 * fix casting from error to integer * fix compiler crash when initializing variable to undefined with no type
1 parent 0594487
src/all_types.hpp
@@ -520,7 +520,6 @@ struct AstNodeUnwrapErrorExpr {
 enum CastOp {
     CastOpNoCast, // signifies the function call expression is not a cast
     CastOpNoop, // fn call expr is a cast, but does nothing
-    CastOpErrToInt,
     CastOpIntToFloat,
     CastOpFloatToInt,
     CastOpBoolToInt,
@@ -1223,6 +1222,7 @@ enum PanicMsgId {
     PanicMsgIdSliceWidenRemainder,
     PanicMsgIdUnwrapMaybeFail,
     PanicMsgIdUnwrapErrFail,
+    PanicMsgIdInvalidErrorCode,
 
     PanicMsgIdCount,
 };
@@ -1728,6 +1728,8 @@ enum IrInstructionId {
     IrInstructionIdIntToPtr,
     IrInstructionIdPtrToInt,
     IrInstructionIdIntToEnum,
+    IrInstructionIdIntToErr,
+    IrInstructionIdErrToInt,
     IrInstructionIdCheckSwitchProngs,
     IrInstructionIdTestType,
     IrInstructionIdTypeName,
@@ -2404,6 +2406,18 @@ struct IrInstructionIntToEnum {
     IrInstruction *target;
 };
 
+struct IrInstructionIntToErr {
+    IrInstruction base;
+
+    IrInstruction *target;
+};
+
+struct IrInstructionErrToInt {
+    IrInstruction base;
+
+    IrInstruction *target;
+};
+
 struct IrInstructionCheckSwitchProngsRange {
     IrInstruction *start;
     IrInstruction *end;
src/codegen.cpp
@@ -570,6 +570,8 @@ static Buf *panic_msg_buf(PanicMsgId msg_id) {
             return buf_create_from_str("attempt to unwrap error");
         case PanicMsgIdUnreachable:
             return buf_create_from_str("reached unreachable code");
+        case PanicMsgIdInvalidErrorCode:
+            return buf_create_from_str("invalid error code");
     }
     zig_unreachable();
 }
@@ -1227,14 +1229,6 @@ static LLVMValueRef ir_render_cast(CodeGen *g, IrExecutable *executable,
             zig_unreachable();
         case CastOpNoop:
             return expr_val;
-        case CastOpErrToInt:
-            assert(actual_type->id == TypeTableEntryIdErrorUnion);
-            if (!type_has_bits(actual_type->data.error.child_type)) {
-                return gen_widen_or_shorten(g, ir_want_debug_safety(g, &cast_instruction->base),
-                    g->err_tag_type, wanted_type, expr_val);
-            } else {
-                zig_panic("TODO");
-            }
         case CastOpResizeSlice:
             {
                 assert(cast_instruction->tmp_ptr);
@@ -1402,6 +1396,66 @@ static LLVMValueRef ir_render_int_to_enum(CodeGen *g, IrExecutable *executable,
             instruction->target->value.type, wanted_int_type, target_val);
 }
 
+static LLVMValueRef ir_render_int_to_err(CodeGen *g, IrExecutable *executable, IrInstructionIntToErr *instruction) {
+    TypeTableEntry *wanted_type = instruction->base.value.type;
+    assert(wanted_type->id == TypeTableEntryIdPureError);
+
+    TypeTableEntry *actual_type = instruction->target->value.type;
+    assert(actual_type->id == TypeTableEntryIdInt);
+    assert(!actual_type->data.integral.is_signed);
+
+    LLVMValueRef target_val = ir_llvm_value(g, instruction->target);
+
+    if (ir_want_debug_safety(g, &instruction->base)) {
+        LLVMValueRef zero = LLVMConstNull(actual_type->type_ref);
+        LLVMValueRef neq_zero_bit = LLVMBuildICmp(g->builder, LLVMIntNE, target_val, zero, "");
+        LLVMValueRef ok_bit;
+        uint64_t biggest_possible_err_val = max_unsigned_val(actual_type);
+        if (biggest_possible_err_val < g->error_decls.length) {
+            ok_bit = neq_zero_bit;
+        } else {
+            LLVMValueRef error_value_count = LLVMConstInt(actual_type->type_ref, g->error_decls.length, false);
+            LLVMValueRef in_bounds_bit = LLVMBuildICmp(g->builder, LLVMIntULT, target_val, error_value_count, "");
+            ok_bit = LLVMBuildAnd(g->builder, neq_zero_bit, in_bounds_bit, "");
+        }
+
+        LLVMBasicBlockRef ok_block = LLVMAppendBasicBlock(g->cur_fn_val, "IntToErrOk");
+        LLVMBasicBlockRef fail_block = LLVMAppendBasicBlock(g->cur_fn_val, "IntToErrFail");
+
+        LLVMBuildCondBr(g->builder, ok_bit, ok_block, fail_block);
+
+        LLVMPositionBuilderAtEnd(g->builder, fail_block);
+        gen_debug_safety_crash(g, PanicMsgIdInvalidErrorCode);
+
+        LLVMPositionBuilderAtEnd(g->builder, ok_block);
+    }
+
+    return gen_widen_or_shorten(g, false, actual_type, g->err_tag_type, target_val);
+}
+
+static LLVMValueRef ir_render_err_to_int(CodeGen *g, IrExecutable *executable, IrInstructionErrToInt *instruction) {
+    TypeTableEntry *wanted_type = instruction->base.value.type;
+    assert(wanted_type->id == TypeTableEntryIdInt);
+    assert(!wanted_type->data.integral.is_signed);
+
+    TypeTableEntry *actual_type = instruction->target->value.type;
+    LLVMValueRef target_val = ir_llvm_value(g, instruction->target);
+
+    if (actual_type->id == TypeTableEntryIdPureError) {
+        return gen_widen_or_shorten(g, ir_want_debug_safety(g, &instruction->base),
+            g->err_tag_type, wanted_type, target_val);
+    } else if (actual_type->id == TypeTableEntryIdErrorUnion) {
+        if (!type_has_bits(actual_type->data.error.child_type)) {
+            return gen_widen_or_shorten(g, ir_want_debug_safety(g, &instruction->base),
+                g->err_tag_type, wanted_type, target_val);
+        } else {
+            zig_panic("TODO");
+        }
+    } else {
+        zig_unreachable();
+    }
+}
+
 static LLVMValueRef ir_render_unreachable(CodeGen *g, IrExecutable *executable,
         IrInstructionUnreachable *unreachable_instruction)
 {
@@ -2786,6 +2840,10 @@ static LLVMValueRef ir_render_instruction(CodeGen *g, IrExecutable *executable,
             return ir_render_int_to_ptr(g, executable, (IrInstructionIntToPtr *)instruction);
         case IrInstructionIdIntToEnum:
             return ir_render_int_to_enum(g, executable, (IrInstructionIntToEnum *)instruction);
+        case IrInstructionIdIntToErr:
+            return ir_render_int_to_err(g, executable, (IrInstructionIntToErr *)instruction);
+        case IrInstructionIdErrToInt:
+            return ir_render_err_to_int(g, executable, (IrInstructionErrToInt *)instruction);
         case IrInstructionIdContainerInitList:
             return ir_render_container_init_list(g, executable, (IrInstructionContainerInitList *)instruction);
         case IrInstructionIdPanic:
src/ir.cpp
@@ -500,6 +500,14 @@ static constexpr IrInstructionId ir_instruction_id(IrInstructionIntToEnum *) {
     return IrInstructionIdIntToEnum;
 }
 
+static constexpr IrInstructionId ir_instruction_id(IrInstructionIntToErr *) {
+    return IrInstructionIdIntToErr;
+}
+
+static constexpr IrInstructionId ir_instruction_id(IrInstructionErrToInt *) {
+    return IrInstructionIdErrToInt;
+}
+
 static constexpr IrInstructionId ir_instruction_id(IrInstructionCheckSwitchProngs *) {
     return IrInstructionIdCheckSwitchProngs;
 }
@@ -2002,6 +2010,30 @@ static IrInstruction *ir_build_int_to_enum(IrBuilder *irb, Scope *scope, AstNode
     return &instruction->base;
 }
 
+static IrInstruction *ir_build_int_to_err(IrBuilder *irb, Scope *scope, AstNode *source_node,
+        IrInstruction *target)
+{
+    IrInstructionIntToErr *instruction = ir_build_instruction<IrInstructionIntToErr>(
+            irb, scope, source_node);
+    instruction->target = target;
+
+    ir_ref_instruction(target, irb->current_basic_block);
+
+    return &instruction->base;
+}
+
+static IrInstruction *ir_build_err_to_int(IrBuilder *irb, Scope *scope, AstNode *source_node,
+        IrInstruction *target)
+{
+    IrInstructionErrToInt *instruction = ir_build_instruction<IrInstructionErrToInt>(
+            irb, scope, source_node);
+    instruction->target = target;
+
+    ir_ref_instruction(target, irb->current_basic_block);
+
+    return &instruction->base;
+}
+
 static IrInstruction *ir_build_check_switch_prongs(IrBuilder *irb, Scope *scope, AstNode *source_node,
         IrInstruction *target_value, IrInstructionCheckSwitchProngsRange *ranges, size_t range_count)
 {
@@ -2704,6 +2736,20 @@ static IrInstruction *ir_instruction_inttoenum_get_dep(IrInstructionIntToEnum *i
     }
 }
 
+static IrInstruction *ir_instruction_inttoerr_get_dep(IrInstructionIntToErr *instruction, size_t index) {
+    switch (index) {
+        case 0: return instruction->target;
+        default: return nullptr;
+    }
+}
+
+static IrInstruction *ir_instruction_errtoint_get_dep(IrInstructionErrToInt *instruction, size_t index) {
+    switch (index) {
+        case 0: return instruction->target;
+        default: return nullptr;
+    }
+}
+
 static IrInstruction *ir_instruction_checkswitchprongs_get_dep(IrInstructionCheckSwitchProngs *instruction,
         size_t index)
 {
@@ -2938,6 +2984,10 @@ static IrInstruction *ir_instruction_get_dep(IrInstruction *instruction, size_t
             return ir_instruction_ptrtoint_get_dep((IrInstructionPtrToInt *) instruction, index);
         case IrInstructionIdIntToEnum:
             return ir_instruction_inttoenum_get_dep((IrInstructionIntToEnum *) instruction, index);
+        case IrInstructionIdIntToErr:
+            return ir_instruction_inttoerr_get_dep((IrInstructionIntToErr *) instruction, index);
+        case IrInstructionIdErrToInt:
+            return ir_instruction_errtoint_get_dep((IrInstructionErrToInt *) instruction, index);
         case IrInstructionIdCheckSwitchProngs:
             return ir_instruction_checkswitchprongs_get_dep((IrInstructionCheckSwitchProngs *) instruction, index);
         case IrInstructionIdTestType:
@@ -6001,20 +6051,6 @@ static void eval_const_expr_implicit_cast(CastOp cast_op,
         case CastOpBytesToSlice:
             // can't do it
             break;
-        case CastOpErrToInt:
-            {
-                uint64_t value;
-                if (other_type->id == TypeTableEntryIdErrorUnion) {
-                    value = other_val->data.x_err_union.err ? other_val->data.x_err_union.err->value : 0;
-                } else if (other_type->id == TypeTableEntryIdPureError) {
-                    value = other_val->data.x_pure_err->value;
-                } else {
-                    zig_unreachable();
-                }
-                bignum_init_unsigned(&const_val->data.x_bignum, value);
-                const_val->special = ConstValSpecialStatic;
-                break;
-            }
         case CastOpIntToFloat:
             bignum_cast_to_float(&const_val->data.x_bignum, &other_val->data.x_bignum);
             const_val->special = ConstValSpecialStatic;
@@ -6707,6 +6743,87 @@ static IrInstruction *ir_analyze_number_to_literal(IrAnalyze *ira, IrInstruction
     return result;
 }
 
+static IrInstruction *ir_analyze_int_to_err(IrAnalyze *ira, IrInstruction *source_instr, IrInstruction *target) {
+    assert(target->value.type->id == TypeTableEntryIdInt);
+    assert(!target->value.type->data.integral.is_signed);
+
+    if (instr_is_comptime(target)) {
+        ConstExprValue *val = ir_resolve_const(ira, target, UndefBad);
+        if (!val)
+            return ira->codegen->invalid_instruction;
+
+        IrInstruction *result = ir_create_const(&ira->new_irb, source_instr->scope,
+                source_instr->source_node, ira->codegen->builtin_types.entry_pure_error);
+
+        uint64_t index = val->data.x_bignum.data.x_uint;
+        if (index == 0 || index >= ira->codegen->error_decls.length) {
+            ir_add_error(ira, source_instr,
+                buf_sprintf("integer value %" PRIu64 " represents no error", index));
+            return ira->codegen->invalid_instruction;
+        }
+
+        AstNode *error_decl_node = ira->codegen->error_decls.at(index);
+        result->value.data.x_pure_err = error_decl_node->data.error_value_decl.err;
+        return result;
+    }
+
+    IrInstruction *result = ir_build_int_to_err(&ira->new_irb, source_instr->scope, source_instr->source_node, target);
+    result->value.type = ira->codegen->builtin_types.entry_pure_error;
+    return result;
+}
+
+static IrInstruction *ir_analyze_err_to_int(IrAnalyze *ira, IrInstruction *source_instr, IrInstruction *target,
+        TypeTableEntry *wanted_type)
+{
+    assert(wanted_type->id == TypeTableEntryIdInt);
+
+    TypeTableEntry *err_type = target->value.type;
+
+    if (instr_is_comptime(target)) {
+        ConstExprValue *val = ir_resolve_const(ira, target, UndefBad);
+        if (!val)
+            return ira->codegen->invalid_instruction;
+
+        IrInstruction *result = ir_create_const(&ira->new_irb, source_instr->scope,
+                source_instr->source_node, wanted_type);
+
+        ErrorTableEntry *err;
+        if (err_type->id == TypeTableEntryIdErrorUnion) {
+            err = val->data.x_err_union.err;
+        } else if (err_type->id == TypeTableEntryIdPureError) {
+            err = val->data.x_pure_err;
+        } else {
+            zig_unreachable();
+        }
+        result->value.type = wanted_type;
+        uint64_t err_value = err ? err->value : 0;
+        bignum_init_unsigned(&result->value.data.x_bignum, err_value);
+
+        if (!bignum_fits_in_bits(&result->value.data.x_bignum,
+            wanted_type->data.integral.bit_count, wanted_type->data.integral.is_signed))
+        {
+            ir_add_error_node(ira, source_instr->source_node,
+                    buf_sprintf("error code '%s' does not fit in '%s'",
+                        buf_ptr(&err->name), buf_ptr(&wanted_type->name)));
+            return ira->codegen->invalid_instruction;
+        }
+
+        return result;
+    }
+
+    BigNum bn;
+    bignum_init_unsigned(&bn, ira->codegen->error_decls.length);
+    if (!bignum_fits_in_bits(&bn, wanted_type->data.integral.bit_count, wanted_type->data.integral.is_signed)) {
+        ir_add_error_node(ira, source_instr->source_node,
+                buf_sprintf("too many error values to fit in '%s'", buf_ptr(&wanted_type->name)));
+        return ira->codegen->invalid_instruction;
+    }
+
+    IrInstruction *result = ir_build_err_to_int(&ira->new_irb, source_instr->scope, source_instr->source_node, target);
+    result->value.type = wanted_type;
+    return result;
+}
+
 static IrInstruction *ir_analyze_cast(IrAnalyze *ira, IrInstruction *source_instr,
     TypeTableEntry *wanted_type, IrInstruction *value)
 {
@@ -6781,7 +6898,7 @@ static IrInstruction *ir_analyze_cast(IrAnalyze *ira, IrInstruction *source_inst
         return ir_resolve_cast(ira, source_instr, value, wanted_type, CastOpFloatToInt, false);
     }
 
-    // explicit cast from array to slice
+    // explicit cast from [N]T to []const T
     if (is_slice(wanted_type) && actual_type->id == TypeTableEntryIdArray) {
         TypeTableEntry *ptr_type = wanted_type->data.structure.fields[slice_ptr_index].type_entry;
         assert(ptr_type->id == TypeTableEntryIdPointer);
@@ -6909,17 +7026,14 @@ static IrInstruction *ir_analyze_cast(IrAnalyze *ira, IrInstruction *source_inst
     if ((actual_type_is_void_err || actual_type_is_pure_err) &&
         wanted_type->id == TypeTableEntryIdInt)
     {
-        BigNum bn;
-        bignum_init_unsigned(&bn, ira->codegen->error_decls.length);
-        if (bignum_fits_in_bits(&bn, wanted_type->data.integral.bit_count,
-                    wanted_type->data.integral.is_signed))
-        {
-            return ir_resolve_cast(ira, source_instr, value, wanted_type, CastOpErrToInt, false);
-        } else {
-            ir_add_error_node(ira, source_instr->source_node,
-                    buf_sprintf("too many error values to fit in '%s'", buf_ptr(&wanted_type->name)));
-            return ira->codegen->invalid_instruction;
-        }
+        return ir_analyze_err_to_int(ira, source_instr, value, wanted_type);
+    }
+
+    // explicit cast from integer to pure error
+    if (wanted_type->id == TypeTableEntryIdPureError && actual_type->id == TypeTableEntryIdInt &&
+        !actual_type->data.integral.is_signed)
+    {
+        return ir_analyze_int_to_err(ira, source_instr, value);
     }
 
     // explicit cast from integer to enum type with no payload
@@ -7843,7 +7957,7 @@ static TypeTableEntry *ir_analyze_instruction_decl_var(IrAnalyze *ira, IrInstruc
         result_type = ira->codegen->builtin_types.entry_invalid;
     }
 
-    bool is_comptime_var = ir_get_var_is_comptime(var); 
+    bool is_comptime_var = ir_get_var_is_comptime(var);
 
     switch (result_type->id) {
         case TypeTableEntryIdTypeDecl:
@@ -7852,6 +7966,7 @@ static TypeTableEntry *ir_analyze_instruction_decl_var(IrAnalyze *ira, IrInstruc
             break; // handled above
         case TypeTableEntryIdNumLitFloat:
         case TypeTableEntryIdNumLitInt:
+        case TypeTableEntryIdUndefLit:
             if (is_export || is_extern || (!var->src_is_const && !is_comptime_var)) {
                 ir_add_error_node(ira, source_node, buf_sprintf("unable to infer variable type"));
                 result_type = ira->codegen->builtin_types.entry_invalid;
@@ -7873,7 +7988,6 @@ static TypeTableEntry *ir_analyze_instruction_decl_var(IrAnalyze *ira, IrInstruc
                 result_type = ira->codegen->builtin_types.entry_invalid;
             }
             break;
-        case TypeTableEntryIdUndefLit:
         case TypeTableEntryIdVoid:
         case TypeTableEntryIdBool:
         case TypeTableEntryIdInt:
@@ -10765,6 +10879,8 @@ static TypeTableEntry *ir_analyze_instruction_container_init_list(IrAnalyze *ira
         TypeTableEntry *this_field_type = field->type_entry;
 
         IrInstruction *init_value = instruction->items[0]->other;
+        if (type_is_invalid(init_value->value.type))
+            return ira->codegen->builtin_types.entry_invalid;
 
         IrInstruction *casted_init_value = ir_implicit_cast(ira, init_value, this_field_type);
         if (casted_init_value == ira->codegen->invalid_instruction)
@@ -12311,6 +12427,8 @@ static TypeTableEntry *ir_analyze_instruction_nocast(IrAnalyze *ira, IrInstructi
         case IrInstructionIdIntToPtr:
         case IrInstructionIdPtrToInt:
         case IrInstructionIdIntToEnum:
+        case IrInstructionIdIntToErr:
+        case IrInstructionIdErrToInt:
         case IrInstructionIdStructInit:
         case IrInstructionIdStructFieldPtr:
         case IrInstructionIdEnumFieldPtr:
@@ -12650,6 +12768,8 @@ bool ir_has_side_effects(IrInstruction *instruction) {
         case IrInstructionIdPtrToInt:
         case IrInstructionIdIntToPtr:
         case IrInstructionIdIntToEnum:
+        case IrInstructionIdIntToErr:
+        case IrInstructionIdErrToInt:
         case IrInstructionIdTestType:
         case IrInstructionIdTypeName:
         case IrInstructionIdCanImplicitCast:
src/ir_print.cpp
@@ -799,6 +799,16 @@ static void ir_print_int_to_enum(IrPrint *irp, IrInstructionIntToEnum *instructi
     fprintf(irp->f, ")");
 }
 
+static void ir_print_int_to_err(IrPrint *irp, IrInstructionIntToErr *instruction) {
+    fprintf(irp->f, "inttoerr ");
+    ir_print_other_instruction(irp, instruction->target);
+}
+
+static void ir_print_err_to_int(IrPrint *irp, IrInstructionErrToInt *instruction) {
+    fprintf(irp->f, "errtoint ");
+    ir_print_other_instruction(irp, instruction->target);
+}
+
 static void ir_print_check_switch_prongs(IrPrint *irp, IrInstructionCheckSwitchProngs *instruction) {
     fprintf(irp->f, "@checkSwitchProngs(");
     ir_print_other_instruction(irp, instruction->target_value);
@@ -1117,6 +1127,12 @@ static void ir_print_instruction(IrPrint *irp, IrInstruction *instruction) {
         case IrInstructionIdIntToEnum:
             ir_print_int_to_enum(irp, (IrInstructionIntToEnum *)instruction);
             break;
+        case IrInstructionIdIntToErr:
+            ir_print_int_to_err(irp, (IrInstructionIntToErr *)instruction);
+            break;
+        case IrInstructionIdErrToInt:
+            ir_print_err_to_int(irp, (IrInstructionErrToInt *)instruction);
+            break;
         case IrInstructionIdCheckSwitchProngs:
             ir_print_check_switch_prongs(irp, (IrInstructionCheckSwitchProngs *)instruction);
             break;
std/os/darwin.zig
@@ -6,6 +6,10 @@ const arch = switch (@compileVar("arch")) {
 
 const errno = @import("errno.zig");
 
+pub const STDIN_FILENO = 0;
+pub const STDOUT_FILENO = 1;
+pub const STDERR_FILENO = 2;
+
 pub const O_LARGEFILE = 0x0000;
 pub const O_RDONLY = 0x0000;
 
std/os/index.zig
@@ -7,12 +7,26 @@ pub const posix = switch(@compileVar("os")) {
     Os.windows => windows,
     else => @compileError("Unsupported OS"),
 };
+const debug = @import("../debug.zig");
+const assert = debug.assert;
 
 const errno = @import("errno.zig");
 const linking_libc = @import("../target.zig").linking_libc;
 const c = @import("../c/index.zig");
 
+const mem = @import("../mem.zig");
+const Allocator = mem.Allocator;
+
+const io = @import("../io.zig");
+
 error Unexpected;
+error SysResources;
+error AccessDenied;
+error InvalidExe;
+error FileSystem;
+error IsDir;
+error FileNotFound;
+error FileBusy;
 
 /// Fills `buf` with random bytes. If linking against libc, this calls the
 /// appropriate OS-specific library call. Otherwise it uses the zig standard
@@ -76,3 +90,332 @@ pub coldcc fn abort() -> noreturn {
         else => @compileError("Unsupported OS"),
     }
 }
+
+fn makePipe() -> %[2]i32 {
+    var fds: [2]i32 = undefined;
+    const err = posix.getErrno(posix.pipe(&fds));
+    if (err > 0) {
+        return switch (err) {
+            errno.EMFILE, errno.ENFILE => error.SysResources,
+            else => error.Unexpected,
+        }
+    }
+    return fds;
+}
+
+fn destroyPipe(pipe: &const [2]i32) {
+    closeNoIntr((*pipe)[0]);
+    closeNoIntr((*pipe)[1]);
+}
+
+fn closeNoIntr(fd: i32) {
+    while (true) {
+        const err = posix.getErrno(posix.close(fd));
+        if (err == errno.EINTR) {
+            continue;
+        } else {
+            return;
+        }
+    }
+}
+
+fn openNoIntr(path: []const u8, flags: usize, perm: usize) -> %i32 {
+    while (true) {
+        const result = posix.open(path, flags, perm);
+        const err = posix.getErrno(result);
+        if (err > 0) {
+            return switch (err) {
+                errno.EINTR => continue,
+
+                errno.EFAULT => unreachable,
+                errno.EINVAL => unreachable,
+                errno.EACCES => error.BadPerm,
+                errno.EFBIG, errno.EOVERFLOW => error.FileTooBig,
+                errno.EISDIR => error.IsDir,
+                errno.ELOOP => error.SymLinkLoop,
+                errno.EMFILE => error.ProcessFdQuotaExceeded,
+                errno.ENAMETOOLONG => error.NameTooLong,
+                errno.ENFILE => error.SystemFdQuotaExceeded,
+                errno.ENODEV => error.NoDevice,
+                errno.ENOENT => error.PathNotFound,
+                errno.ENOMEM => error.NoMem,
+                errno.ENOSPC => error.NoSpaceLeft,
+                errno.ENOTDIR => error.NotDir,
+                errno.EPERM => error.BadPerm,
+                else => error.Unexpected,
+            }
+        }
+        return i32(result);
+    }
+}
+
+const ErrInt = @intType(false, @sizeOf(error) * 8);
+fn writeIntFd(fd: i32, value: ErrInt) -> %void {
+    var bytes: [@sizeOf(ErrInt)]u8 = undefined;
+    mem.writeInt(bytes[0...], value, true);
+
+    var index: usize = 0;
+    while (index < bytes.len) {
+        const amt_written = posix.write(fd, &bytes[index], bytes.len - index);
+        const err = posix.getErrno(amt_written);
+        if (err > 0) {
+            switch (err) {
+                errno.EINTR => continue,
+                errno.EINVAL => unreachable,
+                else => return error.SysResources,
+            }
+        }
+        index += amt_written;
+    }
+}
+
+fn readIntFd(fd: i32) -> %ErrInt {
+    var bytes: [@sizeOf(ErrInt)]u8 = undefined;
+
+    var index: usize = 0;
+    while (index < bytes.len) {
+        const amt_written = posix.read(fd, &bytes[index], bytes.len - index);
+        const err = posix.getErrno(amt_written);
+        if (err > 0) {
+            switch (err) {
+                errno.EINTR => continue,
+                errno.EINVAL => unreachable,
+                else => return error.SysResources,
+            }
+        }
+        index += amt_written;
+    }
+
+    return mem.readInt(bytes[0...], ErrInt, true);
+}
+
+// Child of fork calls this to report an error to the fork parent.
+// Then the child exits.
+fn forkChildErrReport(fd: i32, err: error) -> noreturn {
+    _ = writeIntFd(fd, ErrInt(err));
+    posix.exit(1);
+}
+
+fn dup2NoIntr(old_fd: i32, new_fd: i32) -> %void {
+    while (true) {
+        const err = posix.getErrno(posix.dup2(old_fd, new_fd));
+        if (err > 0) {
+            return switch (err) {
+                errno.EBUSY, errno.EINTR => continue,
+                errno.EMFILE => error.SysResources,
+                errno.EINVAL => unreachable,
+                else => error.Unexpected,
+            };
+        }
+        return;
+    }
+}
+
+pub const ChildProcess = struct {
+    pid: i32,
+    err_pipe: [2]i32,
+
+    stdin: ?io.OutStream,
+    stdout: ?io.InStream,
+    stderr: ?io.InStream,
+
+    pub const Term = enum {
+        Clean: i32,
+        Signal: i32,
+        Stopped: i32,
+        Unknown: i32,
+    };
+
+    pub const StdIo = enum {
+        Inherit,
+        Ignore,
+        Pipe,
+        Close,
+    };
+
+    pub fn spawn(exe_path: []const u8, args: []const []const u8, env: []const []const u8,
+        stdin: StdIo, stdout: StdIo, stderr: StdIo) -> %ChildProcess
+    {
+        switch (@compileVar("os")) {
+            Os.linux, Os.macosx, Os.ios, Os.darwin => {
+                return spawnPosix(exe_path, args, env, stdin, stdout, stderr);
+            },
+            else => @compileError("Unsupported OS"),
+        }
+    }
+
+    pub fn wait(self: &ChildProcess) -> %Term {
+        defer {
+            closeNoIntr(self.err_pipe[0]);
+            closeNoIntr(self.err_pipe[1]);
+        };
+
+        var status: i32 = undefined;
+        while (true) {
+            const err = posix.getErrno(posix.waitpid(self.pid, &status, 0));
+            if (err > 0) {
+                switch (err) {
+                    errno.EINVAL, errno.ECHILD => unreachable,
+                    errno.EINTR => continue,
+                    else => {
+                        if (const *stdin ?= self.stdin) { stdin.close(); }
+                        if (const *stdout ?= self.stdin) { stdout.close(); }
+                        if (const *stderr ?= self.stdin) { stderr.close(); }
+                        return error.Unexpected;
+                    },
+                }
+            }
+            break;
+        }
+
+        if (const *stdin ?= self.stdin) { stdin.close(); }
+        if (const *stdout ?= self.stdin) { stdout.close(); }
+        if (const *stderr ?= self.stdin) { stderr.close(); }
+
+        // Write @maxValue(ErrInt) to the write end of the err_pipe. This is after
+        // waitpid, so this write is guaranteed to be after the child
+        // pid potentially wrote an error. This way we can do a blocking
+        // read on the error pipe and either get @maxValue(ErrInt) (no error) or
+        // an error code.
+        %return writeIntFd(self.err_pipe[1], @maxValue(ErrInt));
+        const err_int = %return readIntFd(self.err_pipe[0]);
+        // Here we potentially return the fork child's error
+        // from the parent pid.
+        if (err_int != @maxValue(ErrInt)) {
+            return error(err_int);
+        }
+
+        return statusToTerm(status);
+    }
+
+    fn statusToTerm(status: i32) -> Term {
+        return if (posix.WIFEXITED(status)) {
+            Term.Clean { posix.WEXITSTATUS(status) }
+        } else if (posix.WIFSIGNALED(status)) {
+            Term.Signal { posix.WTERMSIG(status) }
+        } else if (posix.WIFSTOPPED(status)) {
+            Term.Stopped { posix.WSTOPSIG(status) }
+        } else {
+            Term.Unknown { status }
+        };
+    }
+
+    fn spawnPosix(exe_path: []const u8, args: []const []const u8, env: []const []const u8,
+        stdin: StdIo, stdout: StdIo, stderr: StdIo) -> %ChildProcess
+    {
+        // TODO issue #295
+        //const stdin_pipe = if (stdin == StdIo.Pipe) %return makePipe() else undefined;
+        var stdin_pipe: [2]i32 = undefined;
+        if (stdin == StdIo.Pipe)
+            stdin_pipe = %return makePipe();
+        %defer if (stdin == StdIo.Pipe) { destroyPipe(stdin_pipe); };
+
+        // TODO issue #295
+        //const stdout_pipe = if (stdout == StdIo.Pipe) %return makePipe() else undefined;
+        var stdout_pipe: [2]i32 = undefined;
+        if (stdout == StdIo.Pipe) 
+            stdout_pipe = %return makePipe();
+        %defer if (stdout == StdIo.Pipe) { destroyPipe(stdout_pipe); };
+
+        // TODO issue #295
+        //const stderr_pipe = if (stderr == StdIo.Pipe) %return makePipe() else undefined;
+        var stderr_pipe: [2]i32 = undefined;
+        if (stderr == StdIo.Pipe) 
+            stderr_pipe = %return makePipe();
+        %defer if (stderr == StdIo.Pipe) { destroyPipe(stderr_pipe); };
+
+        const any_ignore = (stdin == StdIo.Ignore or stdout == StdIo.Ignore or stderr == StdIo.Ignore);
+        // TODO issue #295
+        //const dev_null_fd = if (any_ignore) {
+        //    %return openNoIntr("/dev/null", posix.O_RDWR, 0)
+        //} else {
+        //    undefined
+        //};
+        var dev_null_fd: i32 = undefined;
+        if (any_ignore)
+            dev_null_fd = %return openNoIntr("/dev/null", posix.O_RDWR, 0);
+
+        // This pipe is used to communicate errors between the time of fork
+        // and execve from the child process to the parent process.
+        const err_pipe = %return makePipe();
+        %defer destroyPipe(err_pipe);
+
+        const pid = posix.fork();
+        const pid_err = linux.getErrno(pid);
+        if (pid_err > 0) {
+            return switch (pid_err) {
+                errno.EAGAIN, errno.ENOMEM, errno.ENOSYS => error.SysResources,
+                else => error.Unexpected,
+            };
+        }
+        if (pid == 0) {
+            // we are the child
+            setUpChildIo(stdin, stdin_pipe[0], posix.STDIN_FILENO, dev_null_fd) %%
+                |err| forkChildErrReport(err_pipe[1], err);
+            setUpChildIo(stdout, stdout_pipe[1], posix.STDOUT_FILENO, dev_null_fd) %%
+                |err| forkChildErrReport(err_pipe[1], err);
+            setUpChildIo(stderr, stderr_pipe[1], posix.STDERR_FILENO, dev_null_fd) %%
+                |err| forkChildErrReport(err_pipe[1], err);
+
+            const err = posix.getErrno(posix.execve(exe_path, args, env));
+            assert(err > 0);
+            forkChildErrReport(err_pipe[1], switch (err) {
+                errno.EFAULT => unreachable,
+                errno.E2BIG, errno.EMFILE, errno.ENAMETOOLONG, errno.ENFILE, errno.ENOMEM => error.SysResources,
+                errno.EACCES, errno.EPERM => error.AccessDenied,
+                errno.EINVAL, errno.ENOEXEC => error.InvalidExe,
+                errno.EIO, errno.ELOOP => error.FileSystem,
+                errno.EISDIR => error.IsDir,
+                errno.ENOENT, errno.ENOTDIR => error.FileNotFound,
+                errno.ETXTBSY => error.FileBusy,
+                else => error.Unexpected,
+            });
+        }
+
+        // we are the parent
+        if (stdin == StdIo.Pipe) { closeNoIntr(stdin_pipe[0]); }
+        if (stdout == StdIo.Pipe) { closeNoIntr(stdout_pipe[1]); }
+        if (stderr == StdIo.Pipe) { closeNoIntr(stderr_pipe[1]); }
+        if (any_ignore) { closeNoIntr(dev_null_fd); }
+
+        return ChildProcess {
+            .pid = i32(pid),
+            .err_pipe = err_pipe,
+
+            .stdin = if (stdin == StdIo.Pipe) {
+                io.OutStream {
+                    .fd = stdin_pipe[1],
+                }
+            } else {
+                null
+            },
+            .stdout = if (stdout == StdIo.Pipe) {
+                io.InStream {
+                    .fd = stdout_pipe[0],
+                    .buffer = undefined,
+                    .index = 0,
+                }
+            } else {
+                null
+            },
+            .stderr = if (stderr == StdIo.Pipe) {
+                io.InStream {
+                    .fd = stderr_pipe[0],
+                    .buffer = undefined,
+                    .index = 0,
+                }
+            } else {
+                null
+            },
+        };
+    }
+
+    fn setUpChildIo(stdio: StdIo, pipe_fd: i32, std_fileno: i32, dev_null_fd: i32) -> %void {
+        switch (stdio) {
+            StdIo.Pipe => %return dup2NoIntr(pipe_fd, std_fileno),
+            StdIo.Close => closeNoIntr(std_fileno),
+            StdIo.Inherit => {},
+            StdIo.Ignore => %return dup2NoIntr(dev_null_fd, std_fileno),
+        }
+    }
+};
std/os/linux.zig
@@ -5,6 +5,10 @@ const arch = switch (@compileVar("arch")) {
 };
 const errno = @import("errno.zig");
 
+pub const STDIN_FILENO = 0;
+pub const STDOUT_FILENO = 1;
+pub const STDERR_FILENO = 2;
+
 pub const PROT_NONE      = 0;
 pub const PROT_READ      = 1;
 pub const PROT_WRITE     = 2;
@@ -237,12 +241,66 @@ pub const AF_NFC = PF_NFC;
 pub const AF_VSOCK = PF_VSOCK;
 pub const AF_MAX = PF_MAX;
 
+
+fn unsigned(s: i32) -> u32 { *@ptrcast(&u32, &s) }
+fn signed(s: u32) -> i32 { *@ptrcast(&i32, &s) }
+pub fn WEXITSTATUS(s: i32) -> i32 { signed((unsigned(s) & 0xff00) >> 8) }
+pub fn WTERMSIG(s: i32) -> i32 { signed(unsigned(s) & 0x7f) }
+pub fn WSTOPSIG(s: i32) -> i32 { WEXITSTATUS(s) }
+pub fn WIFEXITED(s: i32) -> bool { WTERMSIG(s) == 0 }
+pub fn WIFSTOPPED(s: i32) -> bool { (u16)(((unsigned(s)&0xffff)*%0x10001)>>8) > 0x7f00 }
+pub fn WIFSIGNALED(s: i32) -> bool { (unsigned(s)&0xffff)-%1 < 0xff }
+
 /// Get the errno from a syscall return value, or 0 for no error.
 pub fn getErrno(r: usize) -> usize {
     const signed_r = *@ptrcast(&isize, &r);
     if (signed_r > -4096 and signed_r < 0) usize(-signed_r) else 0
 }
 
+pub fn dup2(old: i32, new: i32) -> usize {
+    arch.syscall2(arch.SYS_dup2, usize(old), usize(new))
+}
+
+pub fn execve_c(path: &const u8, argv: &const ?&const u8, envp: &const ?&const u8) -> usize {
+    arch.syscall3(arch.SYS_execve, path, argv, envp)
+}
+
+/// This function must allocate memory to add a null terminating bytes on path, each arg,
+/// and each environment variable line, as well as a null pointer after the arg list and
+/// environment variable list. We allocate stack memory since the process is about to get
+/// wiped anyway.
+pub fn execve(path: []const u8, argv: []const []const u8, envp: []const []const u8) -> usize {
+    const path_buf = @alloca(u8, path.len + 1);
+    @memcpy(&path_buf[0], &path[0], path.len);
+    path_buf[path.len] = 0;
+
+    const argv_buf = @alloca([]const ?&const u8, argv.len + 1);
+    for (argv) |arg, i| {
+        const arg_buf = @alloca(u8, arg.len + 1);
+        @memcpy(&arg_buf[0], &arg[0], arg.len);
+        arg_buf[arg.len] = 0;
+
+        argv[i] = arg_buf;
+    }
+    argv_buf[argv.len] = null;
+
+    const envp_buf = @alloca([]const ?&const u8, envp.len + 1);
+    for (envp) |env, i| {
+        const env_buf = @alloca(u8, env.len + 1);
+        @memcpy(&env_buf[0], &env[0], env.len);
+        env_buf[env.len] = 0;
+
+        envp[i] = env_buf;
+    }
+    envp_buf[envp.len] = null;
+
+    return execve_c(path_buf.ptr, argv_buf.ptr, envp_buf.ptr);
+}
+
+pub fn fork() -> usize {
+    arch.syscall0(arch.SYS_fork)
+}
+
 pub fn mmap(address: ?&u8, length: usize, prot: usize, flags: usize, fd: i32, offset: usize)
     -> usize
 {
@@ -261,6 +319,14 @@ pub fn pread(fd: i32, buf: &u8, count: usize, offset: usize) -> usize {
     arch.syscall4(arch.SYS_pread, usize(fd), usize(buf), count, offset)
 }
 
+pub fn pipe(fd: &[2]i32) -> usize {
+    pipe2(fd, 0)
+}
+
+pub fn pipe2(fd: &[2]i32, flags: usize) -> usize {
+    arch.syscall2(arch.SYS_pipe2, usize(fd), flags)
+}
+
 pub fn write(fd: i32, buf: &const u8, count: usize) -> usize {
     arch.syscall3(arch.SYS_write, usize(fd), usize(buf), count)
 }
@@ -319,8 +385,12 @@ pub fn getrandom(buf: &u8, count: usize, flags: u32) -> usize {
     arch.syscall3(arch.SYS_getrandom, usize(buf), count, usize(flags))
 }
 
-pub fn kill(pid: i32, sig: i32) -> i32 {
-    i32(arch.syscall2(arch.SYS_kill, usize(pid), usize(sig)))
+pub fn kill(pid: i32, sig: i32) -> usize {
+    arch.syscall2(arch.SYS_kill, usize(pid), usize(sig))
+}
+
+pub fn waitpid(pid: i32, status: &i32, options: i32) -> usize {
+    arch.syscall4(arch.SYS_wait4, usize(pid), usize(status), usize(options), 0)
 }
 
 const NSIG = 65;
std/build.zig
@@ -3,8 +3,12 @@ const mem = @import("mem.zig");
 const debug = @import("debug.zig");
 const List = @import("list.zig").List;
 const Allocator = @import("mem.zig").Allocator;
+const os = @import("os/index.zig");
+const StdIo = os.ChildProcess.StdIo;
+const Term = os.ChildProcess.Term;
 
 error ExtraArg;
+error UncleanExit;
 
 pub const Builder = struct {
     zig_exe: []const u8,
@@ -33,9 +37,9 @@ pub const Builder = struct {
         return exe;
     }
 
-    pub fn make(self: &Builder, args: []const []const u8) -> %void {
+    pub fn make(self: &Builder, cli_args: []const []const u8) -> %void {
         var verbose = false;
-        for (args) |arg| {
+        for (cli_args) |arg| {
             if (mem.eql(u8, arg, "--verbose")) {
                 verbose = true;
             } else {
@@ -44,7 +48,27 @@ pub const Builder = struct {
             }
         }
         for (self.exe_list.toSlice()) |exe| {
-            %%io.stderr.printf("TODO: invoke this command:\nzig build_exe {} --name {}\n", exe.root_src, exe.name);
+            var zig_args = List([]const u8).init(self.allocator);
+            defer zig_args.deinit();
+
+            %return zig_args.append("build_exe"[0...]); // TODO issue #296
+            %return zig_args.append(exe.root_src);
+            %return zig_args.append("--name"[0...]); // TODO issue #296
+            %return zig_args.append(exe.name);
+
+            printInvocation(self.zig_exe, zig_args);
+            const TODO_env: []const []const u8 = undefined; // TODO
+            var child = %return os.ChildProcess.spawn(self.zig_exe, zig_args.toSliceConst(), TODO_env,
+                StdIo.Ignore, StdIo.Inherit, StdIo.Inherit);
+            const term = %return child.wait();
+            switch (term) {
+                Term.Clean => |code| {
+                    if (code != 0) {
+                        return error.UncleanExit;
+                    }
+                },
+                else => return error.UncleanExit,
+            }
         }
     }
 };
@@ -57,3 +81,11 @@ const Exe = struct {
 fn handleErr(err: error) -> noreturn {
     debug.panic("error: {}\n", @errorName(err));
 }
+
+fn printInvocation(exe_name: []const u8, args: &const List([]const u8)) {
+    %%io.stderr.printf("{}", exe_name);
+    for (args.toSliceConst()) |arg| {
+        %%io.stderr.printf(" {}", arg);
+    }
+    %%io.stderr.printf("\n");
+}
std/io.zig
@@ -13,22 +13,18 @@ const mem = @import("mem.zig");
 const Buffer0 = @import("cstr.zig").Buffer0;
 const fmt = @import("fmt.zig");
 
-pub const stdin_fileno = 0;
-pub const stdout_fileno = 1;
-pub const stderr_fileno = 2;
-
 pub var stdin = InStream {
-    .fd = stdin_fileno,
+    .fd = system.STDIN_FILENO,
 };
 
 pub var stdout = OutStream {
-    .fd = stdout_fileno,
+    .fd = system.STDOUT_FILENO,
     .buffer = undefined,
     .index = 0,
 };
 
 pub var stderr = OutStream {
-    .fd = stderr_fileno,
+    .fd = system.STDERR_FILENO,
     .buffer = undefined,
     .index = 0,
 };
@@ -234,7 +230,6 @@ pub const InStream = struct {
                     if (read_err > 0) {
                         switch (read_err) {
                             errno.EINTR  => continue,
-
                             errno.EINVAL => unreachable,
                             errno.EFAULT => unreachable,
                             errno.EBADF  => return error.BadFd,
@@ -247,7 +242,7 @@ pub const InStream = struct {
                 }
                 return index;
             },
-            else => @compileError("unsupported OS"),
+            else => @compileError("Unsupported OS"),
         }
     }
 
test/cases/cast.zig
@@ -30,3 +30,14 @@ test "implicitly cast a pointer to a const pointer of it" {
 fn funcWithConstPtrPtr(x: &const &i32) {
     **x += 1;
 }
+
+error ItBroke;
+test "explicit cast from integer to error type" {
+    testCastIntToErr(error.ItBroke);
+    comptime testCastIntToErr(error.ItBroke);
+}
+fn testCastIntToErr(err: error) {
+    const x = usize(err);
+    const y = error(x);
+    assert(error.ItBroke == y);
+}
test/run_tests.cpp
@@ -1758,6 +1758,13 @@ export fn foo() {
 }
     )SOURCE", 1, ".tmp_source.zig:3:5: error: unable to infer variable type");
 
+    add_compile_fail_case("undefined literal on a non-comptime var", R"SOURCE(
+export fn foo() {
+    var i = undefined;
+    i = i32(1);
+}
+    )SOURCE", 1, ".tmp_source.zig:3:5: error: unable to infer variable type");
+
     add_compile_fail_case("dereference an array", R"SOURCE(
 var s_buffer: [10]u8 = undefined;
 pub fn pass(in: []u8) -> []u8 {
@@ -1818,6 +1825,15 @@ export fn entry(a: &i32) -> usize {
     return @ptrcast(usize, a);
 }
     )SOURCE", 1, ".tmp_source.zig:3:21: error: expected pointer, found 'usize'");
+
+    add_compile_fail_case("too many error values to cast to small integer", R"SOURCE(
+error A; error B; error C; error D; error E; error F; error G; error H;
+const u2 = @intType(false, 2);
+fn foo(e: error) -> u2 {
+    return u2(e);
+}
+export fn entry() -> usize { @sizeOf(@typeOf(foo)) }
+    )SOURCE", 1, ".tmp_source.zig:5:14: error: too many error values to fit in 'u2'");
 }
 
 //////////////////////////////////////////////////////////////////////////////
@@ -2043,6 +2059,18 @@ fn bar() -> %void {
 }
     )SOURCE");
 
+    add_debug_safety_case("cast integer to error and no code matches", R"SOURCE(
+pub fn panic(message: []const u8) -> noreturn {
+    @breakpoint();
+    while (true) {}
+}
+pub fn main(args: [][]u8) -> %void {
+    _ = bar(9999);
+}
+fn bar(x: u32) -> error {
+    return error(x);
+}
+    )SOURCE");
 }
 
 //////////////////////////////////////////////////////////////////////////////