From 55e852080d459b9b2be18cf41de60c3338f266af Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Tue, 29 Sep 2015 08:40:09 +0200 Subject: epp: Add the pre-defined macro OTP_RELEASE Add a new pre-defined macro called OTP_RELEASE that will expand to an integer being the OTP version. Thus, in OTP 19 the value will be the integer 19. The OTP_RELEASE macro is particularly useful in order to have different source code depending on new language features or new features in the type specification syntax. Those features are only introduced in major versions of OTP. To be truly useful, the -if preprocessor directive need to be implemented. That is the purpose of the next commit. Code that will need to work in both OTP 18 and OTP 19 can be structured in the following way: -ifdef(OTP_RELEASE). %% Code that only works in OTP 19 and later. -else. %% Code that will work in OTP 18. -endif. --- lib/stdlib/src/epp.erl | 4 +++- lib/stdlib/test/epp_SUITE.erl | 3 ++- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/lib/stdlib/src/epp.erl b/lib/stdlib/src/epp.erl index 77cc88eb08..e823156af1 100644 --- a/lib/stdlib/src/epp.erl +++ b/lib/stdlib/src/epp.erl @@ -571,6 +571,7 @@ init_server(Pid, Name, Options, St0) -> predef_macros(File) -> Machine = list_to_atom(erlang:system_info(machine)), Anno = line1(), + OtpVersion = list_to_integer(erlang:system_info(otp_release)), Defs = [{'FILE', {none,[{string,Anno,File}]}}, {'FUNCTION_NAME', undefined}, {'FUNCTION_ARITY', undefined}, @@ -580,7 +581,8 @@ predef_macros(File) -> {'BASE_MODULE', undefined}, {'BASE_MODULE_STRING', undefined}, {'MACHINE', {none,[{atom,Anno,Machine}]}}, - {Machine, {none,[{atom,Anno,true}]}} + {Machine, {none,[{atom,Anno,true}]}}, + {'OTP_RELEASE', {none,[{integer,Anno,OtpVersion}]}} ], maps:from_list(Defs). diff --git a/lib/stdlib/test/epp_SUITE.erl b/lib/stdlib/test/epp_SUITE.erl index 9123bf2f28..87e906a3d4 100644 --- a/lib/stdlib/test/epp_SUITE.erl +++ b/lib/stdlib/test/epp_SUITE.erl @@ -799,7 +799,8 @@ otp_8130(Config) when is_list(Config) -> PreDefMacs = macs(Epp), ['BASE_MODULE','BASE_MODULE_STRING','BEAM','FILE', 'FUNCTION_ARITY','FUNCTION_NAME', - 'LINE','MACHINE','MODULE','MODULE_STRING'] = PreDefMacs, + 'LINE','MACHINE','MODULE','MODULE_STRING', + 'OTP_RELEASE'] = PreDefMacs, {ok,[{'-',_},{atom,_,file}|_]} = epp:scan_erl_form(Epp), {ok,[{'-',_},{atom,_,module}|_]} = epp:scan_erl_form(Epp), {ok,[{atom,_,t}|_]} = epp:scan_erl_form(Epp), -- cgit v1.2.3 From 109b1dc2e346efc37f8c5cfecbf0fa2a476b14fa Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Tue, 29 Sep 2015 09:24:32 +0200 Subject: epp: Implement the -if and -elif preprocessor directives Libraries or applications that support more than one major release of OTP may need to use conditional compilation of Erlang source code. Here are few examples where it would be necessary or desirable: * To support a new data type or language feature only available in the latest major release (real-world examples: maps and the stacktrace syntax). * To avoid warnings for deprecated functions. * To avoid dialyzer warnings. Previously, to do conditional compilation, one would have to use a parse transform or some external tool such as 'autoconf'. To simplify conditional compilation, introduce the -if and -elif preprocessor directives, to allow code like this to be written: -if(?OTP_RELEASE =:= 21). %% Code that will only work in OTP 21. -else. %% Fallback code. -endif. What kind of expressions should be allowed after an -if? We certainly don't want to allow anything with a side effect, such as a '!' or a 'receive'. We also don't want it to be possible to call erlang:system_info/1, as that could make the code depedent on features of the run-time system that could change very easily (such as the number of schedulers). Requiring the expression to be a guard expression makes most sense. It is to explain in the documentation and easy for users to understand. For simplicity of implementation, only a single guard expression will be supported; that is, the ',' and ';' syntax for guards is not supported. To allow some useful conditions to be written, there is a special built-in function: defined(Symbol) tests whether the preprocessor symbol is defined, just like -ifdef. The reason for having this defined/1 is that the defined test can be combined with other tests, for example: 'defined(SOME_NAME) andalso ?OTP_RELEASE > 21'. --- lib/stdlib/src/epp.erl | 123 +++++++++++++++++++++++++++++-- lib/stdlib/test/epp_SUITE.erl | 168 ++++++++++++++++++++++++++++++++++++------ 2 files changed, 262 insertions(+), 29 deletions(-) diff --git a/lib/stdlib/src/epp.erl b/lib/stdlib/src/epp.erl index e823156af1..cc34d4bdd3 100644 --- a/lib/stdlib/src/epp.erl +++ b/lib/stdlib/src/epp.erl @@ -38,7 +38,7 @@ -type epp_handle() :: pid(). -type source_encoding() :: latin1 | utf8. --type ifdef() :: 'ifdef' | 'ifndef' | 'else'. +-type ifdef() :: 'ifdef' | 'ifndef' | 'if' | 'else'. -type name() :: atom(). -type argspec() :: 'none' %No arguments @@ -221,6 +221,8 @@ format_error({illegal_function,Macro}) -> io_lib:format("?~s can only be used within a function", [Macro]); format_error({illegal_function_usage,Macro}) -> io_lib:format("?~s must not begin a form", [Macro]); +format_error(elif_after_else) -> + "'elif' following 'else'"; format_error({'NYI',What}) -> io_lib:format("not yet implemented '~s'", [What]); format_error({error,Term}) -> @@ -1087,21 +1089,118 @@ scan_else(_Toks, Else, From, St) -> epp_reply(From, {error,{loc(Else),epp,{bad,'else'}}}), wait_req_scan(St). -%% scan_if(Tokens, EndifToken, From, EppState) +%% scan_if(Tokens, IfToken, From, EppState) %% Handle the conditional parsing of a file. -%% Report a badly formed if test and then treat as false macro. +scan_if([{'(',_}|_]=Toks, If, From, St) -> + try eval_if(Toks, St) of + true -> + scan_toks(From, St#epp{istk=['if'|St#epp.istk]}); + _ -> + skip_toks(From, St, ['if']) + catch + throw:Error0 -> + Error = case Error0 of + {_,erl_parse,_} -> + {error,Error0}; + _ -> + {error,{loc(If),epp,Error0}} + end, + epp_reply(From, Error), + wait_req_skip(St, ['if']) + end; scan_if(_Toks, If, From, St) -> - epp_reply(From, {error,{loc(If),epp,{'NYI','if'}}}), + epp_reply(From, {error,{loc(If),epp,{bad,'if'}}}), wait_req_skip(St, ['if']). +eval_if(Toks0, St) -> + Toks = expand_macros(Toks0, St), + Es1 = case erl_parse:parse_exprs(Toks) of + {ok,Es0} -> Es0; + {error,E} -> throw(E) + end, + Es = rewrite_expr(Es1, St), + assert_guard_expr(Es), + Bs = erl_eval:new_bindings(), + LocalFun = fun(_Name, _Args) -> + error(badarg) + end, + try erl_eval:exprs(Es, Bs, {value,LocalFun}) of + {value,Res,_} -> + Res + catch + _:_ -> + false + end. + +assert_guard_expr([E0]) -> + E = rewrite_expr(E0, none), + case erl_lint:is_guard_expr(E) of + false -> + throw({bad,'if'}); + true -> + ok + end; +assert_guard_expr(_) -> + throw({bad,'if'}). + +%% Dual-purpose rewriting function. When the second argument is +%% an #epp{} record, calls to defined(Symbol) will be evaluated. +%% When the second argument is 'none', legal calls to our built-in +%% functions are eliminated in order to turn the expression into +%% a legal guard expression. + +rewrite_expr({call,_,{atom,_,defined},[N0]}, #epp{macs=Macs}) -> + %% Evaluate defined(Symbol). + N = case N0 of + {var,_,N1} -> N1; + {atom,_,N1} -> N1; + _ -> throw({bad,'if'}) + end, + {atom,0,maps:is_key(N, Macs)}; +rewrite_expr({call,_,{atom,_,Name},As0}, none) -> + As = rewrite_expr(As0, none), + Arity = length(As), + case erl_internal:bif(Name, Arity) andalso + not erl_internal:guard_bif(Name, Arity) of + false -> + %% A guard BIF, an -if built-in, or an unknown function. + %% Eliminate the call so that erl_lint will not complain. + %% The call might fail later at evaluation time. + to_conses(As); + true -> + %% An auto-imported BIF (not guard BIF). Not allowed. + throw({bad,'if'}) + end; +rewrite_expr([H|T], St) -> + [rewrite_expr(H, St)|rewrite_expr(T, St)]; +rewrite_expr(Tuple, St) when is_tuple(Tuple) -> + list_to_tuple(rewrite_expr(tuple_to_list(Tuple), St)); +rewrite_expr(Other, _) -> + Other. + +to_conses([H|T]) -> + {cons,0,H,to_conses(T)}; +to_conses([]) -> + {nil,0}. + %% scan_elif(Tokens, EndifToken, From, EppState) %% Handle the conditional parsing of a file. %% Report a badly formed if test and then treat as false macro. scan_elif(_Toks, Elif, From, St) -> - epp_reply(From, {error,{loc(Elif),epp,{'NYI','elif'}}}), - wait_req_scan(St). + case St#epp.istk of + ['else'|Cis] -> + epp_reply(From, {error,{loc(Elif), + epp,{illegal,"unbalanced",'elif'}}}), + wait_req_skip(St#epp{istk=Cis}, ['else']); + [_I|Cis] -> + skip_toks(From, St#epp{istk=Cis}, ['elif']); + [] -> + epp_reply(From, {error,{loc(Elif),epp, + {illegal,"unbalanced",elif}}}), + wait_req_scan(St) + end. %% scan_endif(Tokens, EndifToken, From, EppState) %% If we are in an if body then exit it, else report an error. @@ -1160,6 +1259,8 @@ skip_toks(From, St, [I|Sis]) -> skip_toks(From, St#epp{location=Cl}, ['if',I|Sis]); {ok,[{'-',_Lh},{atom,_Le,'else'}=Else|_Toks],Cl}-> skip_else(Else, From, St#epp{location=Cl}, [I|Sis]); + {ok,[{'-',_Lh},{atom,_Le,'elif'}=Elif|Toks],Cl}-> + skip_elif(Toks, Elif, From, St#epp{location=Cl}, [I|Sis]); {ok,[{'-',_Lh},{atom,_Le,endif}|_Toks],Cl} -> skip_toks(From, St#epp{location=Cl}, Sis); {ok,_Toks,Cl} -> @@ -1190,11 +1291,21 @@ skip_toks(From, St, []) -> skip_else(Else, From, St, ['else'|Sis]) -> epp_reply(From, {error,{loc(Else),epp,{illegal,"repeated",'else'}}}), wait_req_skip(St, ['else'|Sis]); +skip_else(_Else, From, St, ['elif'|Sis]) -> + skip_toks(From, St, ['else'|Sis]); skip_else(_Else, From, St, [_I]) -> scan_toks(From, St#epp{istk=['else'|St#epp.istk]}); skip_else(_Else, From, St, Sis) -> skip_toks(From, St, Sis). +skip_elif(_Toks, Elif, From, St, ['else'|_]=Sis) -> + epp_reply(From, {error,{loc(Elif),epp,elif_after_else}}), + wait_req_skip(St, Sis); +skip_elif(Toks, Elif, From, St, [_I]) -> + scan_if(Toks, Elif, From, St); +skip_elif(_Toks, _Elif, From, St, Sis) -> + skip_toks(From, St, Sis). + %% macro_pars(Tokens, ArgStack) %% macro_expansion(Tokens, Anno) %% Extract the macro parameters and the expansion from a macro definition. diff --git a/lib/stdlib/test/epp_SUITE.erl b/lib/stdlib/test/epp_SUITE.erl index 87e906a3d4..a3e294ffea 100644 --- a/lib/stdlib/test/epp_SUITE.erl +++ b/lib/stdlib/test/epp_SUITE.erl @@ -28,7 +28,8 @@ otp_8130/1, overload_mac/1, otp_8388/1, otp_8470/1, otp_8562/1, otp_8665/1, otp_8911/1, otp_10302/1, otp_10820/1, otp_11728/1, encoding/1, extends/1, function_macro/1, - test_error/1, test_warning/1, otp_14285/1]). + test_error/1, test_warning/1, otp_14285/1, + test_if/1]). -export([epp_parse_erl_form/2]). @@ -69,7 +70,7 @@ all() -> overload_mac, otp_8388, otp_8470, otp_8562, otp_8665, otp_8911, otp_10302, otp_10820, otp_11728, encoding, extends, function_macro, test_error, test_warning, - otp_14285]. + otp_14285, test_if]. groups() -> [{upcase_mac, [], [upcase_mac_1, upcase_mac_2]}, @@ -953,27 +954,7 @@ ifdef(Config) -> {define_c5, <<"-\ndefine a.\n">>, - {errors,[{{2,1},epp,{bad,define}}],[]}}, - - {define_c6, - <<"\n-if.\n" - "-endif.\n">>, - {errors,[{{2,2},epp,{'NYI','if'}}],[]}}, - - {define_c7, - <<"-ifndef(a).\n" - "-elif.\n" - "-endif.\n">>, - {errors,[{{2,2},epp,{'NYI',elif}}],[]}}, - - {define_c7, - <<"-ifndef(a).\n" - "-if.\n" - "-elif.\n" - "-endif.\n" - "-endif.\n" - "t() -> a.\n">>, - {errors,[{{2,2},epp,{'NYI','if'}}],[]}} + {errors,[{{2,1},epp,{bad,define}}],[]}} ], [] = compile(Config, Cs), @@ -1118,6 +1099,147 @@ test_warning(Config) -> [] = compile(Config, Cs), ok. +%% OTP-12847: Test the -if and -elif directives and the built-in +%% function defined(Symbol). +test_if(Config) -> + Cs = [{if_1c, + <<"-if.\n" + "-endif.\n" + "-if no_parentheses.\n" + "-endif.\n" + "-if(syntax error.\n" + "-endif.\n" + "-if(true).\n" + "-if(a+3).\n" + "syntax error not triggered here.\n" + "-endif.\n">>, + {errors,[{1,epp,{bad,'if'}}, + {3,epp,{bad,'if'}}, + {5,erl_parse,["syntax error before: ","error"]}, + {11,epp,{illegal,"unterminated",'if'}}], + []}}, + + {if_2c, %Bad guard expressions. + <<"-if(is_list(integer_to_list(42))).\n" %Not guard BIF. + "-endif.\n" + "-if(begin true end).\n" + "-endif.\n">>, + {errors,[{1,epp,{bad,'if'}}, + {3,epp,{bad,'if'}}], + []}}, + + {if_3c, %Invalid use of defined/1. + <<"-if defined(42).\n" + "-endif.\n">>, + {errors,[{1,epp,{bad,'if'}}],[]}}, + + {if_4c, + <<"-elif OTP_RELEASE > 18.\n">>, + {errors,[{1,epp,{illegal,"unbalanced",'elif'}}],[]}}, + + {if_5c, + <<"-ifdef(not_defined_today).\n" + "-else.\n" + "-elif OTP_RELEASE > 18.\n" + "-endif.\n">>, + {errors,[{3,epp,{illegal,"unbalanced",'elif'}}],[]}}, + + {if_6c, + <<"-if(defined(OTP_RELEASE)).\n" + "-else.\n" + "-elif(true).\n" + "-endif.\n">>, + {errors,[{3,epp,elif_after_else}],[]}}, + + {if_7c, + <<"-if(begin true end).\n" %Not a guard expression. + "-endif.\n">>, + {errors,[{1,epp,{bad,'if'}}],[]}} + + ], + [] = compile(Config, Cs), + + Ts = [{if_1, + <<"-if(?OTP_RELEASE > 18).\n" + "t() -> ok.\n" + "-else.\n" + "a bug.\n" + "-endif.\n">>, + ok}, + + {if_2, + <<"-if(false).\n" + "a bug.\n" + "-elif(?OTP_RELEASE > 18).\n" + "t() -> ok.\n" + "-else.\n" + "a bug.\n" + "-endif.\n">>, + ok}, + + {if_3, + <<"-if(true).\n" + "t() -> ok.\n" + "-elif(?OTP_RELEASE > 18).\n" + "a bug.\n" + "-else.\n" + "a bug.\n" + "-endif.\n">>, + ok}, + + {if_4, + <<"-define(a, 1).\n" + "-if(defined(a) andalso defined(OTP_RELEASE)).\n" + "t() -> ok.\n" + "-else.\n" + "a bug.\n" + "-endif.\n">>, + ok}, + + {if_5, + <<"-if(defined(a)).\n" + "a bug.\n" + "-else.\n" + "t() -> ok.\n" + "-endif.\n">>, + ok}, + + {if_6, + <<"-if(defined(not_defined_today)).\n" + " -if(true).\n" + " bug1.\n" + " -elif(true).\n" + " bug2.\n" + " -elif(true).\n" + " bug3.\n" + " -else.\n" + " bug4.\n" + " -endif.\n" + "-else.\n" + "t() -> ok.\n" + "-endif.\n">>, + ok}, + + {if_7, + <<"-if(not_builtin()).\n" + "a bug.\n" + "-else.\n" + "t() -> ok.\n" + "-endif.\n">>, + ok}, + + {if_8, + <<"-if(42).\n" %Not boolean. + "a bug.\n" + "-else.\n" + "t() -> ok.\n" + "-endif.\n">>, + ok} + ], + [] = run(Config, Ts), + + ok. + %% Advanced test on overloading macros. overload_mac(Config) when is_list(Config) -> Cs = [ -- cgit v1.2.3 From 71bb5d9272bfa046c3cfe8a419bf70877f141146 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= Date: Mon, 19 Oct 2015 14:04:13 +0200 Subject: syntax_tools: Add support for -if and -elif --- lib/syntax_tools/src/epp_dodger.erl | 36 +++++++++++++++++++++++++++++++-- lib/syntax_tools/src/erl_prettypr.erl | 7 ++++++- lib/syntax_tools/src/erl_syntax_lib.erl | 2 ++ 3 files changed, 42 insertions(+), 3 deletions(-) diff --git a/lib/syntax_tools/src/epp_dodger.erl b/lib/syntax_tools/src/epp_dodger.erl index 0a12e8fd8b..7e741cc649 100644 --- a/lib/syntax_tools/src/epp_dodger.erl +++ b/lib/syntax_tools/src/epp_dodger.erl @@ -502,6 +502,10 @@ quickscan_form([{'-', _L}, {atom, La, ifdef} | _Ts]) -> kill_form(La); quickscan_form([{'-', _L}, {atom, La, ifndef} | _Ts]) -> kill_form(La); +quickscan_form([{'-', _L}, {'if', La} | _Ts]) -> + kill_form(La); +quickscan_form([{'-', _L}, {atom, La, elif} | _Ts]) -> + kill_form(La); quickscan_form([{'-', _L}, {atom, La, else} | _Ts]) -> kill_form(La); quickscan_form([{'-', _L}, {atom, La, endif} | _Ts]) -> @@ -615,8 +619,13 @@ filter_form(T) -> %% --------------------------------------------------------------------- %% Normal parsing - try to preserve all information -normal_parser(Ts, Opt) -> - rewrite_form(parse_tokens(scan_form(Ts, Opt))). +normal_parser(Ts0, Opt) -> + case scan_form(Ts0, Opt) of + Ts when is_list(Ts) -> + rewrite_form(parse_tokens(Ts)); + Node -> + Node + end. scan_form([{'-', _L}, {atom, La, define} | Ts], Opt) -> [{atom, La, ?pp_form}, {'(', La}, {')', La}, {'->', La}, @@ -636,12 +645,26 @@ scan_form([{'-', _L}, {atom, La, ifdef} | Ts], Opt) -> scan_form([{'-', _L}, {atom, La, ifndef} | Ts], Opt) -> [{atom, La, ?pp_form}, {'(', La}, {')', La}, {'->', La}, {atom, La, ifndef} | scan_macros(Ts, Opt)]; +scan_form([{'-', _L}, {'if', La} | Ts], Opt) -> + [{atom, La, ?pp_form}, {'(', La}, {')', La}, {'->', La}, + {atom, La, 'if'} | scan_macros(Ts, Opt)]; +scan_form([{'-', _L}, {atom, La, elif} | Ts], Opt) -> + [{atom, La, ?pp_form}, {'(', La}, {')', La}, {'->', La}, + {atom, La, 'elif'} | scan_macros(Ts, Opt)]; scan_form([{'-', _L}, {atom, La, else} | Ts], Opt) -> [{atom, La, ?pp_form}, {'(', La}, {')', La}, {'->', La}, {atom, La, else} | scan_macros(Ts, Opt)]; scan_form([{'-', _L}, {atom, La, endif} | Ts], Opt) -> [{atom, La, ?pp_form}, {'(', La}, {')', La}, {'->', La}, {atom, La, endif} | scan_macros(Ts, Opt)]; +scan_form([{'-', _L}, {atom, La, error} | Ts], _Opt) -> + Desc = build_info_string("-error", Ts), + ErrorInfo = {La, ?MODULE, {error, Desc}}, + erl_syntax:error_marker(ErrorInfo); +scan_form([{'-', _L}, {atom, La, warning} | Ts], _Opt) -> + Desc = build_info_string("-warning", Ts), + ErrorInfo = {La, ?MODULE, {warning, Desc}}, + erl_syntax:error_marker(ErrorInfo); scan_form([{'-', L}, {'?', L1}, {Type, _, _}=N | [{'(', _} | _]=Ts], Opt) when Type =:= atom; Type =:= var -> %% minus, macro and open parenthesis at start of form - assume that @@ -657,6 +680,11 @@ scan_form([{'?', L}, {Type, _, _}=N | [{'(', _} | _]=Ts], Opt) scan_form(Ts, Opt) -> scan_macros(Ts, Opt). +build_info_string(Prefix, Ts0) -> + Ts = lists:droplast(Ts0), + String = lists:droplast(tokens_to_string(Ts)), + Prefix ++ " " ++ String ++ ".". + scan_macros(Ts, Opt) -> scan_macros(Ts, [], Opt). @@ -865,6 +893,10 @@ tokens_to_string([]) -> format_error(macro_args) -> errormsg("macro call missing end parenthesis"); +format_error({error, Error}) -> + Error; +format_error({warning, Error}) -> + Error; format_error({unknown, Reason}) -> errormsg(io_lib:format("unknown error: ~tP", [Reason, 15])). diff --git a/lib/syntax_tools/src/erl_prettypr.erl b/lib/syntax_tools/src/erl_prettypr.erl index 60a15c8e3f..6906ef1553 100644 --- a/lib/syntax_tools/src/erl_prettypr.erl +++ b/lib/syntax_tools/src/erl_prettypr.erl @@ -675,7 +675,12 @@ lay_2(Node, Ctxt) -> %% attribute name, without following parentheses. Ctxt1 = reset_prec(Ctxt), Args = erl_syntax:attribute_arguments(Node), - N = erl_syntax:attribute_name(Node), + N = case erl_syntax:attribute_name(Node) of + {atom, _, 'if'} -> + erl_syntax:variable('if'); + N0 -> + N0 + end, D = case attribute_type(Node) of spec -> [SpecTuple] = Args, diff --git a/lib/syntax_tools/src/erl_syntax_lib.erl b/lib/syntax_tools/src/erl_syntax_lib.erl index c7f477c4d2..ced0dba3e2 100644 --- a/lib/syntax_tools/src/erl_syntax_lib.erl +++ b/lib/syntax_tools/src/erl_syntax_lib.erl @@ -1317,6 +1317,8 @@ analyze_attribute(Node) -> include_lib -> preprocessor; ifdef -> preprocessor; ifndef -> preprocessor; + 'if' -> preprocessor; + elif -> preprocessor; else -> preprocessor; endif -> preprocessor; A -> -- cgit v1.2.3 From 46237d41e7455ae5801d78e85a82216b73697f44 Mon Sep 17 00:00:00 2001 From: Tomas Abrahamsson Date: Wed, 9 May 2018 00:20:53 +0200 Subject: macros.xml: Document ?OTP_RELEASE, -if and -elif --- system/doc/reference_manual/macros.xml | 35 ++++++++++++++++++++++++++++++++-- 1 file changed, 33 insertions(+), 2 deletions(-) diff --git a/system/doc/reference_manual/macros.xml b/system/doc/reference_manual/macros.xml index a341307ab7..760599308c 100644 --- a/system/doc/reference_manual/macros.xml +++ b/system/doc/reference_manual/macros.xml @@ -150,6 +150,11 @@ bar(X) -> The name of the current function. ?FUNCTION_ARITY The arity (number of arguments) for the current function. + ?OTP_RELEASE + The OTP release that the currently executing ERTS + application is part of, as an integer. For details, see + erlang:system_info(otp_release). + This macro was introduced in OTP release 21. @@ -202,8 +207,16 @@ f() -> directive. If that condition is false, the lines following else are evaluated instead. -endif. - Specifies the end of an ifdef or ifndef - directive. + Specifies the end of an ifdef, an ifndef + directive, or the end of an if or elif directive. + -if(Condition). + Evaluates the following lines only if Condition + evaluates to true. + -elif(Condition). + Only allowed after an if or another elif directive. + If the preceding if or elif directives do not + evaluate to true, and the Condition evaluates to true, + the lines following the elif are evaluated instead.

The macro directives cannot be used inside functions.

@@ -231,6 +244,24 @@ or {ok,m}

?LOG(Arg) is then expanded to a call to io:format/2 and provide the user with some simple trace output.

+ +

Example:

+ +-module(m) +... +-ifdef(OTP_RELEASE). + %% OTP 21 or higher + -if(?OTP_RELEASE >= 22). + %% Code that will work in OTP 22 or higher + -elif(?OTP_RELEASE >= 21). + %% Code that will work in OTP 21 or higher + -endif. +-else. + %% OTP 20 or lower. +-endif. +... +

The code uses the OTP_RELEASE macro to conditionally + select code depending on release.

-- cgit v1.2.3