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Merge pull request #11131 from rhendric/rhendric/pipe-operators
libexpr: experimental pipe operators
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commit
6ec123ad6b
10 changed files with 174 additions and 9 deletions
28
doc/manual/rl-next/pipe-operators.md
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28
doc/manual/rl-next/pipe-operators.md
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---
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synopsis: "Add `pipe-operators` experimental feature"
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prs:
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- 11131
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---
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This is a draft implementation of [RFC 0148](https://github.com/NixOS/rfcs/pull/148).
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The `pipe-operators` experimental feature adds [`<|` and `|>` operators][pipe operators] to the Nix language.
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*a* `|>` *b* is equivalent to the function application *b* *a*, and
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*a* `<|` *b* is equivalent to the function application *a* *b*.
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For example:
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```
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nix-repl> 1 |> builtins.add 2 |> builtins.mul 3
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9
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nix-repl> builtins.add 1 <| builtins.mul 2 <| 3
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7
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```
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`<|` and `|>` are right and left associative, respectively, and have lower precedence than any other operator.
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These properties may change in future releases.
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See [the RFC](https://github.com/NixOS/rfcs/pull/148) for more examples and rationale.
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[pipe operators]: @docroot@/language/operators.md#pipe-operators
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@ -26,13 +26,17 @@
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| Logical conjunction (`AND`) | *bool* `&&` *bool* | left | 12 |
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| Logical disjunction (`OR`) | *bool* <code>\|\|</code> *bool* | left | 13 |
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| [Logical implication] | *bool* `->` *bool* | right | 14 |
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| [Pipe operator] (experimental) | *expr* `\|>` *func* | left | 15 |
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| [Pipe operator] (experimental) | *func* `<\|` *expr* | right | 15 |
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[string]: ./types.md#type-string
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[path]: ./types.md#type-path
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[number]: ./types.md#type-float <!-- TODO(@rhendric, #10970): rationalize this -->
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[number]: ./types.md#type-float
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[list]: ./types.md#list
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[attribute set]: ./types.md#attribute-set
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<!-- TODO(@rhendric, #10970): ^ rationalize number -> int/float -->
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## Attribute selection
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> **Syntax**
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@ -176,3 +180,34 @@ Equivalent to `!`*b1* `||` *b2*.
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[Logical implication]: #logical-implication
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## Pipe operators
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- *a* `|>` *b* is equivalent to *b* *a*
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- *a* `<|` *b* is equivalent to *a* *b*
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> **Example**
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>
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> ```
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> nix-repl> 1 |> builtins.add 2 |> builtins.mul 3
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> 9
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>
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> nix-repl> builtins.add 1 <| builtins.mul 2 <| 3
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> 7
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> ```
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> **Warning**
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>
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> This syntax is part of an
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> [experimental feature](@docroot@/contributing/experimental-features.md)
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> and may change in future releases.
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>
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> To use this syntax, make sure the
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> [`pipe-operators` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-pipe-operators)
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> is enabled.
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> For example, include the following in [`nix.conf`](@docroot@/command-ref/conf-file.md):
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>
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> ```
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> extra-experimental-features = pipe-operators
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> ```
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[Pipe operator]: #pipe-operators
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@ -67,6 +67,14 @@ static StringToken unescapeStr(SymbolTable & symbols, char * s, size_t length)
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return {result, size_t(t - result)};
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}
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static void requireExperimentalFeature(const ExperimentalFeature & feature, const Pos & pos)
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{
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if (!experimentalFeatureSettings.isEnabled(feature))
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throw ParseError(ErrorInfo{
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.msg = HintFmt("experimental Nix feature '%1%' is disabled; add '--extra-experimental-features %1%' to enable it", showExperimentalFeature(feature)),
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.pos = pos,
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});
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}
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}
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@ -119,6 +127,12 @@ or { return OR_KW; }
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\-\> { return IMPL; }
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\/\/ { return UPDATE; }
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\+\+ { return CONCAT; }
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\<\| { requireExperimentalFeature(Xp::PipeOperators, state->positions[CUR_POS]);
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return PIPE_FROM;
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}
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\|\> { requireExperimentalFeature(Xp::PipeOperators, state->positions[CUR_POS]);
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return PIPE_INTO;
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}
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{ID} { yylval->id = {yytext, (size_t) yyleng}; return ID; }
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{INT} { errno = 0;
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@ -99,6 +99,14 @@ static void setDocPosition(const LexerState & lexerState, ExprLambda * lambda, P
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}
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}
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static Expr * makeCall(PosIdx pos, Expr * fn, Expr * arg) {
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if (auto e2 = dynamic_cast<ExprCall *>(fn)) {
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e2->args.push_back(arg);
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return fn;
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}
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return new ExprCall(pos, fn, {arg});
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}
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%}
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@ -123,6 +131,7 @@ static void setDocPosition(const LexerState & lexerState, ExprLambda * lambda, P
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%type <e> start expr expr_function expr_if expr_op
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%type <e> expr_select expr_simple expr_app
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%type <e> expr_pipe_from expr_pipe_into
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%type <list> expr_list
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%type <attrs> binds
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%type <formals> formals
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@ -140,6 +149,7 @@ static void setDocPosition(const LexerState & lexerState, ExprLambda * lambda, P
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%token <path> PATH HPATH SPATH PATH_END
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%token <uri> URI
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%token IF THEN ELSE ASSERT WITH LET IN_KW REC INHERIT EQ NEQ AND OR IMPL OR_KW
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%token PIPE_FROM PIPE_INTO /* <| and |> */
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%token DOLLAR_CURLY /* == ${ */
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%token IND_STRING_OPEN IND_STRING_CLOSE
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%token ELLIPSIS
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@ -206,9 +216,21 @@ expr_function
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expr_if
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: IF expr THEN expr ELSE expr { $$ = new ExprIf(CUR_POS, $2, $4, $6); }
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| expr_pipe_from
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| expr_pipe_into
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| expr_op
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;
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expr_pipe_from
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: expr_op PIPE_FROM expr_pipe_from { $$ = makeCall(state->at(@2), $1, $3); }
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| expr_op PIPE_FROM expr_op { $$ = makeCall(state->at(@2), $1, $3); }
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;
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expr_pipe_into
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: expr_pipe_into PIPE_INTO expr_op { $$ = makeCall(state->at(@2), $3, $1); }
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| expr_op PIPE_INTO expr_op { $$ = makeCall(state->at(@2), $3, $1); }
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;
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expr_op
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: '!' expr_op %prec NOT { $$ = new ExprOpNot($2); }
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| '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(state->s.sub), {new ExprInt(0), $2}); }
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@ -233,13 +255,7 @@ expr_op
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;
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expr_app
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: expr_app expr_select {
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if (auto e2 = dynamic_cast<ExprCall *>($1)) {
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e2->args.push_back($2);
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$$ = $1;
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} else
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$$ = new ExprCall(CUR_POS, $1, {$2});
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}
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: expr_app expr_select { $$ = makeCall(CUR_POS, $1, $2); }
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| expr_select
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;
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@ -24,7 +24,7 @@ struct ExperimentalFeatureDetails
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* feature, we either have no issue at all if few features are not added
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* at the end of the list, or a proper merge conflict if they are.
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*/
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constexpr size_t numXpFeatures = 1 + static_cast<size_t>(Xp::VerifiedFetches);
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constexpr size_t numXpFeatures = 1 + static_cast<size_t>(Xp::PipeOperators);
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constexpr std::array<ExperimentalFeatureDetails, numXpFeatures> xpFeatureDetails = {{
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{
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@ -294,6 +294,14 @@ constexpr std::array<ExperimentalFeatureDetails, numXpFeatures> xpFeatureDetails
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)",
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.trackingUrl = "https://github.com/NixOS/nix/milestone/48",
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},
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{
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.tag = Xp::PipeOperators,
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.name = "pipe-operators",
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.description = R"(
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Add `|>` and `<|` operators to the Nix language.
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)",
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.trackingUrl = "https://github.com/NixOS/nix/milestone/55",
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},
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}};
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static_assert(
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@ -35,6 +35,7 @@ enum struct ExperimentalFeature
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ConfigurableImpureEnv,
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MountedSSHStore,
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VerifiedFetches,
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PipeOperators,
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};
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/**
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5
tests/functional/lang/eval-fail-pipe-operators.err.exp
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5
tests/functional/lang/eval-fail-pipe-operators.err.exp
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error: experimental Nix feature 'pipe-operators' is disabled; add '--extra-experimental-features pipe-operators' to enable it
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at /pwd/lang/eval-fail-pipe-operators.nix:1:3:
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1| 1 |> 2
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| ^
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2|
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1
tests/functional/lang/eval-fail-pipe-operators.nix
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1
tests/functional/lang/eval-fail-pipe-operators.nix
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1 |> 2
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@ -34,6 +34,9 @@ int main (int argc, char **argv) {
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setEnv("_NIX_TEST_NO_SANDBOX", "1");
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#endif
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// For pipe operator tests in trivial.cc
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experimentalFeatureSettings.set("experimental-features", "pipe-operators");
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::testing::InitGoogleTest(&argc, argv);
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return RUN_ALL_TESTS();
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}
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@ -182,6 +182,60 @@ namespace nix {
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ASSERT_THAT(v, IsIntEq(15));
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}
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TEST_F(TrivialExpressionTest, forwardPipe) {
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auto v = eval("1 |> builtins.add 2 |> builtins.mul 3");
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ASSERT_THAT(v, IsIntEq(9));
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}
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TEST_F(TrivialExpressionTest, backwardPipe) {
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auto v = eval("builtins.add 1 <| builtins.mul 2 <| 3");
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ASSERT_THAT(v, IsIntEq(7));
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}
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TEST_F(TrivialExpressionTest, forwardPipeEvaluationOrder) {
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auto v = eval("1 |> null |> (x: 2)");
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ASSERT_THAT(v, IsIntEq(2));
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}
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TEST_F(TrivialExpressionTest, backwardPipeEvaluationOrder) {
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auto v = eval("(x: 1) <| null <| 2");
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ASSERT_THAT(v, IsIntEq(1));
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}
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TEST_F(TrivialExpressionTest, differentPipeOperatorsDoNotAssociate) {
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ASSERT_THROW(eval("(x: 1) <| 2 |> (x: 3)"), ParseError);
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}
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TEST_F(TrivialExpressionTest, differentPipeOperatorsParensLeft) {
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auto v = eval("((x: 1) <| 2) |> (x: 3)");
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ASSERT_THAT(v, IsIntEq(3));
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}
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TEST_F(TrivialExpressionTest, differentPipeOperatorsParensRight) {
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auto v = eval("(x: 1) <| (2 |> (x: 3))");
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ASSERT_THAT(v, IsIntEq(1));
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}
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TEST_F(TrivialExpressionTest, forwardPipeLowestPrecedence) {
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auto v = eval("false -> true |> (x: !x)");
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ASSERT_THAT(v, IsFalse());
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}
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TEST_F(TrivialExpressionTest, backwardPipeLowestPrecedence) {
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auto v = eval("(x: !x) <| false -> true");
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ASSERT_THAT(v, IsFalse());
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}
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TEST_F(TrivialExpressionTest, forwardPipeStrongerThanElse) {
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auto v = eval("if true then 1 else 2 |> 3");
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ASSERT_THAT(v, IsIntEq(1));
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}
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TEST_F(TrivialExpressionTest, backwardPipeStrongerThanElse) {
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auto v = eval("if true then 1 else 2 <| 3");
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ASSERT_THAT(v, IsIntEq(1));
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}
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TEST_F(TrivialExpressionTest, bindOr) {
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auto v = eval("{ or = 1; }");
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ASSERT_THAT(v, IsAttrsOfSize(1));
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