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Fix parsing of PATTERN as T? when
The logic for parsing types has special disambiguation rules for deciding whether a trailing `?` should be included in the type, based on what token(s) follow the `?`. In the case where the token that follows the `?` is `when`, we need to look further ahead to disambiguate, to distinguish `PATTERN as T? when guard` from something like `EXPRESSION is T ? when : otherwise`. (Note: an alternative implementation would be to disambiguate based on whether we're parsing a pattern or an expression. But in the future I want to move toward an architecture where expression parsing and pattern parsing are combined, so that if the parser makes the wrong decision about whether it's looking at a pattern or an expression, error recovery will do a better job. So I'm disambiguating based solely on what follows the `?`.) Bug: #50035 Change-Id: Idbc780b7b54fecc7fd01cae868c34771564dd804 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/292282 Commit-Queue: Paul Berry <[email protected]> Reviewed-by: Jens Johansen <[email protected]>
1 parent e6d352d commit 452dcdf

13 files changed

+564
-4
lines changed

‎pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart

Lines changed: 8 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -7578,11 +7578,15 @@ class Parser {
75787578
// rather than the start of a conditional expression.
75797579
return typeInfo;
75807580
}
7581-
if (optional('{', next)) {
7581+
if (optional('{', next) || optional('when', next)) {
75827582
// <expression> is/as <type> ? {
7583-
// This could be either a nullable type (e.g. last initializer in a
7584-
// constructor with a body), or a non-nullable type and a conditional.
7585-
// As with "?[" we check and have it as a conditional if it can be.
7583+
// This could be either a nullable type (e.g. last initializer in a
7584+
// constructor with a body), or a non-nullable type and a conditional.
7585+
// <expression> is/as <type> ? when
7586+
// This could be either a nullable type (e.g. a cast pattern followed
7587+
// by a guard), or a non-nullable type and a conditional (where the
7588+
// first token of the "then" expression is the identifier `when`).
7589+
// If it can be successfully parsed as a conditional, we do so.
75867590
bool isConditional = canParseAsConditional(skipToken);
75877591
if (!isConditional) {
75887592
return typeInfo;

‎pkg/analyzer/test/generated/patterns_parser_test.dart

Lines changed: 67 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -8296,6 +8296,73 @@ SwitchExpression
82968296
''');
82978297
}
82988298

8299+
test_typeQuestionBeforeWhen_conditional() {
8300+
// The logic for parsing types has special disambiguation rules for deciding
8301+
// whether a trailing `?` should be included in the type; these rules are
8302+
// based primarily on what token(s) follow the `?`. Make sure that these
8303+
// rules do the right thing if the token that follows the `?` is `when`, but
8304+
// the `when` is an ordinary identifier.
8305+
_parse('''
8306+
void f(condition, when, otherwise) => condition as bool ? when : otherwise;
8307+
''');
8308+
var node = findNode.functionDeclaration('=>').functionExpression.body;
8309+
assertParsedNodeText(node, r'''
8310+
ExpressionFunctionBody
8311+
functionDefinition: =>
8312+
expression: ConditionalExpression
8313+
condition: AsExpression
8314+
expression: SimpleIdentifier
8315+
token: condition
8316+
asOperator: as
8317+
type: NamedType
8318+
name: SimpleIdentifier
8319+
token: bool
8320+
question: ?
8321+
thenExpression: SimpleIdentifier
8322+
token: when
8323+
colon: :
8324+
elseExpression: SimpleIdentifier
8325+
token: otherwise
8326+
semicolon: ;
8327+
''');
8328+
}
8329+
8330+
test_typeQuestionBeforeWhen_guard() {
8331+
// The logic for parsing types has special disambiguation rules for deciding
8332+
// whether a trailing `?` should be included in the type; these rules are
8333+
// based primarily on what token(s) follow the `?`. Make sure that these
8334+
// rules do the right thing if the token that follows the `?` is the `when`
8335+
// of a pattern guard.
8336+
_parse('''
8337+
void f(x) {
8338+
switch (x) {
8339+
case _ as int? when x == null:
8340+
break;
8341+
}
8342+
}
8343+
''');
8344+
var node = findNode.singleGuardedPattern;
8345+
assertParsedNodeText(node, r'''
8346+
GuardedPattern
8347+
pattern: CastPattern
8348+
pattern: WildcardPattern
8349+
name: _
8350+
asToken: as
8351+
type: NamedType
8352+
name: SimpleIdentifier
8353+
token: int
8354+
question: ?
8355+
whenClause: WhenClause
8356+
whenKeyword: when
8357+
expression: BinaryExpression
8358+
leftOperand: SimpleIdentifier
8359+
token: x
8360+
operator: ==
8361+
rightOperand: NullLiteral
8362+
literal: null
8363+
''');
8364+
}
8365+
82998366
test_variable_bare_insideCast() {
83008367
_parse('''
83018368
void f(x) {

‎pkg/front_end/parser_testcases/patterns/typeQuestionBeforeWhen_conditional.dart

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1 @@
1+
void f(condition, when, otherwise) => condition as bool ? when : otherwise;

‎pkg/front_end/parser_testcases/patterns/typeQuestionBeforeWhen_conditional.dart.expect

Lines changed: 57 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,57 @@
1+
beginCompilationUnit(void)
2+
beginMetadataStar(void)
3+
endMetadataStar(0)
4+
beginTopLevelMember(void)
5+
beginTopLevelMethod(, null, null)
6+
handleVoidKeyword(void)
7+
handleIdentifier(f, topLevelFunctionDeclaration)
8+
handleNoTypeVariables(()
9+
beginFormalParameters((, MemberKind.TopLevelMethod)
10+
beginMetadataStar(condition)
11+
endMetadataStar(0)
12+
beginFormalParameter(condition, MemberKind.TopLevelMethod, null, null, null)
13+
handleNoType(()
14+
handleIdentifier(condition, formalParameterDeclaration)
15+
handleFormalParameterWithoutValue(,)
16+
endFormalParameter(null, null, null, condition, null, null, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
17+
beginMetadataStar(when)
18+
endMetadataStar(0)
19+
beginFormalParameter(when, MemberKind.TopLevelMethod, null, null, null)
20+
handleNoType(,)
21+
handleIdentifier(when, formalParameterDeclaration)
22+
handleFormalParameterWithoutValue(,)
23+
endFormalParameter(null, null, null, when, null, null, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
24+
beginMetadataStar(otherwise)
25+
endMetadataStar(0)
26+
beginFormalParameter(otherwise, MemberKind.TopLevelMethod, null, null, null)
27+
handleNoType(,)
28+
handleIdentifier(otherwise, formalParameterDeclaration)
29+
handleFormalParameterWithoutValue())
30+
endFormalParameter(null, null, null, otherwise, null, null, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
31+
endFormalParameters(3, (, ), MemberKind.TopLevelMethod)
32+
handleAsyncModifier(null, null)
33+
handleIdentifier(condition, expression)
34+
handleNoTypeArguments(as)
35+
handleNoArguments(as)
36+
handleSend(condition, as)
37+
beginAsOperatorType(as)
38+
handleIdentifier(bool, typeReference)
39+
handleNoTypeArguments(?)
40+
handleType(bool, null)
41+
endAsOperatorType(as)
42+
handleAsOperator(as)
43+
beginConditionalExpression(?)
44+
handleIdentifier(when, expression)
45+
handleNoTypeArguments(:)
46+
handleNoArguments(:)
47+
handleSend(when, :)
48+
handleConditionalExpressionColon()
49+
handleIdentifier(otherwise, expression)
50+
handleNoTypeArguments(;)
51+
handleNoArguments(;)
52+
handleSend(otherwise, ;)
53+
endConditionalExpression(?, :)
54+
handleExpressionFunctionBody(=>, ;)
55+
endTopLevelMethod(void, null, ;)
56+
endTopLevelDeclaration()
57+
endCompilationUnit(1, )

‎pkg/front_end/parser_testcases/patterns/typeQuestionBeforeWhen_conditional.dart.intertwined.expect

Lines changed: 144 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,144 @@
1+
parseUnit(void)
2+
skipErrorTokens(void)
3+
listener: beginCompilationUnit(void)
4+
syntheticPreviousToken(void)
5+
parseTopLevelDeclarationImpl(, Instance of 'DirectiveContext')
6+
parseMetadataStar()
7+
listener: beginMetadataStar(void)
8+
listener: endMetadataStar(0)
9+
parseTopLevelMemberImpl()
10+
listener: beginTopLevelMember(void)
11+
parseTopLevelMethod(, null, null, , Instance of 'VoidType', null, f, false)
12+
listener: beginTopLevelMethod(, null, null)
13+
listener: handleVoidKeyword(void)
14+
ensureIdentifierPotentiallyRecovered(void, topLevelFunctionDeclaration, false)
15+
listener: handleIdentifier(f, topLevelFunctionDeclaration)
16+
parseMethodTypeVar(f)
17+
listener: handleNoTypeVariables(()
18+
parseGetterOrFormalParameters(f, f, false, MemberKind.TopLevelMethod)
19+
parseFormalParameters(f, MemberKind.TopLevelMethod)
20+
parseFormalParametersRest((, MemberKind.TopLevelMethod)
21+
listener: beginFormalParameters((, MemberKind.TopLevelMethod)
22+
parseFormalParameter((, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
23+
parseMetadataStar(()
24+
listener: beginMetadataStar(condition)
25+
listener: endMetadataStar(0)
26+
listener: beginFormalParameter(condition, MemberKind.TopLevelMethod, null, null, null)
27+
listener: handleNoType(()
28+
ensureIdentifier((, formalParameterDeclaration)
29+
listener: handleIdentifier(condition, formalParameterDeclaration)
30+
listener: handleFormalParameterWithoutValue(,)
31+
listener: endFormalParameter(null, null, null, condition, null, null, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
32+
parseFormalParameter(,, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
33+
parseMetadataStar(,)
34+
listener: beginMetadataStar(when)
35+
listener: endMetadataStar(0)
36+
listener: beginFormalParameter(when, MemberKind.TopLevelMethod, null, null, null)
37+
listener: handleNoType(,)
38+
ensureIdentifier(,, formalParameterDeclaration)
39+
inPlainSync()
40+
listener: handleIdentifier(when, formalParameterDeclaration)
41+
listener: handleFormalParameterWithoutValue(,)
42+
listener: endFormalParameter(null, null, null, when, null, null, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
43+
parseFormalParameter(,, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
44+
parseMetadataStar(,)
45+
listener: beginMetadataStar(otherwise)
46+
listener: endMetadataStar(0)
47+
listener: beginFormalParameter(otherwise, MemberKind.TopLevelMethod, null, null, null)
48+
listener: handleNoType(,)
49+
ensureIdentifier(,, formalParameterDeclaration)
50+
listener: handleIdentifier(otherwise, formalParameterDeclaration)
51+
listener: handleFormalParameterWithoutValue())
52+
listener: endFormalParameter(null, null, null, otherwise, null, null, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
53+
listener: endFormalParameters(3, (, ), MemberKind.TopLevelMethod)
54+
parseAsyncModifierOpt())
55+
listener: handleAsyncModifier(null, null)
56+
inPlainSync()
57+
parseFunctionBody(), false, false)
58+
parseExpressionFunctionBody(=>, false)
59+
parseExpression(=>)
60+
looksLikeOuterPatternEquals(=>)
61+
skipOuterPattern(=>)
62+
skipObjectPatternRest(condition)
63+
parsePrecedenceExpression(=>, 1, true, ConstantPatternContext.none)
64+
parseUnaryExpression(=>, true, ConstantPatternContext.none)
65+
parsePrimary(=>, expression, ConstantPatternContext.none)
66+
parseSendOrFunctionLiteral(=>, expression, ConstantPatternContext.none)
67+
parseSend(=>, expression, ConstantPatternContext.none)
68+
isNextIdentifier(=>)
69+
ensureIdentifier(=>, expression)
70+
listener: handleIdentifier(condition, expression)
71+
listener: handleNoTypeArguments(as)
72+
parseArgumentsOpt(condition)
73+
listener: handleNoArguments(as)
74+
listener: handleSend(condition, as)
75+
parseAsOperatorRest(condition)
76+
listener: beginAsOperatorType(as)
77+
computeTypeAfterIsOrAs(as)
78+
canParseAsConditional(?)
79+
parseExpressionWithoutCascade(?)
80+
parsePrecedenceExpression(?, 1, false, ConstantPatternContext.none)
81+
parseUnaryExpression(?, false, ConstantPatternContext.none)
82+
parsePrimary(?, expression, ConstantPatternContext.none)
83+
inPlainSync()
84+
parseSendOrFunctionLiteral(?, expression, ConstantPatternContext.none)
85+
parseSend(?, expression, ConstantPatternContext.none)
86+
isNextIdentifier(?)
87+
ensureIdentifier(?, expression)
88+
inPlainSync()
89+
parseArgumentsOpt(when)
90+
parseExpressionWithoutCascade(:)
91+
parsePrecedenceExpression(:, 1, false, ConstantPatternContext.none)
92+
parseUnaryExpression(:, false, ConstantPatternContext.none)
93+
parsePrimary(:, expression, ConstantPatternContext.none)
94+
parseSendOrFunctionLiteral(:, expression, ConstantPatternContext.none)
95+
parseSend(:, expression, ConstantPatternContext.none)
96+
isNextIdentifier(:)
97+
ensureIdentifier(:, expression)
98+
parseArgumentsOpt(otherwise)
99+
listener: handleIdentifier(bool, typeReference)
100+
listener: handleNoTypeArguments(?)
101+
listener: handleType(bool, null)
102+
listener: endAsOperatorType(as)
103+
listener: handleAsOperator(as)
104+
skipChainedAsIsOperators(bool)
105+
parseConditionalExpressionRest(bool)
106+
listener: beginConditionalExpression(?)
107+
parseExpressionWithoutCascade(?)
108+
parsePrecedenceExpression(?, 1, false, ConstantPatternContext.none)
109+
parseUnaryExpression(?, false, ConstantPatternContext.none)
110+
parsePrimary(?, expression, ConstantPatternContext.none)
111+
inPlainSync()
112+
parseSendOrFunctionLiteral(?, expression, ConstantPatternContext.none)
113+
parseSend(?, expression, ConstantPatternContext.none)
114+
isNextIdentifier(?)
115+
ensureIdentifier(?, expression)
116+
inPlainSync()
117+
listener: handleIdentifier(when, expression)
118+
listener: handleNoTypeArguments(:)
119+
parseArgumentsOpt(when)
120+
listener: handleNoArguments(:)
121+
listener: handleSend(when, :)
122+
ensureColon(when)
123+
listener: handleConditionalExpressionColon()
124+
parseExpressionWithoutCascade(:)
125+
parsePrecedenceExpression(:, 1, false, ConstantPatternContext.none)
126+
parseUnaryExpression(:, false, ConstantPatternContext.none)
127+
parsePrimary(:, expression, ConstantPatternContext.none)
128+
parseSendOrFunctionLiteral(:, expression, ConstantPatternContext.none)
129+
parseSend(:, expression, ConstantPatternContext.none)
130+
isNextIdentifier(:)
131+
ensureIdentifier(:, expression)
132+
listener: handleIdentifier(otherwise, expression)
133+
listener: handleNoTypeArguments(;)
134+
parseArgumentsOpt(otherwise)
135+
listener: handleNoArguments(;)
136+
listener: handleSend(otherwise, ;)
137+
listener: endConditionalExpression(?, :)
138+
ensureSemicolon(otherwise)
139+
listener: handleExpressionFunctionBody(=>, ;)
140+
inGenerator()
141+
listener: endTopLevelMethod(void, null, ;)
142+
listener: endTopLevelDeclaration()
143+
reportAllErrorTokens(void)
144+
listener: endCompilationUnit(1, )

‎pkg/front_end/parser_testcases/patterns/typeQuestionBeforeWhen_conditional.dart.parser.expect

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
1+
void f(condition, when, otherwise) => condition as bool ? when : otherwise;
2+
3+
4+
void[KeywordToken] f[StringToken]([BeginToken]condition[StringToken],[SimpleToken] when[KeywordToken],[SimpleToken] otherwise[StringToken])[SimpleToken] =>[SimpleToken] condition[StringToken] as[KeywordToken] bool[StringToken] ?[SimpleToken] when[KeywordToken] :[SimpleToken] otherwise[StringToken];[SimpleToken]
5+
[SimpleToken]

‎pkg/front_end/parser_testcases/patterns/typeQuestionBeforeWhen_conditional.dart.scanner.expect

Lines changed: 5 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
1+
void f(condition, when, otherwise) => condition as bool ? when : otherwise;
2+
3+
4+
void[KeywordToken] f[StringToken]([BeginToken]condition[StringToken],[SimpleToken] when[KeywordToken],[SimpleToken] otherwise[StringToken])[SimpleToken] =>[SimpleToken] condition[StringToken] as[KeywordToken] bool[StringToken] ?[SimpleToken] when[KeywordToken] :[SimpleToken] otherwise[StringToken];[SimpleToken]
5+
[SimpleToken]

‎pkg/front_end/parser_testcases/patterns/typeQuestionBeforeWhen_guard.dart

Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,6 @@
1+
void f(x) {
2+
switch (x) {
3+
case _ as int? when x == null:
4+
break;
5+
}
6+
}

‎pkg/front_end/parser_testcases/patterns/typeQuestionBeforeWhen_guard.dart.expect

Lines changed: 54 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,54 @@
1+
beginCompilationUnit(void)
2+
beginMetadataStar(void)
3+
endMetadataStar(0)
4+
beginTopLevelMember(void)
5+
beginTopLevelMethod(, null, null)
6+
handleVoidKeyword(void)
7+
handleIdentifier(f, topLevelFunctionDeclaration)
8+
handleNoTypeVariables(()
9+
beginFormalParameters((, MemberKind.TopLevelMethod)
10+
beginMetadataStar(x)
11+
endMetadataStar(0)
12+
beginFormalParameter(x, MemberKind.TopLevelMethod, null, null, null)
13+
handleNoType(()
14+
handleIdentifier(x, formalParameterDeclaration)
15+
handleFormalParameterWithoutValue())
16+
endFormalParameter(null, null, null, x, null, null, FormalParameterKind.requiredPositional, MemberKind.TopLevelMethod)
17+
endFormalParameters(1, (, ), MemberKind.TopLevelMethod)
18+
handleAsyncModifier(null, null)
19+
beginBlockFunctionBody({)
20+
beginSwitchStatement(switch)
21+
handleIdentifier(x, expression)
22+
handleNoTypeArguments())
23+
handleNoArguments())
24+
handleSend(x, ))
25+
handleParenthesizedCondition((, null, null)
26+
beginSwitchBlock({)
27+
beginCaseExpression(case)
28+
handleNoType(_)
29+
handleWildcardPattern(null, _)
30+
beginAsOperatorType(as)
31+
handleIdentifier(int, typeReference)
32+
handleNoTypeArguments(?)
33+
handleType(int, ?)
34+
endAsOperatorType(as)
35+
handleCastPattern(as)
36+
beginSwitchCaseWhenClause(when)
37+
handleIdentifier(x, expression)
38+
handleNoTypeArguments(==)
39+
handleNoArguments(==)
40+
handleSend(x, ==)
41+
beginBinaryExpression(==)
42+
handleLiteralNull(null)
43+
endBinaryExpression(==)
44+
endSwitchCaseWhenClause(null)
45+
endCaseExpression(case, when, :)
46+
beginSwitchCase(0, 1, case)
47+
handleBreakStatement(false, break, ;)
48+
endSwitchCase(0, 1, null, null, 1, case, })
49+
endSwitchBlock(1, {, })
50+
endSwitchStatement(switch, })
51+
endBlockFunctionBody(1, {, })
52+
endTopLevelMethod(void, null, })
53+
endTopLevelDeclaration()
54+
endCompilationUnit(1, )

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