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Flow analysis: replace context toString methods with a less fragile m…
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…echanism.

Adds getters `_debugFields` and `_debugType` to the `_FlowContext`
base class, and adds a single implementation of
`_FlowContext.toString` that builds a representation of the context
based on them.  This replaces the implementations of `toString` in all
the classes derived from `_FlowContext`, which were more difficult to
get right and keep synchronized with code changes.

Also changes `_TryFinallyContext` from a `late final` variable to a
nullable variable.  This sacrifices a tiny bit of safety, but has the
advantage of allowing `toString` to show the value if it's been
initialized, and avoid crashing if it hasn't.

Change-Id: I0ca3ddfed21934c54eaba912c84edda79c8eadfc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/276202
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Paul Berry <[email protected]>
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@stereotype441
stereotype441 authored and Commit Queue committed Jan 3, 2023
1 parent 8e1f576 commit e64c60d
Showing 1 changed file with 131 additions and 43 deletions.
174 changes: 131 additions & 43 deletions pkg/_fe_analyzer_shared/lib/src/flow_analysis/flow_analysis.dart
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Original file line number Diff line number Diff line change
Expand Up @@ -3261,8 +3261,11 @@ class _AssertContext<Type extends Object> extends _SimpleContext<Type> {
_AssertContext(super.previous);

@override
String toString() =>
'_AssertContext(previous: $_previous, conditionInfo: $_conditionInfo)';
Map<String, Object?> get _debugFields =>
super._debugFields..['conditionInfo'] = _conditionInfo;

@override
String get _debugType => '_AssertContext';
}

/// [_FlowContext] representing a language construct that branches on a boolean
Expand All @@ -3275,7 +3278,11 @@ class _BranchContext<Type extends Object> extends _FlowContext {
_BranchContext(this._branchModel);

@override
String toString() => '_BranchContext(branchModel: $_branchModel)';
Map<String, Object?> get _debugFields =>
super._debugFields..['branchModel'] = _branchModel;

@override
String get _debugType => '_BranchContext';
}

/// [_FlowContext] representing a language construct that can be targeted by
Expand All @@ -3298,8 +3305,13 @@ class _BranchTargetContext<Type extends Object> extends _FlowContext {
_BranchTargetContext(this._checkpoint);

@override
String toString() => '_BranchTargetContext(breakModel: $_breakModel, '
'continueModel: $_continueModel, checkpoint: $_checkpoint)';
Map<String, Object?> get _debugFields => super._debugFields
..['breakModel'] = _breakModel
..['continueModel'] = _continueModel
..['checkpoint'] = _checkpoint;

@override
String get _debugType => '_BranchTargetContext';
}

/// [_FlowContext] representing a conditional expression.
Expand All @@ -3311,8 +3323,11 @@ class _ConditionalContext<Type extends Object> extends _BranchContext<Type> {
_ConditionalContext(super._branchModel);

@override
String toString() => '_ConditionalContext(branchModel: $_branchModel, '
'thenInfo: $_thenInfo)';
Map<String, Object?> get _debugFields =>
super._debugFields..['thenInfo'] = _thenInfo;

@override
String get _debugType => '_ConditionalContext';
}

/// Data structure representing the result of demoting a variable from one type
Expand Down Expand Up @@ -4320,7 +4335,7 @@ class _FlowAnalysisImpl<Node extends Object, Statement extends Node,
_TryFinallyContext<Type> context =
_stack.removeLast() as _TryFinallyContext<Type>;
_current = context._afterBodyAndCatches!
.attachFinally(operations, context._beforeFinally, _current);
.attachFinally(operations, context._beforeFinally!, _current);
}

@override
Expand Down Expand Up @@ -4660,15 +4675,51 @@ class _FlowAnalysisImpl<Node extends Object, Statement extends Node,

/// Base class for objects representing constructs in the Dart programming
/// language for which flow analysis information needs to be tracked.
abstract class _FlowContext {}
abstract class _FlowContext {
_FlowContext() {
assert(() {
// Check that `_debugType` has been overridden in a way that reflects the
// class name. Note that this assumes the behavior of `runtimeType` in
// the VM, but that's ok, because this code is only active when asserts
// are enabled, and we only run unit tests on the VM.
String expectedDebugType = runtimeType.toString();
int lessThanIndex = expectedDebugType.indexOf('<');
if (lessThanIndex > 0) {
expectedDebugType = expectedDebugType.substring(0, lessThanIndex);
}
assert(_debugType == expectedDebugType,
'Expected a debug type of $expectedDebugType, got $_debugType');
return true;
}());
}

/// Returns a freshly allocated map whose keys are the names of fields in the
/// class, and whose values are the values of those fields.
///
/// This is used by [toString] to print out information for debugging.
Map<String, Object?> get _debugFields => {};

/// Returns a string representation of the class name. This is used by
/// [toString] to print out information for debugging.
String get _debugType;

@override
String toString() {
List<String> fields = [
for (MapEntry<String, Object?> entry in _debugFields.entries)
if (entry.value != null) '${entry.key}: ${entry.value}'
];
return '$_debugType(${fields.join(', ')})';
}
}

/// [_FlowContext] representing a function expression.
class _FunctionExpressionContext<Type extends Object>
extends _SimpleContext<Type> {
_FunctionExpressionContext(super.previous);

@override
String toString() => '_FunctionExpressionContext(previous: $_previous)';
String get _debugType => '_FunctionExpressionContext';
}

/// [_FlowContext] representing an `if` statement.
Expand All @@ -4680,8 +4731,11 @@ class _IfContext<Type extends Object> extends _BranchContext<Type> {
_IfContext(super._branchModel);

@override
String toString() =>
'_IfContext(branchModel: $_branchModel, afterThen: $_afterThen)';
Map<String, Object?> get _debugFields =>
super._debugFields..['afterThen'] = _afterThen;

@override
String get _debugType => '_IfContext';
}

/// [_FlowContext] representing an "if-null" (`??`) expression.
Expand All @@ -4693,7 +4747,11 @@ class _IfNullExpressionContext<Type extends Object> extends _FlowContext {
_IfNullExpressionContext(this._shortcutState);

@override
String toString() => '_IfNullExpressionContext($_shortcutState)';
Map<String, Object?> get _debugFields =>
super._debugFields..['shortcutState'] = _shortcutState;

@override
String get _debugType => '_IfNullExpressionContext';
}

/// Contextual information tracked by legacy type promotion about a binary "and"
Expand Down Expand Up @@ -5346,7 +5404,7 @@ class _NullAwareAccessContext<Type extends Object>
_NullAwareAccessContext(super.previous);

@override
String toString() => '_NullAwareAccessContext(previous: $_previous)';
String get _debugType => '_NullAwareAccessContext';
}

/// [ExpressionInfo] representing a `null` literal.
Expand Down Expand Up @@ -5392,10 +5450,12 @@ class _OrPatternContext<Type extends Object> extends _PatternContext<Type> {
this._previousUnmatched);

@override
String toString() =>
'_OrPatternContext(matchedValueReference: $_matchedValueReference, '
'matchedValueType: $_matchedValueType, '
'previousUnmatched: $_previousUnmatched, lhsMatched: $_lhsMatched)';
Map<String, Object?> get _debugFields => super._debugFields
..['previousUnmatched'] = _previousUnmatched
..['lhsMatched'] = _lhsMatched;

@override
String get _debugType => '_OrPatternContext';
}

/// [_FlowContext] representing a pattern.
Expand All @@ -5409,9 +5469,12 @@ class _PatternContext<Type extends Object> extends _FlowContext {
_PatternContext(this._matchedValueReference, this._matchedValueType);

@override
String toString() =>
'_PatternContext(matchedValueReference: $_matchedValueReference, '
'matchedValueType: $_matchedValueType)';
Map<String, Object?> get _debugFields => super._debugFields
..['matchedValueReference'] = _matchedValueReference
..['matchedValueType'] = _matchedValueType;

@override
String get _debugType => '_PatternContext';
}

/// [ReferenceWithType] object representing a property get.
Expand Down Expand Up @@ -5451,10 +5514,13 @@ class _ScrutineeContext<Type extends Object> extends _FlowContext {
required this.previousScrutineeType});

@override
String toString() => '_ScrutineeContext('
'previousScrutineeReference: $previousScrutineeReference, '
'previousScrutineeSsaNode: $previousScrutineeSsaNode, '
'previousScrutineeType: $previousScrutineeType)';
Map<String, Object?> get _debugFields => super._debugFields
..['previousScrutineeReference'] = previousScrutineeReference
..['previousScrutineeSsaNode'] = previousScrutineeSsaNode
..['previousScrutineeType'] = previousScrutineeType;

@override
String get _debugType => '_ScrutineeContext';
}

/// [_FlowContext] representing a language construct for which flow analysis
Expand All @@ -5467,6 +5533,10 @@ abstract class _SimpleContext<Type extends Object> extends _FlowContext {
final FlowModel<Type> _previous;

_SimpleContext(this._previous);

@override
Map<String, Object?> get _debugFields =>
super._debugFields..['previous'] = _previous;
}

/// [_FlowContext] representing a language construct that can be targeted by
Expand All @@ -5483,9 +5553,11 @@ class _SimpleStatementContext<Type extends Object>
_SimpleStatementContext(super.checkpoint, this._previous);

@override
String toString() => '_SimpleStatementContext(breakModel: $_breakModel, '
'continueModel: $_continueModel, previous: $_previous, '
'checkpoint: $_checkpoint)';
Map<String, Object?> get _debugFields =>
super._debugFields..['previous'] = _previous;

@override
String get _debugType => '_SimpleStatementContext';
}

class _SwitchAlternativesContext<Type extends Object> extends _FlowContext {
Expand All @@ -5496,8 +5568,12 @@ class _SwitchAlternativesContext<Type extends Object> extends _FlowContext {
_SwitchAlternativesContext(this._previous);

@override
String toString() => '_SwitchAlternativesContext(previous: $_previous, '
'combinedModel: $_combinedModel)';
Map<String, Object?> get _debugFields => super._debugFields
..['previous'] = _previous
..['combinedModel'] = _combinedModel;

@override
String get _debugType => '_SwitchAlternativesContext';
}

/// [_FlowContext] representing a switch statement.
Expand All @@ -5510,19 +5586,19 @@ class _SwitchStatementContext<Type extends Object>
super.checkpoint, super._previous, this._scrutineeType);

@override
String toString() => '_SwitchStatementContext(breakModel: $_breakModel, '
'continueModel: $_continueModel, previous: $_previous, '
'checkpoint: $_checkpoint, scrutineeType: $_scrutineeType)';
Map<String, Object?> get _debugFields =>
super._debugFields..['scrutineeType'] = _scrutineeType;

@override
String get _debugType => '_SwitchStatementContext';
}

/// [_FlowContext] representing the top level of a pattern syntax tree.
class _TopPatternContext<Type extends Object> extends _PatternContext<Type> {
_TopPatternContext(super._matchedValueReference, super.matchedValueType);

@override
String toString() =>
'_TopPatternContext(matchedValueReference: $_matchedValueReference, '
'matchedValueType: $_matchedValueType)';
String get _debugType => '_TopPatternContext';
}

/// Specialization of [ExpressionInfo] for the case where the information we
Expand Down Expand Up @@ -5566,17 +5642,27 @@ class _TryContext<Type extends Object> extends _SimpleContext<Type> {
_TryContext(super.previous);

@override
String toString() =>
'_TryContext(previous: $_previous, beforeCatch: $_beforeCatch, '
'afterBodyAndCatches: $_afterBodyAndCatches)';
Map<String, Object?> get _debugFields => super._debugFields
..['beforeCatch'] = _beforeCatch
..['afterBodyAndCatches'] = '_afterBodyAndCatches';

@override
String get _debugType => '_TryContext';
}

class _TryFinallyContext<Type extends Object> extends _TryContext<Type> {
/// The flow model representing program state at the top of the `finally`
/// block.
late final FlowModel<Type> _beforeFinally;
FlowModel<Type>? _beforeFinally;

_TryFinallyContext(super.previous);

@override
Map<String, Object?> get _debugFields =>
super._debugFields..['beforeFinally'] = _beforeFinally;

@override
String get _debugType => '_TryFinallyContext';
}

/// [_FlowContext] representing a `while` loop (or a C-style `for` loop, which
Expand All @@ -5588,7 +5674,9 @@ class _WhileContext<Type extends Object> extends _BranchTargetContext<Type> {
_WhileContext(super.checkpoint, this._conditionInfo);

@override
String toString() => '_WhileContext(breakModel: $_breakModel, '
'continueModel: $_continueModel, conditionInfo: $_conditionInfo, '
'checkpoint: $_checkpoint)';
Map<String, Object?> get _debugFields =>
super._debugFields..['conditionInfo'] = _conditionInfo;

@override
String get _debugType => '_WhileContext';
}

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