Fix crash in GetDeconstructionInfo#27605
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jcouv merged 1 commit intodotnet:masterfrom Jun 8, 2018
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cston
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Jun 8, 2018
AlekseyTs
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Jun 8, 2018
| { | ||
| static void M(string s) | ||
| { | ||
| foreach (char in s) { } |
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foreach (char in s) { } [](start = 8, length = 23)
I am curious why we are parsing this as ForEachVariableStatement
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Looking at the code (without stepping through it to confirm), here's what I think happens:
- we reach the open paren
- try to parse a declaration expression (
ParseExpressionOrDeclaration) - but
IsPossibleDeclarationExpressionscans ahead of the type to check for a designation (missing, keywordinis found) - having not found a declaration expression, we go down the route of interpreting the
foreachas not-a-simple-foreach, but rather a deconstruction foreach.
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Marking as approved to merge for 15.8 preview 4. |
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Customer scenario
Type an incomplete
foreach (char in s) { }and hover your mouse over thein. The IDE will pop-up an exception dialog or crash.Bugs this fixes
Fixes #27520
Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/628435
Risk
Performance impact
Low. This fix is just adding a null check.
Is this a regression from a previous update?
Yes, this is a regression from 15.7.
Root cause analysis
Although the API (including this underlying bug) was introduced in 15.6, it was only used for Find All References. But in 15.8, I made a change to use this API in QuickInfo, which is much more common, especially on incomplete code.
How was the bug found?
Watson and bug report from a team member