Migrate ASTScope to CharSourceRanges #34207
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SourceRanges behave funny with string interpolation. A SourceRange always spans at least one token, and the end location points at the beginning of the last token that is part of the source range.
Since string literals and string interpolations are always a single token, a SourceRange that ends on a string interpolation will point at the beginning of the string interpolation. However, any source locations of expressions inside the interpolation itself now point into the middle of the string interpolation token. Eg, consider this code:
The source range of the initializer expression for
var xconsists of a single token, so it's start and end location both point at the beginning of the token"\(hello)". However, the expressionhellohas a source range consisting of the single tokenhello. Notice thathellocomes after"\(hello)" in the source file, despite being logically contained within the source range of"(hello)"`.Since ASTScope lookup relies on SourceRanges of parent nodes containing the SourceRanges of their parents, adding a child scope would sometimes have to "widen" the parent's source range. This was error-prone and complex.
Instead, we can use CharSourceRanges. Since the end location of a CharSourceRange is a byte offset of the end of the last token of the CharSourceRange, we the required invariant around nested scopes for free, without having to "widen" source ranges.
This PR adds stronger assertions for detecting children which are not contained in their parents, or overlapping sibling children.
Builds upon #34205, which fixes all the non-string-interpolation cases where source range "widening" was required.
Fixes https://bugs.swift.org/browse/SR-12997, https://bugs.swift.org/browse/SR-12999, rdar://problem/64314753, rdar://problem/64316115.