[AST] Give appendInterpolation refs a SourceLoc

This change permits UnresolvedDotExpr to have both a name and a base that are implicit, but a valid DotLoc, and to treat that DotLoc as the node’s location. It then changes the generation of string interpolation code so that `$stringInterpolation.appendInterpolation` references have a DotLoc corresponding to the backslash in the string literal.

This makes it possible for `ExprContextAnalyzer` in IDE to correctly detect when you are code-completing in a string interpolation and treat it as an `appendInterpolation` call.

Author: beccadax

include/swift/AST/Expr.h

@@ -2377,14 +2377,30 @@ class UnresolvedDotExpr : public Expr {
                                                  : FunctionRefKind::Unapplied);
   }
 
-  SourceLoc getLoc() const { return NameLoc.getBaseNameLoc(); }
+  SourceLoc getLoc() const {
+    if (NameLoc.isValid())
+      return NameLoc.getBaseNameLoc();
+    else if (DotLoc.isValid())
+      return DotLoc;
+    else
+      return SubExpr->getEndLoc();
+  }
 
   SourceLoc getStartLoc() const {
-    return (DotLoc.isInvalid() ? NameLoc.getSourceRange().End 
-                               : SubExpr->getStartLoc());
+    if (SubExpr->getStartLoc().isValid())
+      return SubExpr->getStartLoc();
+    else if (DotLoc.isValid())
+      return DotLoc;
+    else
+      return NameLoc.getSourceRange().Start;
   }
   SourceLoc getEndLoc() const {
-    return NameLoc.getSourceRange().End;
+    if (NameLoc.isValid())
+      return NameLoc.getSourceRange().End;
+    else if (DotLoc.isValid())
+      return DotLoc;
+    else
+      return SubExpr->getEndLoc();
   }
 
   SourceLoc getDotLoc() const { return DotLoc; }

lib/Parse/ParseExpr.cpp

@@ -1863,8 +1863,8 @@ parseStringSegments(SmallVectorImpl<Lexer::StringSegment> &Segments,
                                        SyntaxKind::ExpressionSegment);
 
       // Backslash is part of an expression segment.
-      Token BackSlash(tok::backslash,
-                      CharSourceRange(Segment.Loc.getAdvancedLoc(-1), 1).str());
+      SourceLoc BackSlashLoc = Segment.Loc.getAdvancedLoc(-1);
+      Token BackSlash(tok::backslash, CharSourceRange(BackSlashLoc, 1).str());
       ExprContext.addToken(BackSlash, EmptyTrivia, EmptyTrivia);
       // Create a temporary lexer that lexes from the body of the string.
       LexerState BeginState =
@@ -1889,7 +1889,7 @@ parseStringSegments(SmallVectorImpl<Lexer::StringSegment> &Segments,
                                            tok::string_interpolation_anchor);
 
       auto callee = new (Context) UnresolvedDotExpr(InterpolationVarRef,
-                                                    /*dotloc=*/SourceLoc(),
+                                                    /*dotloc=*/BackSlashLoc,
                                                     appendInterpolation,
                                                     /*nameloc=*/DeclNameLoc(),
                                                     /*Implicit=*/true);

test/IDE/complete_at_top_level.swift

@@ -470,10 +470,9 @@ func resyncParserB14() {}
 var stringInterp = "\(#^STRING_INTERP_3^#)"
 _ = "" + "\(#^STRING_INTERP_4^#)" + ""
 // STRING_INTERP: Begin completions
-// FIXME: Why is this TypeRelation[Invalid] in STRING_INTERP_4?
-// STRING_INTERP-DAG: Decl[InstanceMethod]/CurrNominal{{(/NotRecommended/TypeRelation\[Invalid\])?}}:   ['(']{#(value): _#}[')'][#Void#]; name=value: _
+// STRING_INTERP-DAG: Decl[InstanceMethod]/CurrNominal:   ['(']{#(value): _#}[')'][#Void#]; name=value: _
 // STRING_INTERP-DAG: Decl[Struct]/CurrModule: FooStruct[#FooStruct#];
-// STRING_INTERP-DAG: Decl[FreeFunction]/CurrModule: fooFunc1()[#Void#];
+// STRING_INTERP-DAG: Decl[FreeFunction]/CurrModule/NotRecommended/TypeRelation[Invalid]: fooFunc1()[#Void#];
 // STRING_INTERP-DAG: Decl[FreeFunction]/CurrModule: optStr()[#String?#];
 // STRING_INTERP-DAG: Decl[GlobalVar]/Local: fooObject[#FooStruct#];
 // STRING_INTERP: End completions