[Parse] Handle #if in brace skipping logic

Previously we would strictly match `{` + `}`, but
that ignored the fact that when parsing we consider
`#if` + `#endif` to be a stronger delimiter than
`{` + `}`, so can ignore a stray `}` in a `#if`.
Update the logic to also track opening and closing
`#if` decls, ignoring any braces that happen within
them.

rdar://129195380

lib/Parse/ParseDecl.cpp

@@ -5658,10 +5658,11 @@ static unsigned skipUntilMatchingRBrace(Parser &P,
   HasPotentialRegexLiteral = false;
 
   unsigned OpenBraces = 1;
+  unsigned OpenPoundIf = 0;
 
   bool LastTokenWasFunc = false;
 
-  while (OpenBraces != 0 && P.Tok.isNot(tok::eof)) {
+  while ((OpenBraces != 0 || OpenPoundIf != 0) && P.Tok.isNot(tok::eof)) {
     // Detect 'func' followed by an operator identifier.
     if (LastTokenWasFunc) {
       LastTokenWasFunc = false;
@@ -5692,6 +5693,24 @@ static unsigned skipUntilMatchingRBrace(Parser &P,
       return OpenBraces;
     }
 
+    // Match opening `#if` with closing `#endif` to match what the parser does,
+    // `#if` + `#endif` are considered stronger delimiters than `{` + `}`.
+    if (P.consumeIf(tok::pound_if)) {
+      OpenPoundIf += 1;
+      continue;
+    }
+    if (OpenPoundIf != 0) {
+      // We're in a `#if`, check to see if we've reached the end.
+      if (P.consumeIf(tok::pound_endif)) {
+        OpenPoundIf -= 1;
+        continue;
+      }
+      // Consume the next token and continue iterating. We can swallow any
+      // amount of '{' and '}' while in the `#if`.
+      P.consumeToken();
+      continue;
+    }
+
     if (P.consumeIf(tok::l_brace)) {
       ++OpenBraces;
       continue;

test/Parse/rdar129195380.swift

@@ -0,0 +1,36 @@
+// RUN: not %target-swift-frontend -experimental-skip-all-function-bodies -dump-parse %s | %FileCheck %s
+
+// rdar://129195380 - Make sure the skipping logic can handle #if.
+struct S {
+  // CHECK: func_decl{{.*}}:[[@LINE+1]]:3 - line:[[@LINE+11]]:3{{.*}}"foo()"
+  func foo() {
+#if true
+  }
+#if true
+  func bar() {
+#else
+  }
+#endif
+  }
+#endif
+  }
+  // CHECK: func_decl{{.*}}:[[@LINE+1]]:3 - line:[[@LINE+1]]:15{{.*}}"baz()"
+  func baz() {}
+}
+
+// The '#if' is unterminated here, so swallows the rest of the file.
+// CHECK: struct_decl{{.*}}:[[@LINE+1]]:1 - line:[[@LINE+14]]:14{{.*}}"R"
+struct R {
+#if false
+  }
+#if true
+  }
+#endif
+  }
+#else
+  }
+  // CHECK-NOT: qux
+  func qux() {}
+}
+
+func flim() {}

test/SourceKit/CursorInfo/rdar129195380.swift

@@ -0,0 +1,13 @@
+// rdar://129195380 - Make sure we correctly handle '#if' when skipping function
+// bodies.
+class C {
+  func test1() {
+  #if FOOBAR
+// RUN: %sourcekitd-test -req=cursor -pos=%(line + 2):5 %s -- %s -DFOOBAR
+// RUN: %sourcekitd-test -req=cursor -pos=%(line + 1):5 %s -- %s
+    abc
+  }
+
+  func test2() {
+  }
+}