[InlinableText] Handle multiline #if conditions (#19675)

Previously, a #if of the form:

```swift
#if (
  false
)
print("x")
#endif
```

Would be emitted after #if-stripping as

```swift
  false
)
print("x")
```

Because the old logic assumed conditions will always appear on one line.
Instead, for active clauses that have conditions, skip to the next line
after the end of the condition instead.

Author: Harlan

lib/AST/InlinableText.cpp

@@ -14,6 +14,7 @@
 #include "swift/AST/ASTWalker.h"
 #include "swift/AST/ASTNode.h"
 #include "swift/AST/Decl.h"
+#include "swift/AST/Expr.h"
 #include "swift/Parse/Lexer.h"
 
 #include "llvm/ADT/SmallVector.h"
@@ -92,9 +93,15 @@ struct ExtractInactiveRanges : public ASTWalker {
       return false;
     }
 
-    // Ignore range from beginning of '#if' to the beginning of the elements
-    // of this clause.
-    addRange(start, Lexer::getLocForEndOfLine(sourceMgr, clause->Loc));
+    // Ignore range from beginning of '#if', '#elseif', or '#else' to the
+    // beginning of the elements of this clause.
+    auto elementsBegin = clause->Loc;
+    // If there's a condition (e.g. this isn't a '#else' block), then ignore
+    // everything up to the end of the condition.
+    if (auto cond = clause->Cond) {
+      elementsBegin = cond->getEndLoc();
+    }
+    addRange(start, Lexer::getLocForEndOfLine(sourceMgr, elementsBegin));
 
     // Ignore range from effective end of the elements of this clause to the
     // end of the '#endif'

test/ModuleInterface/if-configs.swift

@@ -69,6 +69,37 @@ public func hasClosureDefaultArgWithComplexPoundIf(_ x: () -> Void = {
 }) {
 }
 
+// CHECK: func hasClosureDefaultArgWithMultilinePoundIfCondition(_ x: () -> Void = {
+// CHECK-NOT: #if (
+// CHECK-NOT:   !false && true
+// CHECK-NOT: )
+// CHECK: print("should appear")
+// CHECK-NOT: #endif
+// CHECK-NOT: #if (
+// CHECK-NOT:   !true
+// CHECK-NOT: )
+// CHECK-NOT: print("should not appear")
+// CHECK-NOT: #else
+// CHECK: print("also should appear")
+// CHECK-NOT: #endif
+// CHECK-NEXT: })
+public func hasClosureDefaultArgWithMultilinePoundIfCondition(_ x: () -> Void = {
+  #if (
+    !false && true
+  )
+  print("should appear")
+  #endif
+
+  #if (
+    !true
+  )
+  print("should not appear")
+  #else
+  print("also should appear")
+  #endif
+}) {
+}
+
 // CHECK: func hasClosureDefaultArgWithSinglePoundIf(_ x: () -> Void = {
 // CHECK-NOT: #if true
 // CHECK: print("true")
@@ -85,7 +116,6 @@ public func hasClosureDefaultArgWithSinglePoundIf(_ x: () -> Void = {
 }) {
 }
 
-
 // CHECK: func hasSimpleDefaultArgs(_ x: Int = 0, b: Int = 1)
 public func hasSimpleDefaultArgs(_ x: Int = 0, b: Int = 1) {
 }