Add source buffers pretty-printed for diagnostics to serialized diagnostics

When emitting a diagnostic that references a declaration that does not
itself have a source location (e.g., because it was synthesized or
deserialized), the diagnostics engine pretty-prints the declaration
into a buffer so it can provide caret diagnostics pointing to that
declaration.

Start marking those buffers as "generated source buffers", so that we
emit their contents into serialized diagnostics files. This will allow
tools that make use of serialized diagnostics to also show caret
information.

Author: DougGregor

include/swift/Basic/SourceManager.h

@@ -36,6 +36,9 @@ class GeneratedSourceInfo {
 
     /// A new function body that is replacing an existing function body.
     ReplacedFunctionBody,
+
+    /// Pretty-printed declarations that have no source location.
+    PrettyPrinted,
   } kind;
 
   /// The buffer ID for the enclosing buffer, in which originalSourceRange

lib/AST/DiagnosticEngine.cpp

@@ -1142,6 +1142,7 @@ DiagnosticEngine::diagnosticInfoForDiagnostic(const Diagnostic &diagnostic) {
         SmallVector<std::pair<const Decl *, uint64_t>, 8> entries;
         llvm::SmallString<128> buffer;
         llvm::SmallString<128> bufferName;
+        const Decl *ppDecl = decl;
         {
           // The access level of the buffer we want to print. Declarations below
           // this access level will be omitted from the buffer; declarations
@@ -1152,7 +1153,6 @@ DiagnosticEngine::diagnosticInfoForDiagnostic(const Diagnostic &diagnostic) {
 
           // Figure out which declaration to print. It's the top-most
           // declaration (not a module).
-          const Decl *ppDecl = decl;
           auto dc = decl->getDeclContext();
 
           // FIXME: Horrible, horrible hackaround. We're not getting a
@@ -1237,6 +1237,21 @@ DiagnosticEngine::diagnosticInfoForDiagnostic(const Diagnostic &diagnostic) {
         auto bufferID = SourceMgr.addMemBufferCopy(buffer, bufferName);
         auto memBufferStartLoc = SourceMgr.getLocForBufferStart(bufferID);
 
+        SourceMgr.setGeneratedSourceInfo(
+            bufferID,
+            GeneratedSourceInfo{
+              GeneratedSourceInfo::PrettyPrinted,
+              bufferID,
+              SourceRange(),
+              SourceRange(
+                  memBufferStartLoc,
+                  memBufferStartLoc.getAdvancedLoc(buffer.size())
+              ),
+              ASTNode(const_cast<Decl *>(ppDecl)).getOpaqueValue(),
+              nullptr
+            }
+        );
+
         // Go through all of the pretty-printed entries and record their
         // locations.
         for (auto entry : entries) {
@@ -1318,12 +1333,18 @@ std::vector<Diagnostic> DiagnosticEngine::getGeneratedSourceBufferNotes(
       break;
     }
 
+    case GeneratedSourceInfo::PrettyPrinted:
+      break;
+
     case GeneratedSourceInfo::ReplacedFunctionBody:
       return childNotes;
     }
 
     // Walk up the stack.
     currentLoc = expansionNode.getStartLoc();
+    if (currentLoc.isInvalid())
+      return childNotes;
+
     currentBufferID = SourceMgr.findBufferContainingLoc(currentLoc);
   } while (true);
 }

lib/Basic/SourceLoc.cpp

@@ -260,6 +260,7 @@ void SourceManager::setGeneratedSourceInfo(
 
   switch (info.kind) {
   case GeneratedSourceInfo::MacroExpansion:
+  case GeneratedSourceInfo::PrettyPrinted:
     break;
 
   case GeneratedSourceInfo::ReplacedFunctionBody:

test/ImportResolution/import-specific-fixits.swift

@@ -55,6 +55,9 @@ import struct ambiguous.funcOrVar // expected-error{{ambiguous name 'funcOrVar'
 // CHECK-NEXT: Number FIXITs = 0
 // CHECK-NEXT: note: found this candidate
 // CHECK-NEXT: Number FIXITs = 0
+// CHECK-NEXT: CONTENTS OF FILE ambiguous_right.funcOrVar:
+// CHECK: public var funcOrVar: Int
+// CHECK: END CONTENTS OF FILE
 // CHECK-NEXT: note: found this candidate
 
 import func ambiguous.someVar // expected-error{{ambiguous name 'someVar' in module 'ambiguous'}}

test/Misc/serialized-diagnostics-prettyprint.swift

@@ -0,0 +1,14 @@
+// RUN: rm -f %t.*
+
+// Test swift executable
+// RUN: %target-swift-frontend -typecheck -serialize-diagnostics-path %t.dia %s -verify
+// RUN: c-index-test -read-diagnostics %t.dia > %t.deserialized_diagnostics.txt 2>&1
+// RUN: %FileCheck --input-file=%t.deserialized_diagnostics.txt %s
+
+var x = String.init // expected-error{{ambiguous use of 'init'}}
+// CHECK: {{.*[/\\]}}serialized-diagnostics-prettyprint.swift:[[@LINE-1]]:9: error: ambiguous use of 'init'
+
+// CHECK: Swift.String:2:23: note: found this candidate
+// CHECK: CONTENTS OF FILE Swift.String:
+// CHECK: extension String {
+// CHECK:    public init(_ content: Substring.UnicodeScalarView)