Suppress warnings for non-primary inputs

Don't emit warnings if specified at the command line or when working
on a non-primary input file.

https://bugs.swift.org/browse/SR-1012
rdar://problem/25282622

Author: bitjammer

lib/Frontend/Frontend.cpp

@@ -430,6 +430,10 @@ void CompilerInstance::performSema() {
     if (BufferID == PrimaryBufferID)
       setPrimarySourceFile(NextInput);
 
+    auto &Diags = NextInput->getASTContext().Diags;
+    auto DidSuppressWarnings = Diags.getSuppressWarnings();
+    Diags.setSuppressWarnings(DidSuppressWarnings || BufferID != PrimaryBufferID);
+
     bool Done;
     do {
       // Parser may stop at some erroneous constructions like #else, #endif
@@ -438,6 +442,8 @@ void CompilerInstance::performSema() {
                           &PersistentState, DelayedCB.get());
     } while (!Done);
 
+    Diags.setSuppressWarnings(DidSuppressWarnings);
+
     performNameBinding(*NextInput);
   }
 
@@ -471,6 +477,11 @@ void CompilerInstance::performSema() {
 
     SourceFile &MainFile =
       MainModule->getMainSourceFile(Invocation.getSourceFileKind());
+
+    auto &Diags = MainFile.getASTContext().Diags;
+    auto DidSuppressWarnings = Diags.getSuppressWarnings();
+    Diags.setSuppressWarnings(DidSuppressWarnings || !mainIsPrimary);
+
     SILParserState SILContext(TheSILModule.get());
     unsigned CurTUElem = 0;
     bool Done;
@@ -488,6 +499,8 @@ void CompilerInstance::performSema() {
       }
       CurTUElem = MainFile.Decls.size();
     } while (!Done);
+
+    Diags.setSuppressWarnings(DidSuppressWarnings);
 
     if (mainIsPrimary && !Context->hadError() &&
         Invocation.getFrontendOptions().PlaygroundTransform)

test/Parse/Inputs/warning_nonprimary_file.swift

@@ -0,0 +1,6 @@
+#if os(asdf)
+public func bar(x: Int, _ y: Int) -> Int {
+  return x + y
+}
+#endif
+

test/Parse/warning_primary_file.swift

@@ -0,0 +1,20 @@
+// RUN: %target-swift-frontend -parse -verify -primary-file %s %S/Inputs/warning_nonprimary_file.swift
+
+// Tests that parse warnings are only emitted for the primary
+// input. Below, we expect a warning diagnostic to be emitted
+// because this is the primary file.
+//
+// However, we also pull in ./warning_nonprimary_file.swift,
+// which would emit a warning for an unknown operating system
+// configuration argument, but doesn't because it's not the
+// primary input.
+
+public func foo(x: Int, y: Int) -> Int {
+  return x + y
+}
+
+public func baz(x: Int, y: Int) -> Int {
+  var z = x // expected-warning {{variable 'z' was never mutated}}
+  return z + y
+}
+