Reduce minimum number of affected pointers for -warn-root-cause to 1 (#721)

Root causes will now be emitted if they affect at least one pointer.
This is a change from the previous minimum of two affected pointers.
Fixes #685.

Author: john-h-kastner

clang/lib/3C/RewriteUtils.cpp

@@ -589,11 +589,10 @@ void RewriteConsumer::emitRootCauseDiagnostics(ASTContext &Context) {
       if (!File.getError()) {
         SourceLocation SL =
             SM.translateFileLineCol(*File, PSL.getLineNo(), PSL.getColSNo());
-        // Limit emitted root causes to those that effect more than one pointer
-        // or are in the main file of the TU. Alternatively, don't filter causes
-        // if -warn-all-root-cause is passed.
+        // Limit emitted root causes to those that effect at least one pointer.
+        // Alternatively, don't filter causes if -warn-all-root-cause is passed.
         int PtrCount = I.getNumPtrsAffected(WReason.first);
-        if (_3COpts.WarnAllRootCause || SM.isInMainFile(SL) || PtrCount > 1) {
+        if (_3COpts.WarnAllRootCause || PtrCount > 0) {
           // SL is invalid when the File is not in the current translation unit.
           if (SL.isValid()) {
             EmittedDiagnostics.insert(PSL);

clang/test/3C/base_subdir/unwritable_rootcauses.c

@@ -1,4 +1,6 @@
 // RUN: cd %S
 // RUN: 3c -use-malloc=my_malloc -alltypes -addcr -output-dir=%t.checked/base_subdir -warn-all-root-cause %s -- -Xclang -verify=unwritable-expected -Wno-everything
+// RUN: 3c -use-malloc=my_malloc -alltypes -addcr -output-dir=%t.checked/base_subdir -warn-root-cause %s -- -Xclang -verify=not-all-unwritable-expected -Wno-everything
+// not-all-unwritable-expected-no-diagnostics
 
 #include "../root_cause.c"

clang/test/3C/root_cause.c

@@ -1,4 +1,5 @@
 // RUN: 3c -use-malloc=my_malloc -base-dir=%S -alltypes -warn-all-root-cause %s -- -Xclang -verify -Wno-everything
+// RUN: 3c -use-malloc=my_malloc -base-dir=%S -alltypes -warn-root-cause %s -- -Xclang -verify -Wno-everything
 
 // This test is unusual in that it checks for the errors in the code
 
@@ -106,5 +107,4 @@ void test_conflict() {
 // expected-note@#as_ptr {{Operand of address-of has PTR lower bound}}
 // expected-note@#as_nt {{Assigning from c to s}}
 
-
-
+#include "root_cause.h"

clang/test/3C/root_cause.h

@@ -0,0 +1,9 @@
+// Test that root cause errors are reported correctly in include header files.
+// Included by root_cause.c
+
+void outside_of_main() {
+  // expected-warning@+3 {{1 unchecked pointer: Cast from int to int *}}
+  // unwritable-expected-warning@+2 {{0 unchecked pointers: Source code in non-writable file}}
+  // unwritable-expected-warning@+1 {{0 unchecked pointers: Source code in non-writable file}}
+  int *c = 1;
+}