[analyzer] Update undefined assignment diagnostics to not use 'garbage'

A clang user pointed out that messages for the static analyzer undefined
assignment checker use the term 'garbage'.  This is kind of snarky and
also imprecise. This change replaces the term 'garbage' in those messages
with 'not meaningful'. It moves the term 'undefined' to be first in the
messages because of the possible ambiguous parsing of the term 'not
 meaningful and undefined'. That could be parsed as '(not meaningful)
and undefined' or 'not (meaningful and undefined').

The use of the term 'meaningless' was considered, but not chosen because
it has two meanings in English. One meaning is 'without meaning'. The
other meaning is 'having no point'. The 2nd meaning could be construed
as indicating the computation could be deleted.

rdar://133418644

Author: dtarditi

clang/lib/StaticAnalyzer/Checkers/UndefinedAssignmentChecker.cpp

@@ -23,7 +23,7 @@ using namespace ento;
 namespace {
 class UndefinedAssignmentChecker
   : public Checker<check::Bind> {
-  const BugType BT{this, "Assigned value is garbage or undefined"};
+  const BugType BT{this, "Assigned value is undefined and not meaningful"};
 
 public:
   void checkBind(SVal location, SVal val, const Stmt *S,
@@ -57,8 +57,8 @@ void UndefinedAssignmentChecker::checkBind(SVal location, SVal val,
 
   while (StoreE) {
     if (const UnaryOperator *U = dyn_cast<UnaryOperator>(StoreE)) {
-      OS << "The expression is an uninitialized value. "
-            "The computed value will also be garbage";
+      OS << "The expression is an uninitialized value, so the computed value "
+         << "is not meaningful";
 
       ex = U->getSubExpr();
       break;
@@ -68,7 +68,7 @@ void UndefinedAssignmentChecker::checkBind(SVal location, SVal val,
       if (B->isCompoundAssignmentOp()) {
         if (C.getSVal(B->getLHS()).isUndef()) {
           OS << "The left expression of the compound assignment is an "
-                "uninitialized value. The computed value will also be garbage";
+             << "uninitialized value, so the computed value is not meaningful";
           ex = B->getLHS();
           break;
         }
@@ -88,8 +88,9 @@ void UndefinedAssignmentChecker::checkBind(SVal location, SVal val,
       if (CD->isImplicit()) {
         for (auto *I : CD->inits()) {
           if (I->getInit()->IgnoreImpCasts() == StoreE) {
-            OS << "Value assigned to field '" << I->getMember()->getName()
-               << "' in implicit constructor is garbage or undefined";
+            OS << "Value assigned to field '"
+               << I->getMember()->getName()
+               << "' in implicit constructor is undefined and not meaningful.";
             break;
           }
         }

clang/test/Analysis/Inputs/expected-plists/edges-new.mm.plist

@@ -2578,17 +2578,17 @@
      </array>
      <key>depth</key><integer>0</integer>
      <key>extended_message</key>
-     <string>The left expression of the compound assignment is an uninitialized value. The computed value will also be garbage</string>
+     <string>The left expression of the compound assignment is an uninitialized value, so the computed value is not meaningful</string>
      <key>message</key>
-     <string>The left expression of the compound assignment is an uninitialized value. The computed value will also be garbage</string>
+     <string>The left expression of the compound assignment is an uninitialized value, so the computed value is not meaningful</string>
     </dict>
    </array>
-   <key>description</key><string>The left expression of the compound assignment is an uninitialized value. The computed value will also be garbage</string>
+   <key>description</key><string>The left expression of the compound assignment is an uninitialized value, so the computed value is not meaningful</string>
    <key>category</key><string>Logic error</string>
-   <key>type</key><string>Assigned value is garbage or undefined</string>
+   <key>type</key><string>Assigned value is undefined and not meaningful</string>
    <key>check_name</key><string>core.uninitialized.Assign</string>
    <!-- This hash is experimental and going to change! -->
-   <key>issue_hash_content_of_line_in_context</key><string>025372576cd3ba6716044f93a51c978c</string>
+   <key>issue_hash_content_of_line_in_context</key><string>936a5fabf36091d0c1e1e1553232d6f5</string>
   <key>issue_context_kind</key><string>function</string>
   <key>issue_context</key><string>test_objc_fast_enumeration_2</string>
   <key>issue_hash_function_offset</key><string>5</string>

clang/test/Analysis/Inputs/expected-plists/plist-output.m.plist

@@ -5864,17 +5864,17 @@
      </array>
      <key>depth</key><integer>0</integer>
      <key>extended_message</key>
-     <string>The left expression of the compound assignment is an uninitialized value. The computed value will also be garbage</string>
+     <string>The left expression of the compound assignment is an uninitialized value, so the computed value is not meaningful</string>
      <key>message</key>
-     <string>The left expression of the compound assignment is an uninitialized value. The computed value will also be garbage</string>
+     <string>The left expression of the compound assignment is an uninitialized value, so the computed value is not meaningful</string>
     </dict>
    </array>
-   <key>description</key><string>The left expression of the compound assignment is an uninitialized value. The computed value will also be garbage</string>
+   <key>description</key><string>The left expression of the compound assignment is an uninitialized value, so the computed value is not meaningful</string>
    <key>category</key><string>Logic error</string>
-   <key>type</key><string>Assigned value is garbage or undefined</string>
+   <key>type</key><string>Assigned value is undefined and not meaningful</string>
    <key>check_name</key><string>core.uninitialized.Assign</string>
    <!-- This hash is experimental and going to change! -->
-   <key>issue_hash_content_of_line_in_context</key><string>21c774309bdfd487c3d09a61a671bbcc</string>
+   <key>issue_hash_content_of_line_in_context</key><string>c1d7b1284317d7e45bda4bfa6b3a281e</string>
   <key>issue_context_kind</key><string>function</string>
   <key>issue_context</key><string>test_loop_fast_enumeration</string>
   <key>issue_hash_function_offset</key><string>5</string>

clang/test/Analysis/a_flaky_crash.cpp

@@ -14,7 +14,7 @@ bool bar(S);
 void foo() {
   int x;
   if (true && bar(S()))
-    ++x; // expected-warning{{The expression is an uninitialized value. The computed value will also be garbage}}
+    ++x; // expected-warning{{The expression is an uninitialized value, so the computed value is not meaningful}}
 }
 
 // 256 copies of the same run-line to make it crash more often when it breaks.

clang/test/Analysis/analysis-after-multiple-dtors.cpp

@@ -23,6 +23,6 @@ int main() {
 
   int x;
   int y = x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
   (void)y;
 }

clang/test/Analysis/array-init-loop.cpp

@@ -19,7 +19,7 @@ void array_uninit() {
 
   auto [a, b, c, d, e] = arr;
 
-  int x = e; // expected-warning{{Assigned value is garbage or undefined}}
+  int x = e; // expected-warning{{Assigned value is undefined and not meaningful}}
 }
 
 void lambda_init() {
@@ -168,7 +168,7 @@ struct S3_duplicate {
 void array_uninit_non_pod() {
   S3 arr[1];
 
-  auto [a] = arr; // expected-warning@159{{ in implicit constructor is garbage or undefined }}
+  auto [a] = arr; // expected-warning@159{{ in implicit constructor is undefined and not meaningful}}
 }
 
 void lambda_init_non_pod() {
@@ -191,7 +191,7 @@ void lambda_init_non_pod() {
 void lambda_uninit_non_pod() {
   S3_duplicate arr[4];
 
-  int l = [arr] { return arr[3].i; }(); // expected-warning@164{{ in implicit constructor is garbage or undefined }}
+  int l = [arr] { return arr[3].i; }(); // expected-warning@164{{ in implicit constructor is undefined and not meaningful }}
 }
 
 // If this struct is being copy/move constructed by the implicit ctors, ArrayInitLoopExpr

clang/test/Analysis/array-punned-region.c

@@ -20,7 +20,7 @@ void array_struct_bitfield_1() {
 int array_struct_bitfield_2() {
   BITFIELD_CAST ff = {0};
   BITFIELD_CAST *pff = &ff;
-  int a = *((int *)pff + 2); // expected-warning{{Assigned value is garbage or undefined [core.uninitialized.Assign]}}
+  int a = *((int *)pff + 2); // expected-warning{{Assigned value is undefined and not meaningful [core.uninitialized.Assign]}}
   return a;
 }
 

clang/test/Analysis/builtin_overflow_notes.c

@@ -23,8 +23,8 @@ void test_overflow_note(int a, int b)
 
    if (__builtin_add_overflow(a, b, &res)) { // expected-note {{Assuming overflow}}
                                              // expected-note@-1 {{Taking true branch}}
-     int var = res; // expected-warning{{Assigned value is garbage or undefined}}
-                    // expected-note@-1 {{Assigned value is garbage or undefined}}
+     int var = res; // expected-warning{{Assigned value is undefined and not meaningful}}
+                    // expected-note@-1 {{Assigned value is undefined and not meaningful}}
      return;
    }
 }

clang/test/Analysis/call-invalidation.cpp

@@ -197,7 +197,7 @@ int testStdCtorDoesNotInvalidateParentObject() {
 int testStdCtorDoesNotInvalidateParentObjectSwapped() {
   StdWrappingOpaqueSwapped obj;
   int x = obj.o.nested_member; // no-garbage: std::Opaque::ctor might initialized this
-  int y = obj.uninit; // expected-warning {{Assigned value is garbage or undefined}}
+  int y = obj.uninit; // expected-warning {{Assigned value is undefined and not meaningful}}
   return x + y;
 }
 
@@ -277,6 +277,6 @@ struct StdWrappingFancyOpaque {
 int testNestedStdNamespacesAndRecords() {
   StdWrappingFancyOpaque obj;
   int x = obj.o.nested_member; // no-garbage: ctor
-  int y = obj.uninit; // expected-warning {{Assigned value is garbage or undefined}}
+  int y = obj.uninit; // expected-warning {{Assigned value is undefined and not meaningful}}
   return x + y;
 }

clang/test/Analysis/ctor-array.cpp

@@ -12,19 +12,19 @@ struct s {
 void a1(void) {
   s arr[3];
   int x = arr[0].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 void a2(void) {
   s arr[3];
   int x = arr[1].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 void a3(void) {
   s arr[3];
   int x = arr[2].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 struct s2 {
@@ -37,23 +37,23 @@ void b1(void) {
 
   clang_analyzer_eval(arr[0].y == 2); // expected-warning{{TRUE}}
   int x = arr[0].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 void b2(void) {
   s2 arr[3];
 
   clang_analyzer_eval(arr[1].y == 2); // expected-warning{{TRUE}}
   int x = arr[1].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 void b3(void) {
   s2 arr[3];
 
   clang_analyzer_eval(arr[2].y == 2); // expected-warning{{TRUE}}
   int x = arr[2].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 void c1(void) {
@@ -70,7 +70,7 @@ void c1(void) {
 
     clang_analyzer_eval(arr[1].y == 2); // expected-warning{{TRUE}}
     int x = arr[1].x;
-    // expected-warning@-1{{Assigned value is garbage or undefined}}
+    // expected-warning@-1{{Assigned value is undefined and not meaningful}}
   }
 }
 
@@ -100,15 +100,15 @@ void e1(void) {
   clang_analyzer_eval(arr[1].arr[1].y == 2); // expected-warning{{TRUE}}
 
   int x = arr[1].sarr[1].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 void f1(void) {
   s2 arr[2][2];
 
   clang_analyzer_eval(arr[1][1].y == 2); // expected-warning{{TRUE}}
   int x = arr[1][1].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 struct s5 {
@@ -168,14 +168,14 @@ void h2(void) {
   s a[2][2], b[2][2];
 
   int x = a[1][1].x;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 void h3(void) {
   s a[2][2], b[2][2];
 
   int x = b[1][1].y;
-  // expected-warning@-1{{Assigned value is garbage or undefined}}
+  // expected-warning@-1{{Assigned value is undefined and not meaningful}}
 }
 
 struct Base {