[clang][analyzer] Improve documentation of checker 'cplusplus.Move' (NFC) (#96295)

Author: balazske

clang/docs/analyzer/checkers.rst

@@ -420,21 +420,56 @@ around, such as ``std::string_view``.
 
 cplusplus.Move (C++)
 """"""""""""""""""""
-Method calls on a moved-from object and copying a moved-from object will be reported.
-
+Find use-after-move bugs in C++. This includes method calls on moved-from
+objects, assignment of a moved-from object, and repeated move of a moved-from
+object.
 
 .. code-block:: cpp
 
-  struct A {
+ struct A {
    void foo() {}
  };
 
- void f() {
+ void f1() {
    A a;
    A b = std::move(a); // note: 'a' became 'moved-from' here
    a.foo();            // warn: method call on a 'moved-from' object 'a'
  }
 
+ void f2() {
+   A a;
+   A b = std::move(a);
+   A c(std::move(a)); // warn: move of an already moved-from object
+ }
+
+ void f3() {
+   A a;
+   A b = std::move(a);
+   b = a; // warn: copy of moved-from object
+ }
+
+The checker option ``WarnOn`` controls on what objects the use-after-move is
+checked:
+
+* The most strict value is ``KnownsOnly``, in this mode only objects are
+  checked whose type is known to be move-unsafe. These include most STL objects
+  (but excluding move-safe ones) and smart pointers.
+* With option value ``KnownsAndLocals`` local variables (of any type) are
+  additionally checked. The idea behind this is that local variables are
+  usually not tempting to be re-used so an use after move is more likely a bug
+  than with member variables.
+* With option value ``All`` any use-after move condition is checked on all
+  kinds of variables, excluding global variables and known move-safe cases.
+
+Default value is ``KnownsAndLocals``.
+
+Calls of methods named ``empty()`` or ``isEmpty()`` are allowed on moved-from
+objects because these methods are considered as move-safe. Functions called
+``reset()``, ``destroy()``, ``clear()``, ``assign``, ``resize``,  ``shrink`` are
+treated as state-reset functions and are allowed on moved-from objects, these
+make the object valid again. This applies to any type of object (not only STL
+ones).
+
 .. _cplusplus-NewDelete:
 
 cplusplus.NewDelete (C++)

clang/include/clang/StaticAnalyzer/Checkers/Checkers.td

@@ -686,22 +686,11 @@ def MoveChecker: Checker<"Move">,
   CheckerOptions<[
     CmdLineOption<String,
                   "WarnOn",
-                  "In non-aggressive mode, only warn on use-after-move of "
-                  "local variables (or local rvalue references) and of STL "
-                  "objects. The former is possible because local variables (or "
-                  "local rvalue references) are not tempting their user to "
-                  "re-use the storage. The latter is possible because STL "
-                  "objects are known to end up in a valid but unspecified "
-                  "state after the move and their state-reset methods are also "
-                  "known, which allows us to predict precisely when "
-                  "use-after-move is invalid. Some STL objects are known to "
-                  "conform to additional contracts after move, so they are not "
-                  "tracked. However, smart pointers specifically are tracked "
-                  "because we can perform extra checking over them. In "
-                  "aggressive mode, warn on any use-after-move because the "
-                  "user has intentionally asked us to completely eliminate "
-                  "use-after-move in his code. Values: \"KnownsOnly\", "
-                  "\"KnownsAndLocals\", \"All\".",
+                  "With setting \"KnownsOnly\" warn only on objects with known "
+                  "move semantics like smart pointers and other STL objects. "
+                  "With setting \"KnownsAndLocals\" warn additionally on local "
+                  "variables (or rvalue references). With setting \"All\" warn "
+                  "on all variables (excluding global variables).",
                   "KnownsAndLocals",
                   Released>
   ]>,

clang/test/Analysis/analyzer-checker-option-help.c

@@ -34,27 +34,7 @@
 // CHECK-STABLE: OPTIONS:
 //
 // CHECK-STABLE:   cplusplus.Move:WarnOn
-// CHECK-STABLE-SAME:          (string) In non-aggressive mode, only warn
-// CHECK-STABLLE:              on use-after-move of local variables (or
-// CHECK-STABLLE:              local rvalue references) and of STL objects.
-// CHECK-STABLLE:              The former is possible because local variables
-// CHECK-STABLLE:              (or local rvalue references) are not tempting
-// CHECK-STABLLE:              their user to re-use the storage. The latter
-// CHECK-STABLLE:              is possible because STL objects are known
-// CHECK-STABLLE:              to end up in a valid but unspecified state
-// CHECK-STABLLE:              after the move and their state-reset methods
-// CHECK-STABLLE:              are also known, which allows us to predict
-// CHECK-STABLLE:              precisely when use-after-move is invalid.
-// CHECK-STABLLE:              Some STL objects are known to conform to
-// CHECK-STABLLE:              additional contracts after move, so they
-// CHECK-STABLLE:              are not tracked. However, smart pointers
-// CHECK-STABLLE:              specifically are tracked because we can
-// CHECK-STABLLE:              perform extra checking over them. In aggressive
-// CHECK-STABLLE:              mode, warn on any use-after-move because
-// CHECK-STABLLE:              the user has intentionally asked us to completely
-// CHECK-STABLLE:              eliminate use-after-move in his code. Values:
-// CHECK-STABLLE:              "KnownsOnly", "KnownsAndLocals", "All".
-// CHECK-STABLLE:              (default: KnownsAndLocals)
+// CHECK-STABLE-SAME:         (string) With setting "KnownsOnly" warn
 
 // CHECK-STABLE-NOT: debug.AnalysisOrder:*
 // CHECK-DEVELOPER:  debug.AnalysisOrder:*