Revert "[clang][analyzer] Change default value of checker option in u…

…nix.StdCLibraryFunctions. (#80457)"

This reverts commit 7af4e8b.

clang/docs/analyzer/checkers.rst

@@ -1320,23 +1320,10 @@ range of the argument.
 
 **Parameters**
 
-The ``ModelPOSIX`` option controls if functions from the POSIX standard are
-recognized by the checker.
-
-With ``ModelPOSIX=true``, many POSIX functions are modeled according to the
-`POSIX standard`_. This includes ranges of parameters and possible return
-values. Furthermore the behavior related to ``errno`` in the POSIX case is
-often that ``errno`` is set only if a function call fails, and it becomes
-undefined after a successful function call.
-
-With ``ModelPOSIX=false``, this checker follows the C99 language standard and
-only models the functions that are described there. It is possible that the
-same functions are modeled differently in the two cases because differences in
-the standards. The C standard specifies less aspects of the functions, for
-example exact ``errno`` behavior is often unspecified (and not modeled by the
-checker).
-
-Default value of the option is ``true``.
+The checker models functions (and emits diagnostics) from the C standard by
+default. The ``ModelPOSIX`` option enables modeling (and emit diagnostics) of
+additional functions that are defined in the POSIX standard. This option is
+disabled by default.
 
 .. _osx-checkers:
 

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

@@ -578,7 +578,7 @@ def StdCLibraryFunctionsChecker : Checker<"StdCLibraryFunctions">,
                   "ModelPOSIX",
                   "If set to true, the checker models additional functions "
                   "from the POSIX standard.",
-                  "true",
+                  "false",
                   InAlpha>
   ]>,
   WeakDependencies<[CallAndMessageChecker, NonNullParamChecker]>,

clang/test/Analysis/analyzer-config.c

@@ -129,7 +129,7 @@
 // CHECK-NEXT: unix.DynamicMemoryModeling:Optimistic = false
 // CHECK-NEXT: unix.Errno:AllowErrnoReadOutsideConditionExpressions = true
 // CHECK-NEXT: unix.StdCLibraryFunctions:DisplayLoadedSummaries = false
-// CHECK-NEXT: unix.StdCLibraryFunctions:ModelPOSIX = true
+// CHECK-NEXT: unix.StdCLibraryFunctions:ModelPOSIX = false
 // CHECK-NEXT: unroll-loops = false
 // CHECK-NEXT: verbose-report-filename = false
 // CHECK-NEXT: widen-loops = false