[analyzer] scan-build: Fix silencing multiple core checkers.

[NoQ]

Summary

It was only silencing one checker because -analyzer-config flags can only carry one value at a time.

The silencing mechanism is still not working correctly in presence of conflicting flags, i.e. scan-build -disable-checker core.foo -enable-checker core.foo leaves core.foo silenced whereas scan-build -disable-checker unix.foo -enable-checker unix.foo leaves unix.foo enabled. I'd prefer to promote silencing to a frontend flag in order to fix that but that'd be more work that's fairly orthogonal and i'm currently looking for a quick fix.

[Charusso]

I do not get why my solution -analyzer-config silence-checkers=core.NullDereference -analyzer-config silence-checkers=core.DivideZero was insufficient, whereas -analyzer-config silence-checkers=core.NullDereference;core.DivideZero is working. One funny thing to note here: LLDB cannot parse "a;b", so that it stops to parse the compiler flags at ;... It is mostly LLDB's fault, but that is why I wanted to avoid the character ;. If I remember right I have picked ; over ,, because the Clang's flag-parser cannot parse ,, but may , is working now. Could you try that and overwrite these silly behaviors, please?

This scan-build testing script is super repetitive to use, but it is great we could test these in place. Cool stuff!

[Szelethus]

In D84084#2160089, @Charusso wrote:

I do not get why my solution -analyzer-config silence-checkers=core.NullDereference -analyzer-config silence-checkers=core.DivideZero was insufficient, whereas -analyzer-config silence-checkers=core.NullDereference;core.DivideZero is working.

Because analyzer configs only hold the last value to be friendly towards scripts (just like most other configs/flags in clang).

If I remember right I have picked ; over ,, because the Clang's flag-parser cannot parse ,, but may , is working now.

The problem is that it fishes for multiple analyzer configs: -analyzer-config option1=value1 -analyzer-config option2=value2 == -analyzer-config option1=value1,option2=value2.

I'd prefer to promote silencing to a frontend flag in order to fix that but that'd be more work that's fairly orthogonal and i'm currently looking for a quick fix.

I think the functionality to silence warnings should be there, not the actual flag. Ideally, disabling a checker should achieve what silencing is currently doing now.

[NoQ]

In D84084#2160252, @Szelethus wrote:

In D84084#2160089, @Charusso wrote:

I do not get why my solution -analyzer-config silence-checkers=core.NullDereference -analyzer-config silence-checkers=core.DivideZero was insufficient, whereas -analyzer-config silence-checkers=core.NullDereference;core.DivideZero is working.

Because analyzer configs only hold the last value to be friendly towards scripts (just like most other configs/flags in clang).

Yup, that's because AnalyzerOptions is a map. It cannot (and was never expected to) hold more than one value per key.

Even if there was a list data type in -analyzer-config that would have been appended rather than replaced upon getting specified multiple times, in our case such list would still need to interact with other frontend flags in a non-trivial way (i.e., the result has to be different depending on how it's placed in the command with respect to -analyzer-checker).

In D84084#2160252, @Szelethus wrote:

I think the functionality to silence warnings should be there, not the actual flag. Ideally, disabling a checker should achieve what silencing is currently doing now.

Hmm, yeah, that might actually be a better option.

[NoQ]

Forgot the phabricator link T_T
Committed in rG0b2a9222463.

clang/test/Analysis/scan-build/Inputs/null_dereference_and_division_by_zero.c

+
+int test(int x) {
+  if (x) {
+    int *p = 0;
+    return *p; // Null dereference.
+  } else {
+    return 1 / x; // Division by zero.
+  }
+}

clang/test/Analysis/scan-build/silence-core-checkers.test

+// FIXME: Actually, "perl".
+REQUIRES: shell
+
+RUN: rm -rf %t.output_dir && mkdir %t.output_dir
+RUN: %scan-build -o %t.output_dir \
+RUN:   %clang -S %S/Inputs/null_dereference_and_division_by_zero.c \
+RUN:   | FileCheck %s -check-prefix CHECK-TWO-BUGS
+
+RUN: rm -rf %t.output_dir && mkdir %t.output_dir
+RUN: %scan-build -o %t.output_dir \
+RUN:   -disable-checker core.DivideZero \
+RUN:   %clang -S %S/Inputs/null_dereference_and_division_by_zero.c \
+RUN:   | FileCheck %s -check-prefix CHECK-ONE-BUG
+
+RUN: rm -rf %t.output_dir && mkdir %t.output_dir
+RUN: %scan-build -o %t.output_dir \
+RUN:   -disable-checker core.NullDereference \
+RUN:   %clang -S %S/Inputs/null_dereference_and_division_by_zero.c \
+RUN:   | FileCheck %s -check-prefix CHECK-ONE-BUG
+
+RUN: rm -rf %t.output_dir && mkdir %t.output_dir
+RUN: %scan-build -o %t.output_dir \
+RUN:   -disable-checker core.NullDereference \
+RUN:   -disable-checker core.DivideZero \
+RUN:   %clang -S %S/Inputs/null_dereference_and_division_by_zero.c \
+RUN:   | FileCheck %s -check-prefix CHECK-NO-BUGS
+
+CHECK-NO-BUGS: scan-build: No bugs found.
+CHECK-ONE-BUG: scan-build: 1 bug found.
+CHECK-TWO-BUGS: scan-build: 2 bugs found.

clang/tools/scan-build/bin/scan-build

 if ($Options{MaxLoop} > 0) { push @AnalysesToRun, "-analyzer-max-loop $Options{MaxLoop}"; }
 
 # Delay setting up other environment variables in case we can do true
 # interposition.
 my $CCC_ANALYZER_ANALYSIS = join ' ', @AnalysesToRun;
 my $CCC_ANALYZER_PLUGINS = join ' ', map { "-load ".$_ } @{$Options{PluginsToLoad}};
 my $CCC_ANALYZER_CONFIG = join ' ', map { "-analyzer-config ".$_ } @{$Options{ConfigOptions}};
 
-foreach (sort { $Options{SilenceCheckers}{$a} <=> $Options{SilenceCheckers}{$b} }
-         keys %{$Options{SilenceCheckers}}) {
-  # Add checkers in order they were silenced.
+if (%{$Options{SilenceCheckers}}) {
   $CCC_ANALYZER_CONFIG =
-      $CCC_ANALYZER_CONFIG." -analyzer-config silence-checkers=".$_;
+      $CCC_ANALYZER_CONFIG." -analyzer-config silence-checkers="
+                          .join(';', sort {
+                                            $Options{SilenceCheckers}{$a} <=>
+                                            $Options{SilenceCheckers}{$b}
+                                          } keys %{$Options{SilenceCheckers}});
 }
 
 my %EnvVars = (
   'CC' => $Cmd,
   'CXX' => $CmdCXX,
   'CLANG' => $Clang,
   'CLANG_CXX' => $ClangCXX,
   'VERBOSE' => $Options{Verbose},