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148 lines
5.9 KiB
ReStructuredText
148 lines
5.9 KiB
ReStructuredText
.. _advanced_check_features:
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Advanced Check Features
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=======================
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This page covers additional ways to improve and extend the check you've added to build/clang-plugin.
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Adding Tests
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------------
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No doubt you've seen the tests for existing checks in `build/clang-plugin/tests <https://searchfox.org/mozilla-central/source/build/clang-plugin/tests>`_. Adding tests is straightforward; and your reviewer should insist you do so. Simply copying the existing format of any test and how diagnostics are marked as expected.
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One wrinkle - all clang plugin checks are applied to all tests. We try to write tests so that only one check applies to it. If you write a check that triggers on an existing test, try to fix the existing test slightly so the new check does not trigger on it.
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Using Bind To Output More Useful Information
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--------------------------------------------
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You've probably been wondering what the heck ``.bind()`` is for. You've been seeing it all over the place but never has it actually been explained what it's for and when to use it.
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``.bind()`` is used to give a name to part of the AST discovered through your matcher, so you can use it later. Let's go back to our sample matcher:
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::
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AstMatcher->addMatcher(
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traverse(TK_IgnoreUnlessSpelledInSource,
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ifStmt(allOf(
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has(
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binaryOperator(
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has(
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declRefExpr(hasType(enumDecl()))
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)
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)
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),
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hasElse(
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ifStmt(allOf(
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unless(hasElse(anything())),
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has(
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binaryOperator(
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has(
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declRefExpr(hasType(enumDecl()))
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)
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)
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)
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))
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)
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))
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.bind("node")),
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this);
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Now the ``.bind("node")`` makes more sense. We're naming the If statement we matched, so we can refer to it later when we call ``Result.Nodes.getNodeAs<IfStmt>("node")``.
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Let's say we want to provide the *type* of the enum in our warning message. There are two enums we end up seeing in our matcher - the enum in the first if statement, and the enum in the second. We're going to arbitrarily pick the first and give it the name ``enumType``:
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::
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AstMatcher->addMatcher(
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traverse(TK_IgnoreUnlessSpelledInSource,
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ifStmt(allOf(
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has(
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binaryOperator(
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has(
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declRefExpr(hasType(enumDecl().bind("enumType")))
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)
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)
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),
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hasElse(
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ifStmt(allOf(
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unless(hasElse(anything())),
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has(
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binaryOperator(
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has(
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declRefExpr(hasType(enumDecl()))
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)
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)
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)
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))
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)
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))
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.bind("node")),
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this);
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And in our check() function, we can use it like so:
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::
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void MissingElseInEnumComparisons::check(
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const MatchFinder::MatchResult &Result) {
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const auto *MatchedDecl = Result.Nodes.getNodeAs<IfStmt>("node");
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const auto *EnumType = Result.Nodes.getNodeAs<EnumDecl>("enumType");
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diag(MatchedDecl->getIfLoc(),
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"Enum comparisons to %0 in an if/else if block without a trailing else.",
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DiagnosticIDs::Warning) << EnumType->getName();
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}
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Repeated matcher calls
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--------------------------
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If you find yourself repeating the same several matchers in several spots, you can turn it into a variable to use.
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::
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auto isTemporaryLifetimeBoundCall =
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cxxMemberCallExpr(
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onImplicitObjectArgument(anyOf(has(cxxTemporaryObjectExpr()),
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has(materializeTemporaryExpr()))),
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callee(functionDecl(isMozTemporaryLifetimeBound())));
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auto hasTemporaryLifetimeBoundCall =
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anyOf(isTemporaryLifetimeBoundCall,
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conditionalOperator(
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anyOf(hasFalseExpression(isTemporaryLifetimeBoundCall),
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hasTrueExpression(isTemporaryLifetimeBoundCall))));
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The above example is parameter-less, but if you need to supply a parameter that changes, you can turn it into a lambda:
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::
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auto hasConstCharPtrParam = [](const unsigned int Position) {
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return hasParameter(
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Position, hasType(hasCanonicalType(pointsTo(asString("const char")))));
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};
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auto hasParamOfType = [](const unsigned int Position, const char *Name) {
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return hasParameter(Position, hasType(asString(Name)));
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};
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auto hasIntegerParam = [](const unsigned int Position) {
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return hasParameter(Position, hasType(isInteger()));
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};
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AstMatcher->addMatcher(
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callExpr(
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hasName("fopen"),
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hasConstCharPtrParam(0))
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.bind("funcCall"),
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this);
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Allow-listing existing callsites
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--------------------------------
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While it's not a great situation, you can set up an allow-list of existing callsites if you need to. A simple allow-list is demonstrated in `NoGetPrincipalURI <https://hg.mozilla.org/mozilla-central/rev/fb60b22ee6616521b386d90aec07b03b77905f4e>`_. The `NoNewThreadsChecker <https://hg.mozilla.org/mozilla-central/rev/f400f164b3947b4dd54089a36ea31cca2d72805b>`_ is an example of a more sophisticated way of setting up a larger allow-list.
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Custom Annotations
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------------------
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It's possible to create custom annotations that will be a no-op when compiled, but can be used by a static analysis check. These can be used to annotate special types of sources and sinks (for example). We have some examples of this in-tree presently (such as ``MOZ_CAN_RUN_SCRIPT``) but currently don't have a detailed walkthrough in this documentation of how to set these up and use them. (Patches welcome.)
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