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Fix FormatString false positive for switch expression arguments #5967

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Fix FormatString false positive for switch expression arguments #5967

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8f35ddf
Fix FormatString false positive for switch expression arguments
arimu1 Jul 27, 2026
2c64580
fix(formatstring): recurse switch case typing for nested/yield forms
arimu1 Jul 27, 2026
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62 changes: 61 additions & 1 deletion .../src/main/java/com/google/errorprone/bugpatterns/formatstring/FormatStringValidation.java
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Original file line number Diff line number Diff line change
Expand Up @@ -26,9 +26,14 @@
import com.google.errorprone.VisitorState;
import com.google.errorprone.suppliers.Supplier;
import com.google.errorprone.util.ASTHelpers;
import com.sun.source.tree.BlockTree;
import com.sun.source.tree.CaseTree;
import com.sun.source.tree.ConditionalExpressionTree;
import com.sun.source.tree.ExpressionTree;
import com.sun.source.tree.StatementTree;
import com.sun.source.tree.SwitchExpressionTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.YieldTree;
import com.sun.source.util.SimpleTreeVisitor;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import com.sun.tools.javac.code.Type;
Expand Down Expand Up @@ -150,14 +155,69 @@ protected Void defaultAction(Tree tree, Void unused) {
* or {@link Integer}.
*/
private static @Nullable Object getInstance(Tree tree, VisitorState state) {
tree = ASTHelpers.stripParentheses(tree);
Object value = ASTHelpers.constValue(tree);
if (value != null) {
return value;
}
Type type = ASTHelpers.getType(tree);
Type type = getExpressionType(tree, state);
return getInstance(type, state);
}

private static @Nullable Type getExpressionType(Tree tree, VisitorState state) {
tree = ASTHelpers.stripParentheses(tree);
if (tree instanceof SwitchExpressionTree switchExpression) {
Type fromCases = switchExpressionResultType(switchExpression, state);
if (fromCases != null && fromCases.getKind() != TypeKind.ERROR) {
return fromCases;
}
}
return ASTHelpers.getType(tree);
}

private static @Nullable Type switchExpressionResultType(
SwitchExpressionTree switchExpression, VisitorState state) {
Types types = state.getTypes();
Type common = null;
for (CaseTree caseTree : switchExpression.getCases()) {
Type caseType = getSwitchCaseResultType(caseTree, state);
if (caseType == null || caseType.getKind() == TypeKind.ERROR) {
continue;
}
Type normalized = types.unboxedTypeOrType(types.erasure(caseType));
if (common == null) {
common = normalized;
} else if (!types.isSameType(common, normalized)) {
return null;
}
}
return common;
}

private static @Nullable Type getSwitchCaseResultType(CaseTree caseTree, VisitorState state) {
Tree body = caseTree.getBody();
if (body == null) {
for (StatementTree statement : caseTree.getStatements()) {
if (statement instanceof YieldTree yieldTree) {
return getExpressionType(yieldTree.getValue(), state);
}
}
return null;
}
body = ASTHelpers.stripParentheses(body);
if (body instanceof ExpressionTree expressionTree) {
return getExpressionType(expressionTree, state);
}
if (body instanceof BlockTree blockTree) {
for (StatementTree statement : blockTree.getStatements()) {
if (statement instanceof YieldTree yieldTree) {
return getExpressionType(yieldTree.getValue(), state);
}
}
}
return getExpressionType(body, state);
}

private static @Nullable Object getInstance(Type type, VisitorState state) {
Types types = state.getTypes();
if (type.getKind() == TypeKind.NULL) {
Expand Down
111 changes: 111 additions & 0 deletions core/src/test/java/com/google/errorprone/bugpatterns/formatstring/FormatStringTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -466,4 +466,115 @@ public static void main() {
""")
.doTest();
}

@Test
public void switchExpressionArgument() {
compilationHelper
.addSourceLines(
"Test.java",
"""
class Test {
static final int FRIDAY = 5;

void f() {
int day = FRIDAY;
var viaVar = switch (day) {
case 1, 5, 7 -> 6;
case 2 -> 7;
default -> 9;
};
System.out.printf("via var: %d%n", viaVar);
System.out.printf(
"inline: %d%n",
switch (day) {
case 1, 5, 7 -> 6;
case 2 -> 7;
default -> 9;
});
}
}
""")
.doTest();
}

@Test
public void switchExpressionArgument_nestedSwitch() {
compilationHelper
.addSourceLines(
"Test.java",
"""
class Test {
void f(int day, int mode) {
System.out.printf(
"%d%n",
switch (day) {
case 1 -> switch (mode) {
case 0 -> 1;
default -> 2;
};
default -> 3;
});
}
}
""")
.doTest();
}

@Test
public void switchExpressionArgument_blockYield() {
compilationHelper
.addSourceLines(
"Test.java",
"""
class Test {
void f(int day) {
System.out.printf(
"%d%n",
switch (day) {
case 1 -> {
yield 6;
}
default -> 9;
});
}
}
""")
.doTest();
}

@Test
public void switchExpressionArgument_colonYield() {
compilationHelper
.addSourceLines(
"Test.java",
"""
class Test {
void f(int day) {
System.out.printf(
"%d%n",
switch (day) {
case 1:
yield 6;
default:
yield 9;
});
}
}
""")
.doTest();
}

@Test
public void switchExpressionArgument_stringCases() {
testFormat(
"illegal format conversion: 'java.lang.String' cannot be formatted using '%d'",
"System.out.printf(\"%d\", switch (1) { case 1 -> \"a\"; default -> \"b\"; });");
}

@Test
public void switchExpressionArgument_mixedNumericCases() {
testFormat(
"cannot be formatted using '%d'",
"System.out.printf(\"%d\", switch (1) { case 1 -> 1; default -> 2.0; });");
}
}