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[StatementSwitchToExpressionSwitch] add support for patterns and guards in old-style (colon) switches. #5352

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Merged
merged 1 commit into from
Nov 18, 2025
+172 −15
Merged

[StatementSwitchToExpressionSwitch] add support for patterns and guards in old-style (colon) switches. #5352

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42 changes: 27 additions & 15 deletions core/src/main/java/com/google/errorprone/bugpatterns/StatementSwitchToExpressionSwitch.java
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Original file line number Diff line number Diff line change
Expand Up @@ -64,6 +64,7 @@
import com.sun.source.tree.IdentifierTree;
import com.sun.source.tree.LabeledStatementTree;
import com.sun.source.tree.MemberSelectTree;
import com.sun.source.tree.PatternCaseLabelTree;
import com.sun.source.tree.ReturnTree;
import com.sun.source.tree.StatementTree;
import com.sun.source.tree.SwitchTree;
Expand Down Expand Up @@ -299,15 +300,6 @@ private static AnalysisResult analyzeSwitchTree(SwitchTree switchTree, VisitorSt
// One-pass scan through each case in switch
for (int caseIndex = 0; caseIndex < cases.size(); caseIndex++) {
CaseTree caseTree = cases.get(caseIndex);
boolean hasCasePattern =
caseTree.getLabels().stream()
.anyMatch(
caseLabelTree -> caseLabelTree.getKind().name().equals("PATTERN_CASE_LABEL"));
if (hasCasePattern) {
// Case patterns are not currently supported by the checker.
return DEFAULT_ANALYSIS_RESULT;
}

NullDefaultKind nullDefaultKind = analyzeCaseForNullAndDefault(caseTree);
boolean isDefaultCase =
nullDefaultKind.equals(NullDefaultKind.KIND_DEFAULT)
Expand Down Expand Up @@ -1014,7 +1006,7 @@ private static SuggestedFix convertDirectlyToExpressionSwitch(
}

if (nullDefaultKind.equals(NullDefaultKind.KIND_NEITHER)) {
replacementCodeBuilder.append(printCaseExpressions(caseTree, state));
replacementCodeBuilder.append(printCaseExpressionsOrPatternAndGuard(caseTree, state));
}
Optional<String> commentsAfterCaseOptional =
extractCommentsAfterCase(switchTree, allSwitchComments, state, caseIndex);
Expand Down Expand Up @@ -1159,7 +1151,7 @@ private static SuggestedFix convertToReturnSwitch(
}

if (nullDefaultKind.equals(NullDefaultKind.KIND_NEITHER)) {
replacementCodeBuilder.append(printCaseExpressions(caseTree, state));
replacementCodeBuilder.append(printCaseExpressionsOrPatternAndGuard(caseTree, state));
}

Optional<String> commentsAfterCaseOptional =
Expand Down Expand Up @@ -1395,7 +1387,7 @@ private static SuggestedFix convertToAssignmentSwitch(
}

if (nullDefaultKind.equals(NullDefaultKind.KIND_NEITHER)) {
replacementCodeBuilder.append(printCaseExpressions(caseTree, state));
replacementCodeBuilder.append(printCaseExpressionsOrPatternAndGuard(caseTree, state));
}

Optional<String> commentsAfterCaseOptional =
Expand Down Expand Up @@ -1722,9 +1714,29 @@ private static String removeFallThruLines(String comments) {
}
}

/** Prints source for all expressions in a given {@code case}, separated by commas. */
private static String printCaseExpressions(CaseTree caseTree, VisitorState state) {
return caseTree.getExpressions().stream().map(state::getSourceForNode).collect(joining(", "));
private static boolean hasCasePattern(CaseTree caseTree) {
return caseTree.getLabels().stream()
.anyMatch(caseLabelTree -> caseLabelTree instanceof PatternCaseLabelTree);
}

/**
* Prints source for all expressions in a given {@code case}, separated by commas, or the pattern
* and guard (if present).
*/
private static String printCaseExpressionsOrPatternAndGuard(
CaseTree caseTree, VisitorState state) {
if (!hasCasePattern(caseTree)) {
return caseTree.getExpressions().stream().map(state::getSourceForNode).collect(joining(", "));
}
// Currently, `case`s can only have a single pattern, however the compiler's class structure
// does not reflect this restriction.
StringBuilder sb =
new StringBuilder(
caseTree.getLabels().stream().map(state::getSourceForNode).collect(joining(", ")));
if (caseTree.getGuard() != null) {
sb.append(" when ").append(state.getSourceForNode(caseTree.getGuard())).append(" ");
}
return sb.toString();
}

/**
Expand Down
145 changes: 145 additions & 0 deletions ...rc/test/java/com/google/errorprone/bugpatterns/StatementSwitchToExpressionSwitchTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1205,6 +1205,52 @@ public static void main(String[] args) {
.doTest(TEXT_MATCH);
}

@Test
public void switchOnString_patterns_error() {
refactoringHelper
.addInputLines(
"Test.java",
"""
public class Test {
public static void main(String[] args) {
switch (args[0]) {
case String s
when s.startsWith("a sale"):
{
System.out.println("it all starts with a sale");
break;
}
case "one":
System.out.println("one");
break;
case "two", "three":
System.out.println("two or three");
break;
case String s:
System.out.println("some other string");
break;
}
}
}
""")
.addOutputLines(
"Test.java",
"""
public class Test {
public static void main(String[] args) {
switch (args[0]) {
case String s when s.startsWith("a sale") -> System.out.println("it all starts with a sale");
case "one" -> System.out.println("one");
case "two", "three" -> System.out.println("two or three");
case String s -> System.out.println("some other string");
}
}
}
""")
.setArgs("-XepOpt:StatementSwitchToExpressionSwitch:EnableDirectConversion=true")
.doTest(TEXT_MATCH);
}

@Test
public void unnecessaryBreaks() {
refactoringHelper
Expand Down Expand Up @@ -1343,6 +1389,105 @@ public int foo(Suit suit) {
.doTest();
}

@Test
public void switchByEnum_casePatternAndGuard_error() {

refactoringHelper
.addInputLines(
"Test.java",
"""
class Test {
public int foo(Suit suit) {
switch (suit) {
case HEART:
case DIAMOND:
return 1;
case SPADE:
System.out.println("spade");
throw new RuntimeException();
case CLUB:
throw new NullPointerException();
case Suit s
when s == Suit.HEART:
throw new NullPointerException();
default:
throw new NullPointerException();
}
}
}
""")
.addOutputLines(
"Test.java",
"""
class Test {
public int foo(Suit suit) {
return switch (suit) {
case HEART, DIAMOND -> 1;
case SPADE -> {
System.out.println("spade");
throw new RuntimeException();
}
case CLUB -> throw new NullPointerException();
case Suit s when s == Suit.HEART -> throw new NullPointerException();
default -> throw new NullPointerException();
};
}
}
""")
.setArgs(
"-XepOpt:StatementSwitchToExpressionSwitch:EnableReturnSwitchConversion",
"-XepOpt:StatementSwitchToExpressionSwitch:EnableDirectConversion=false")
.setFixChooser(FixChoosers.FIRST)
.doTest();

refactoringHelper2
.addInputLines(
"Test.java",
"""
class Test {
public int foo(Suit suit) {
switch (suit) {
case HEART:
case DIAMOND:
return 1;
case SPADE:
System.out.println("spade");
throw new RuntimeException();
case CLUB:
throw new NullPointerException();
case Suit s
when s == Suit.HEART:
throw new NullPointerException();
default:
throw new NullPointerException();
}
}
}
""")
.addOutputLines(
"Test.java",
"""
class Test {
public int foo(Suit suit) {
return switch (suit) {
case HEART, DIAMOND -> 1;
case SPADE -> {
System.out.println("spade");
throw new RuntimeException();
}
case CLUB -> throw new NullPointerException();
case Suit s when s == Suit.HEART -> throw new NullPointerException();
};
}
}
""")
.setArgs(
"-XepOpt:StatementSwitchToExpressionSwitch:EnableReturnSwitchConversion",
"-XepOpt:StatementSwitchToExpressionSwitch:EnableDirectConversion=false")
.setFixChooser(FixChoosers.SECOND)
.doTest();
}

@Test
public void switchByEnum_middleNullCase_noError() {
// The HEART case cannot be grouped with the null case per Java syntax
Expand Down
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