clang-format-20 issue with breaking after cast

[rjarry]

Given the following configuration:

.clang-format

---
AccessModifierOffset: -4
AlignAfterOpenBracket: BlockIndent
AlignArrayOfStructures: None
AlignConsecutiveAssignments: None
AlignConsecutiveBitFields: None
AlignConsecutiveDeclarations: None
AlignConsecutiveMacros: None
AlignEscapedNewlines: Right
AlignOperands: DontAlign
AlignTrailingComments: false
AllowAllArgumentsOnNextLine: true
AllowAllParametersOfDeclarationOnNextLine: false
AllowShortBlocksOnASingleLine: Empty
AllowShortCaseLabelsOnASingleLine: false
AllowShortEnumsOnASingleLine: false
AllowShortFunctionsOnASingleLine: Empty
AllowShortIfStatementsOnASingleLine: Never
AllowShortLambdasOnASingleLine: None
AllowShortLoopsOnASingleLine: false
AlwaysBreakAfterDefinitionReturnType: None
AlwaysBreakAfterReturnType: None
AlwaysBreakBeforeMultilineStrings: false
AlwaysBreakTemplateDeclarations: MultiLine
AttributeMacros:
  - __capability
BinPackArguments: false
BinPackParameters: false
BitFieldColonSpacing: Both
BraceWrapping:
  AfterCaseLabel: false
  AfterClass: false
  AfterControlStatement: Never
  AfterEnum: false
  AfterExternBlock: false
  AfterFunction: false
  AfterNamespace: false
  AfterObjCDeclaration: false
  AfterStruct: false
  AfterUnion: false
  BeforeCatch: false
  BeforeElse: false
  BeforeLambdaBody: false
  BeforeWhile: false
  IndentBraces: false
  SplitEmptyFunction: true
  SplitEmptyNamespace: true
  SplitEmptyRecord: true
BreakBeforeBinaryOperators: All
BreakBeforeBraces: Custom
BreakBeforeConceptDeclarations: false
BreakBeforeTernaryOperators: false
BreakConstructorInitializers: BeforeComma
BreakConstructorInitializersBeforeComma: false
BreakInheritanceList: BeforeColon
BreakStringLiterals: true
ColumnLimit: 100
CommentPragmas: '^ IWYU pragma:'
CompactNamespaces: false
ConstructorInitializerAllOnOneLineOrOnePerLine: false
ConstructorInitializerIndentWidth: 8
ContinuationIndentWidth: 8
Cpp11BracedListStyle: true
DeriveLineEnding: true
DerivePointerAlignment: false
DisableFormat: false
EmptyLineAfterAccessModifier: Never
EmptyLineBeforeAccessModifier: LogicalBlock
ExperimentalAutoDetectBinPacking: false
FixNamespaceComments: false
ForEachMacros:
  - LIST_FOREACH
  - LIST_FOREACH_SAFE
  - RTE_ETH_FOREACH_DEV
  - RTE_LCORE_FOREACH
  - SLIST_FOREACH
  - SLIST_FOREACH_SAFE
  - STAILQ_FOREACH
  - STAILQ_FOREACH_SAFE
  - TAILQ_FOREACH
  - TAILQ_FOREACH_SAFE
  - rte_graph_foreach_node
  - gr_vec_foreach
  - gr_vec_foreach_ref
  - gr_nh_flags_foreach
IfMacros:
  - KJ_IF_MAYBE
IncludeBlocks: Regroup
IncludeCategories:
  - Regex:           '^".*'
    Priority:        -1
  - Regex:           '^<(gr_|gr\.)'
    Priority:        100
  - Regex:           '^<(rte_|event|ecoli|numa.h|libsmartcols.h)'
    Priority:        500
  - Regex:           '^<cmocka'
    Priority:        100000
  - Regex:           '^<'
    Priority:        10000
IncludeIsMainRegex: '(Test)?$'
IncludeIsMainSourceRegex: ''
IndentAccessModifiers: false
IndentCaseBlocks: false
IndentCaseLabels: false
IndentExternBlock: AfterExternBlock
IndentGotoLabels: false
IndentPPDirectives: None
IndentRequires: false
IndentWidth: 8
IndentWrappedFunctionNames: false
InsertTrailingCommas: Wrapped
KeepEmptyLinesAtTheStartOfBlocks: false
LambdaBodyIndentation: Signature
MacroBlockBegin: ''
MacroBlockEnd:   ''
MaxEmptyLinesToKeep: 1
NamespaceIndentation: Inner
ObjCBinPackProtocolList: Auto
ObjCBlockIndentWidth: 4
ObjCBreakBeforeNestedBlockParam: true
ObjCSpaceAfterProperty: true
ObjCSpaceBeforeProtocolList: true
PPIndentWidth: -1
PackConstructorInitializers: BinPack
PenaltyBreakAssignment: 100000000
PenaltyBreakBeforeFirstCallParameter: 0
PenaltyBreakComment: 20
PenaltyBreakFirstLessLess: 120
PenaltyBreakOpenParenthesis: 400
PenaltyBreakString: 100
PenaltyBreakTemplateDeclaration: 10
PenaltyExcessCharacter: 100000
PenaltyIndentedWhitespace: 1000
PenaltyReturnTypeOnItsOwnLine: 100
PointerAlignment: Right
QualifierAlignment: Leave
ReferenceAlignment: Pointer
ReflowComments: false
RemoveBracesLLVM: false
SeparateDefinitionBlocks: Leave
ShortNamespaceLines: 1
SortIncludes: CaseSensitive
SortUsingDeclarations: true
SpaceAfterCStyleCast: false
SpaceAfterLogicalNot: false
SpaceAfterTemplateKeyword: true
SpaceAroundPointerQualifiers: Default
SpaceBeforeAssignmentOperators: true
SpaceBeforeCaseColon: false
SpaceBeforeCpp11BracedList: true
SpaceBeforeCtorInitializerColon: true
SpaceBeforeInheritanceColon: true
SpaceBeforeParens: ControlStatements
SpaceBeforeParensOptions:
  AfterControlStatements: true
  AfterForeachMacros: true
  AfterFunctionDeclarationName: false
  AfterFunctionDefinitionName: false
  AfterIfMacros: true
  BeforeNonEmptyParentheses: false
SpaceBeforeRangeBasedForLoopColon: true
SpaceBeforeSquareBrackets: false
SpaceInEmptyBlock: true
SpaceInEmptyParentheses: false
SpacesBeforeTrailingComments: 1
SpacesInAngles: Never
SpacesInCStyleCastParentheses: false
SpacesInConditionalStatement: false
SpacesInContainerLiterals: true
SpacesInLineCommentPrefix:
  Minimum: 1
  Maximum: -1
SpacesInParentheses: false
SpacesInSquareBrackets: false
Standard: c++20
StatementAttributeLikeMacros:
  - Q_EMIT
StatementMacros:
  - Q_UNUSED
  - QT_REQUIRE_VERSION
TabWidth: 8
UseCRLF: false
UseTab: Always
WhitespaceSensitiveMacros:
  - BOOST_PP_STRINGIZE
  - CF_SWIFT_NAME
  - NS_SWIFT_NAME
  - PP_STRINGIZE
  - STRINGIZE
...

And this example file (formatted with clang-format 19):

#include <stddef.h>
#include <stdint.h>

#define ICMP6_ERR_DEST_UNREACH 2

struct rte_mbuf;
struct icmp6_err_dest_unreach {
	int foo;
};

char *rte_pktmbuf_prepend(struct rte_mbuf *m, uint16_t len);

void test(struct rte_mbuf *mbuf, int icmp_type);

void test(struct rte_mbuf *mbuf, int icmp_type) {
	struct icmp6_err_dest_unreach *du;
	if (mbuf != NULL) {
		switch (icmp_type) {
                case ICMP6_ERR_DEST_UNREACH:
			du = (struct icmp6_err_dest_unreach *)
				rte_pktmbuf_prepend(mbuf, sizeof(*du));
                        break;
		}
	}
}

When formatting it with clang-format 20 (same configuration), I get a different result:

--- clang-format-19.c
+++ clang-format-20.c
@@ -17,8 +17,8 @@ void test(struct rte_mbuf *mbuf, int icm
        if (mbuf != NULL) {
                switch (icmp_type) {
                case ICMP6_ERR_DEST_UNREACH:
-                       du = (struct icmp6_err_dest_unreach *)
-                               rte_pktmbuf_prepend(mbuf, sizeof(*du));
+                       du = (struct icmp6_err_dest_unreach *
+                       )rte_pktmbuf_prepend(mbuf, sizeof(*du));
                        break;
                }
        }

Maybe I missed a new option but, this looks like a bug/regression.

[llvmbot]

@llvm/issue-subscribers-clang-format

Author: Robin Jarry (rjarry)

Given the following configuration:

<details>
<summary>.clang-format</summary>

---
AccessModifierOffset: -4
AlignAfterOpenBracket: BlockIndent
AlignArrayOfStructures: None
AlignConsecutiveAssignments: None
AlignConsecutiveBitFields: None
AlignConsecutiveDeclarations: None
AlignConsecutiveMacros: None
AlignEscapedNewlines: Right
AlignOperands: DontAlign
AlignTrailingComments: false
AllowAllArgumentsOnNextLine: true
AllowAllParametersOfDeclarationOnNextLine: false
AllowShortBlocksOnASingleLine: Empty
AllowShortCaseLabelsOnASingleLine: false
AllowShortEnumsOnASingleLine: false
AllowShortFunctionsOnASingleLine: Empty
AllowShortIfStatementsOnASingleLine: Never
AllowShortLambdasOnASingleLine: None
AllowShortLoopsOnASingleLine: false
AlwaysBreakAfterDefinitionReturnType: None
AlwaysBreakAfterReturnType: None
AlwaysBreakBeforeMultilineStrings: false
AlwaysBreakTemplateDeclarations: MultiLine
AttributeMacros:
  - __capability
BinPackArguments: false
BinPackParameters: false
BitFieldColonSpacing: Both
BraceWrapping:
  AfterCaseLabel: false
  AfterClass: false
  AfterControlStatement: Never
  AfterEnum: false
  AfterExternBlock: false
  AfterFunction: false
  AfterNamespace: false
  AfterObjCDeclaration: false
  AfterStruct: false
  AfterUnion: false
  BeforeCatch: false
  BeforeElse: false
  BeforeLambdaBody: false
  BeforeWhile: false
  IndentBraces: false
  SplitEmptyFunction: true
  SplitEmptyNamespace: true
  SplitEmptyRecord: true
BreakBeforeBinaryOperators: All
BreakBeforeBraces: Custom
BreakBeforeConceptDeclarations: false
BreakBeforeTernaryOperators: false
BreakConstructorInitializers: BeforeComma
BreakConstructorInitializersBeforeComma: false
BreakInheritanceList: BeforeColon
BreakStringLiterals: true
ColumnLimit: 100
CommentPragmas: '^ IWYU pragma:'
CompactNamespaces: false
ConstructorInitializerAllOnOneLineOrOnePerLine: false
ConstructorInitializerIndentWidth: 8
ContinuationIndentWidth: 8
Cpp11BracedListStyle: true
DeriveLineEnding: true
DerivePointerAlignment: false
DisableFormat: false
EmptyLineAfterAccessModifier: Never
EmptyLineBeforeAccessModifier: LogicalBlock
ExperimentalAutoDetectBinPacking: false
FixNamespaceComments: false
ForEachMacros:
  - LIST_FOREACH
  - LIST_FOREACH_SAFE
  - RTE_ETH_FOREACH_DEV
  - RTE_LCORE_FOREACH
  - SLIST_FOREACH
  - SLIST_FOREACH_SAFE
  - STAILQ_FOREACH
  - STAILQ_FOREACH_SAFE
  - TAILQ_FOREACH
  - TAILQ_FOREACH_SAFE
  - rte_graph_foreach_node
  - gr_vec_foreach
  - gr_vec_foreach_ref
  - gr_nh_flags_foreach
IfMacros:
  - KJ_IF_MAYBE
IncludeBlocks: Regroup
IncludeCategories:
  - Regex:           '^".*'
    Priority:        -1
  - Regex:           '^<(gr_|gr\.)'
    Priority:        100
  - Regex:           '^<(rte_|event|ecoli|numa.h|libsmartcols.h)'
    Priority:        500
  - Regex:           '^<cmocka'
    Priority:        100000
  - Regex:           '^<'
    Priority:        10000
IncludeIsMainRegex: '(Test)?$'
IncludeIsMainSourceRegex: ''
IndentAccessModifiers: false
IndentCaseBlocks: false
IndentCaseLabels: false
IndentExternBlock: AfterExternBlock
IndentGotoLabels: false
IndentPPDirectives: None
IndentRequires: false
IndentWidth: 8
IndentWrappedFunctionNames: false
InsertTrailingCommas: Wrapped
KeepEmptyLinesAtTheStartOfBlocks: false
LambdaBodyIndentation: Signature
MacroBlockBegin: ''
MacroBlockEnd:   ''
MaxEmptyLinesToKeep: 1
NamespaceIndentation: Inner
ObjCBinPackProtocolList: Auto
ObjCBlockIndentWidth: 4
ObjCBreakBeforeNestedBlockParam: true
ObjCSpaceAfterProperty: true
ObjCSpaceBeforeProtocolList: true
PPIndentWidth: -1
PackConstructorInitializers: BinPack
PenaltyBreakAssignment: 100000000
PenaltyBreakBeforeFirstCallParameter: 0
PenaltyBreakComment: 20
PenaltyBreakFirstLessLess: 120
PenaltyBreakOpenParenthesis: 400
PenaltyBreakString: 100
PenaltyBreakTemplateDeclaration: 10
PenaltyExcessCharacter: 100000
PenaltyIndentedWhitespace: 1000
PenaltyReturnTypeOnItsOwnLine: 100
PointerAlignment: Right
QualifierAlignment: Leave
ReferenceAlignment: Pointer
ReflowComments: false
RemoveBracesLLVM: false
SeparateDefinitionBlocks: Leave
ShortNamespaceLines: 1
SortIncludes: CaseSensitive
SortUsingDeclarations: true
SpaceAfterCStyleCast: false
SpaceAfterLogicalNot: false
SpaceAfterTemplateKeyword: true
SpaceAroundPointerQualifiers: Default
SpaceBeforeAssignmentOperators: true
SpaceBeforeCaseColon: false
SpaceBeforeCpp11BracedList: true
SpaceBeforeCtorInitializerColon: true
SpaceBeforeInheritanceColon: true
SpaceBeforeParens: ControlStatements
SpaceBeforeParensOptions:
  AfterControlStatements: true
  AfterForeachMacros: true
  AfterFunctionDeclarationName: false
  AfterFunctionDefinitionName: false
  AfterIfMacros: true
  BeforeNonEmptyParentheses: false
SpaceBeforeRangeBasedForLoopColon: true
SpaceBeforeSquareBrackets: false
SpaceInEmptyBlock: true
SpaceInEmptyParentheses: false
SpacesBeforeTrailingComments: 1
SpacesInAngles: Never
SpacesInCStyleCastParentheses: false
SpacesInConditionalStatement: false
SpacesInContainerLiterals: true
SpacesInLineCommentPrefix:
  Minimum: 1
  Maximum: -1
SpacesInParentheses: false
SpacesInSquareBrackets: false
Standard: c++20
StatementAttributeLikeMacros:
  - Q_EMIT
StatementMacros:
  - Q_UNUSED
  - QT_REQUIRE_VERSION
TabWidth: 8
UseCRLF: false
UseTab: Always
WhitespaceSensitiveMacros:
  - BOOST_PP_STRINGIZE
  - CF_SWIFT_NAME
  - NS_SWIFT_NAME
  - PP_STRINGIZE
  - STRINGIZE
...

</details>

And this example file (formatted with clang-format 19):

#include <stddef.h>
#include <stdint.h>

#define ICMP6_ERR_DEST_UNREACH 2

struct rte_mbuf;
struct icmp6_err_dest_unreach {
	int foo;
};

char *rte_pktmbuf_prepend(struct rte_mbuf *m, uint16_t len);

void test(struct rte_mbuf *mbuf, int icmp_type);

void test(struct rte_mbuf *mbuf, int icmp_type) {
	struct icmp6_err_dest_unreach *du;
	if (mbuf != NULL) {
		switch (icmp_type) {
                case ICMP6_ERR_DEST_UNREACH:
			du = (struct icmp6_err_dest_unreach *)
				rte_pktmbuf_prepend(mbuf, sizeof(*du));
                        break;
		}
	}
}

When formatting it with clang-format 20 (same configuration), I get a different result:

--- clang-format-19.c
+++ clang-format-20.c
@@ -17,8 +17,8 @@ void test(struct rte_mbuf *mbuf, int icm
        if (mbuf != NULL) {
                switch (icmp_type) {
                case ICMP6_ERR_DEST_UNREACH:
-                       du = (struct icmp6_err_dest_unreach *)
-                               rte_pktmbuf_prepend(mbuf, sizeof(*du));
+                       du = (struct icmp6_err_dest_unreach *
+                       )rte_pktmbuf_prepend(mbuf, sizeof(*du));
                        break;
                }
        }

Maybe I missed a new option but, this looks like a bug/regression.

[tuliom]

This still reproduces when the settings are reduced to:
clang-format --style="{IndentWidth: 8, AlignAfterOpenBracket: BlockIndent}" test.c

[owenca]

It works on main.

[rjarry]

Could you identify which commit fixed the issue?

I am using the stable 20 version and it would be great to back port the fix.

Thanks

[owenca]

Yeah, it breaks in 20.12, but I don't know which commit fixed it off the top of my head.

[rjarry]

Can we keep this issue open for back port in the 20 stable branch?