Style: indent preprocessor directives

.clang-format

@@ -75,7 +75,8 @@ IncludeCategories:
     Priority:        1
 IncludeIsMainRegex: '(Test)?$'
 IndentCaseLabels: true
-IndentPPDirectives: None
+IndentPPDirectives: AfterHash
+PPIndentWidth: -1
 IndentWidth:     4
 IndentWrappedFunctionNames: false
 InsertBraces: true

.github/workflows/check-formatting.yaml

@@ -36,11 +36,8 @@ jobs:
 
     - name: "Install run-clang-format"
       run: |
-        wget -q -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
-        echo "deb http://apt.llvm.org/focal/ llvm-toolchain-focal-16 main" | sudo tee -a /etc/apt/sources.list
-        echo "deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal-16 main" | sudo tee -a /etc/apt/sources.list
         sudo apt-get update
-        sudo apt-get install -y clang-format-16
+        sudo apt-get install -y clang-format-20
         curl -sSfL https://raw.githubusercontent.com/Sarcasm/run-clang-format/master/run-clang-format.py -o run-clang-format
         chmod +x run-clang-format
 

C_CODING_STYLE.md

@@ -107,6 +107,38 @@ void f(bool reverse) {
 }
 ```
 
+### Preprocessor Indentation
+
+Indent nested preprocessor directives after the hash mark [AVMCCS-F022]:
+- The hash `#` stays in column 1, directives are indented with 4 spaces after the hash
+- Each nesting level adds 4 spaces after the `#`
+- **Exception**: Include guards do not count for indentation. The guard directives themselves
+(`#ifndef`, `#define`, `#endif`) and all content between them remain at column 1
+
+Good:
+
+```c
+#ifdef USE_POSITIVE_NUMBERS
+#    define A 1
+#    define B 2
+#else
+#    define A -1
+#    define B -2
+#endif
+```
+
+Bad:
+
+```c
+#ifdef USE_POSITIVE_NUMBERS
+#define A 1
+#define B 2
+#else
+#define A -1
+#define B -2
+#endif
+```
+
 ## Formatting
 
 ### General Rules
@@ -2428,6 +2460,7 @@ This convention system creates self-documenting code where the naming pattern im
 |------|-------------|---------|
 | Braces | K&R variant (new line for functions/types) | `void f(void)\n{` |
 | Indentation | 4 spaces, no tabs | `    if (x) {` |
+| Preprocessor indent | After hash, except include guards | `#ifdef X\n#    define Y 1\n#endif` |
 | Pointer `*` | With variable name | `char *name` not `char* name` |
 | Line length | < 100 columns | Use intermediate variables |
 | Hex numbers | Uppercase letters | `0xDEADBEEF` not `0xdeadbeef` |
@@ -2739,7 +2772,9 @@ This style guide can be largely enforced using clang-format. Create a `.clang-fo
 
 BasedOnStyle: LLVM
 
-# Indentation (rules: AVMCCS-F003)
+# Indentation (rules: AVMCCS-F003, AVMCCS-F022)
+IndentPPDirectives: AfterHash
+PPIndentWidth: -1
 IndentWidth: 4
 TabWidth: 4
 UseTab: Never
@@ -3423,6 +3458,7 @@ This section provides a complete index of all rules defined in this style guide,
 | AVMCCS-F019 | Use uppercase letters for hexadecimal numbers | Spacing |
 | AVMCCS-F020 | Use spaces around binary operators | Spacing |
 | AVMCCS-F021 | Always place initializer braces on the same line as declaration | Spacing |
+| AVMCCS-F022 | Indent nested preprocessor directives after the hash mark | Style Rules |
 | **Naming** | | |
 | AVMCCS-N001 | Preserve word boundaries when converting between casing styles | Word Boundary Preservation |
 | AVMCCS-N002 | Keep acronyms capitalized in PascalCase; treat as single word when converting | Word Boundary Preservation |
@@ -3519,8 +3555,16 @@ This section provides a complete index of all rules defined in this style guide,
 | AVMCCS-S005 | Group includes by origin with alphabetical ordering | Include Ordering |
 | AVMCCS-S006 | Header files match module names using underscores | Header File Naming |
 
+## Changes
+
+### Version 1.1
+
+**Preprocessor Indentation** (AVMCCS-F022):
+- Nested preprocessor directives now indent after the hash mark (exception: include guards remain
+unindented for clarity)
+
 ---
 
-*Document Version*: 1.0
+*Document Version*: 1.1
 *Style Guide Name*: AtomVM C Coding Style Guide (AVMCCS Guide)
-*Last Updated*: July 2025
+*Last Updated*: November 2025

src/libAtomVM/atom_table.c

@@ -31,13 +31,13 @@
 #include "utils.h"
 
 #ifndef AVM_NO_SMP
-#define SMP_RDLOCK(htable) smp_rwlock_rdlock(htable->lock)
-#define SMP_WRLOCK(htable) smp_rwlock_wrlock(htable->lock)
-#define SMP_UNLOCK(htable) smp_rwlock_unlock(htable->lock)
+#    define SMP_RDLOCK(htable) smp_rwlock_rdlock(htable->lock)
+#    define SMP_WRLOCK(htable) smp_rwlock_wrlock(htable->lock)
+#    define SMP_UNLOCK(htable) smp_rwlock_unlock(htable->lock)
 #else
-#define SMP_RDLOCK(htable) UNUSED(htable)
-#define SMP_WRLOCK(htable) UNUSED(htable)
-#define SMP_UNLOCK(htable) UNUSED(htable)
+#    define SMP_RDLOCK(htable) UNUSED(htable)
+#    define SMP_WRLOCK(htable) UNUSED(htable)
+#    define SMP_UNLOCK(htable) UNUSED(htable)
 #endif
 
 #define DEFAULT_SIZE 8
@@ -427,7 +427,7 @@ static inline int read_encoded_len(const uint8_t **len_bytes)
 }
 
 // -1 is not a valid atom index as we're limited to 2^20
-#define ATOM_TABLE_NOT_FOUND_MARKER ((atom_index_t) -1)
+#define ATOM_TABLE_NOT_FOUND_MARKER ((atom_index_t) - 1)
 
 enum AtomTableEnsureAtomResult atom_table_ensure_atoms(struct AtomTable *table, const void *atoms, size_t count,
     atom_index_t *translate_table, enum EnsureAtomsOpt opt)

src/libAtomVM/bif.c

@@ -72,11 +72,11 @@
  * do not use `(avm_float_t) INT64_MIN` or `(avm_float_t) INT64_MAX`.
  */
 #ifdef AVM_USE_SINGLE_PRECISION
-#define INT64_MIN_AS_AVM_FLOAT -9223372586610590720.0 // 0xDF000000 = -2^63
-#define INT64_MAX_AS_AVM_FLOAT 9223371761976868863.0 // 0x5F000000 = 2^63
+#    define INT64_MIN_AS_AVM_FLOAT -9223372586610590720.0 // 0xDF000000 = -2^63
+#    define INT64_MAX_AS_AVM_FLOAT 9223371761976868863.0 // 0x5F000000 = 2^63
 #else
-#define INT64_MIN_AS_AVM_FLOAT -9223372036854776832.0 // 0xC3E0000000000000 = -2^63
-#define INT64_MAX_AS_AVM_FLOAT 9223372036854775295.0 // 0x43DFFFFFFFFFFFFF = 2^62 * 1.1...1b
+#    define INT64_MIN_AS_AVM_FLOAT -9223372036854776832.0 // 0xC3E0000000000000 = -2^63
+#    define INT64_MAX_AS_AVM_FLOAT 9223372036854775295.0 // 0x43DFFFFFFFFFFFFF = 2^62 * 1.1...1b
 #endif
 
 const struct ExportedFunction *bif_registry_get_handler(const char *mfa)
@@ -645,7 +645,7 @@ static term add_boxed_helper(Context *ctx, uint32_t fail_label, uint32_t live, t
 #elif BOXED_TERMS_REQUIRED_FOR_INT64 == 1
                     return add_int64_to_bigint(ctx, fail_label, live, val1, val2);
 #else
-#error "Unsupported configuration."
+#    error "Unsupported configuration."
 #endif
                 }
 
@@ -784,7 +784,7 @@ static term sub_boxed_helper(Context *ctx, uint32_t fail_label, uint32_t live, t
 #elif BOXED_TERMS_REQUIRED_FOR_INT64 == 1
                     return sub_int64_to_bigint(ctx, fail_label, live, val1, val2);
 #else
-#error "Unsupported configuration."
+#    error "Unsupported configuration."
 #endif
                 }
 
@@ -927,7 +927,7 @@ static term mul_boxed_helper(Context *ctx, uint32_t fail_label, uint32_t live, t
 #elif BOXED_TERMS_REQUIRED_FOR_INT64 == 1
                     return mul_int64_to_bigint(ctx, fail_label, live, val1, val2);
 #else
-#error "Unsupported configuration."
+#    error "Unsupported configuration."
 #endif
                 }
 
@@ -1177,7 +1177,7 @@ static term neg_boxed_helper(Context *ctx, uint32_t fail_label, uint32_t live, t
                         return int64_max_plus_one(ctx, fail_label, live);
 
 #else
-#error "Unsupported configuration."
+#    error "Unsupported configuration."
 #endif
 
                     default:
@@ -1279,7 +1279,7 @@ static term abs_boxed_helper(Context *ctx, uint32_t fail_label, uint32_t live, t
                     return int64_max_plus_one(ctx, fail_label, live);
 
 #else
-#error "Unsupported configuration."
+#    error "Unsupported configuration."
 #endif
 
                 } else {

src/libAtomVM/bitstring.c

@@ -26,7 +26,14 @@
 
 static inline uint64_t from_le64(uint64_t value)
 {
-    return ((((value) &0xFF) << 56) | (((value) &0xFF00) << 40) | (((value) &0xFF0000) << 24) | (((value) &0xFF000000) << 8) | (((value) &0xFF00000000) >> 8) | (((value) &0xFF0000000000) >> 24) | (((value) &0xFF000000000000) >> 40) | (((value) &0xFF00000000000000) >> 56));
+    return ((((value) & 0xFF) << 56)
+        | (((value) & 0xFF00) << 40)
+        | (((value) & 0xFF0000) << 24)
+        | (((value) & 0xFF000000) << 8)
+        | (((value) & 0xFF00000000) >> 8)
+        | (((value) & 0xFF0000000000) >> 24)
+        | (((value) & 0xFF000000000000) >> 40)
+        | (((value) & 0xFF00000000000000) >> 56));
 }
 
 bool bitstring_extract_any_integer(const uint8_t *src, size_t offset, avm_int_t n,

src/libAtomVM/context.c

@@ -38,12 +38,12 @@
 #include "utils.h"
 
 #ifdef HAVE_PLATFORM_ATOMIC_H
-#include "platform_atomic.h"
+#    include "platform_atomic.h"
 #else
-#if defined(HAVE_ATOMIC)
-#include <stdatomic.h>
-#define ATOMIC_COMPARE_EXCHANGE_WEAK_INT atomic_compare_exchange_weak
-#endif
+#    if defined(HAVE_ATOMIC)
+#        include <stdatomic.h>
+#        define ATOMIC_COMPARE_EXCHANGE_WEAK_INT atomic_compare_exchange_weak
+#    endif
 #endif
 
 #define IMPL_EXECUTE_LOOP
@@ -467,15 +467,15 @@ void context_process_code_server_resume_signal(Context *ctx)
     // jit_trap_and_load stores the label in saved_function_ptr
     uint32_t label = (uint32_t) (uintptr_t) ctx->saved_function_ptr;
     Module *module = ctx->saved_module;
-#ifndef AVM_NO_EMU
+#    ifndef AVM_NO_EMU
     if (module->native_code) {
         ctx->saved_function_ptr = module_get_native_entry_point(module, label);
     } else {
         ctx->saved_ip = module->labels[label];
     }
-#else
+#    else
     ctx->saved_function_ptr = module_get_native_entry_point(module, label);
-#endif
+#    endif
     // Fix CP to OP_INT_CALL_END
     if (ctx->cp == module_address(module->module_index, 0)) {
         ctx->cp = module_address(module->module_index, module->end_instruction_ii);

src/libAtomVM/context.h

@@ -43,7 +43,7 @@ extern "C" {
 struct Module;
 
 #ifndef TYPEDEF_MODULE
-#define TYPEDEF_MODULE
+#    define TYPEDEF_MODULE
 typedef struct Module Module;
 #endif
 
@@ -160,7 +160,7 @@ struct Context
 };
 
 #ifndef TYPEDEF_CONTEXT
-#define TYPEDEF_CONTEXT
+#    define TYPEDEF_CONTEXT
 typedef struct Context Context;
 #endif
 

src/libAtomVM/debug.h

@@ -95,9 +95,9 @@ char reg_type_c(int reg_type);
 void debug_print_processes_list(struct ListHead *processes);
 
 #ifdef ENABLE_STACK_TRACE
-#define DEBUG_DUMP_STACK debug_dump_stack
+#    define DEBUG_DUMP_STACK debug_dump_stack
 #else
-#define DEBUG_DUMP_STACK(...)
+#    define DEBUG_DUMP_STACK(...)
 #endif
 
 #ifdef __cplusplus

src/libAtomVM/ets.c

@@ -32,20 +32,20 @@
 #define ETS_ANY_PROCESS -1
 
 #ifndef AVM_NO_SMP
-#define SMP_RDLOCK(table) smp_rwlock_rdlock(table->lock)
-#define SMP_WRLOCK(table) smp_rwlock_wrlock(table->lock)
-#define SMP_UNLOCK(table) smp_rwlock_unlock(table->lock)
+#    define SMP_RDLOCK(table) smp_rwlock_rdlock(table->lock)
+#    define SMP_WRLOCK(table) smp_rwlock_wrlock(table->lock)
+#    define SMP_UNLOCK(table) smp_rwlock_unlock(table->lock)
 #else
-#define SMP_RDLOCK(table)
-#define SMP_WRLOCK(table)
-#define SMP_UNLOCK(table)
+#    define SMP_RDLOCK(table)
+#    define SMP_WRLOCK(table)
+#    define SMP_UNLOCK(table)
 #endif
 
 #ifndef AVM_NO_SMP
-#ifndef TYPEDEF_RWLOCK
-#define TYPEDEF_RWLOCK
+#    ifndef TYPEDEF_RWLOCK
+#        define TYPEDEF_RWLOCK
 typedef struct RWLock RWLock;
-#endif
+#    endif
 #endif
 
 struct EtsTable

src/libAtomVM/exportedfunction.h

@@ -31,17 +31,17 @@
 #include "term.h"
 
 #ifndef TYPEDEF_MODULE
-#define TYPEDEF_MODULE
+#    define TYPEDEF_MODULE
 typedef struct Module Module;
 #endif
 
 #ifndef TYPEDEF_MODULENATIVEINTERFACE
-#define TYPEDEF_MODULENATIVEINTERFACE
+#    define TYPEDEF_MODULENATIVEINTERFACE
 typedef struct ModuleNativeInterface ModuleNativeInterface;
 #endif
 
 #ifndef TYPEDEF_JITSTATE
-#define TYPEDEF_JITSTATE
+#    define TYPEDEF_JITSTATE
 typedef struct JITState JITState;
 #endif
 

src/libAtomVM/externalterm.c

@@ -1157,7 +1157,7 @@ static int calculate_heap_usage(const uint8_t *external_term_buf, size_t remaini
 #elif TERM_BYTES == 8
             int size_in_terms = ((binary_size + 8 - 1) >> 3);
 #else
-#error
+#    error
 #endif
 
             if (copy && term_binary_size_is_heap_binary(binary_size)) {