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Implement missing #elif support to the preprocess_c_code() function. #26054

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Merged
juj merged 1 commit into from
Jan 9, 2026
Merged

Implement missing #elif support to the preprocess_c_code() function. #26054

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8 changes: 8 additions & 0 deletions src/lib/libc_preprocessor.js
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Original file line number Diff line number Diff line change
Expand Up @@ -247,6 +247,14 @@ addToLibrary({
var evaluated = exprTree();
stack.push(!!evaluated * stack[stack.length-1]);
break;
case 'elif':
var tokens = tokenize(expandMacros(expression, 0));
var exprTree = buildExprTree(tokens);
var evaluated = exprTree();
// If the previous #if / #elif block was executed, output NaN so that all further #elif and #else blocks will
// short to false.
stack[stack.length-1] = !!evaluated * (stack[stack.length-1] ? NaN : 1-stack[stack.length-1]);
break;
case 'ifdef': stack.push(!!defs[expression] * stack[stack.length-1]); break;
case 'ifndef': stack.push(!defs[expression] * stack[stack.length-1]); break;
case 'else': stack[stack.length-1] = (1-stack[stack.length-1]) * stack[stack.length-2]; break;
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5 changes: 5 additions & 0 deletions test/test_c_preprocessor.c
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Expand Up @@ -191,6 +191,11 @@ EM_JS(void, test_c_preprocessor, (void), {

test('#line 162 "foo.glsl"\n', '#line 162 "foo.glsl"\n'); // Test that #line directives are retained in the output

test('#define FOO 1\n#ifdef FOO\nA\n#elif defined(BAR)\nB\n#elif defined(BAZ)\nC\n#else\nD\n#endif', "A\n"); // Test #elif support, taking #ifdef path
test('#define BAR 1\n#ifdef FOO\nA\n#elif defined(BAR)\nB\n#elif defined(BAZ)\nC\n#else\nD\n#endif', "B\n"); // Test #elif support, taking first #elif path
test('#define BAZ 1\n#ifdef FOO\nA\n#elif defined(BAR)\nB\n#elif defined(BAZ)\nC\n#else\nD\n#endif', "C\n"); // Test #elif support, taking a second #elif path
test( '#ifdef FOO\nA\n#elif defined(BAR)\nB\n#elif defined(BAZ)\nC\n#else\nD\n#endif', "D\n"); // Test #elif support, taking the final #else path

if (numFailed) throw numFailed + ' tests failed!';
});

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