This is for whomever maintains the discourse server. I know @jonah has helped in the past.
Discourse uses highlight.js and Stan highlighting updates were recently merged. Highlight.js has not made a new release but once it does we can ping Discourse to pull in the recent update.
If we want, we can test a manual update (not sure it will work unless we build the entire thing, though that’s pretty easy as well) to the Discourse code at https://github.com/discourse/discourse/blob/main/vendor/assets/javascripts/highlightjs/language/stan.min.js and replacing with the updated stan.min.js which I compiled on my computer:
stan.min.js file
/*! `stan` grammar compiled for Highlight.js 11.3.1 */
var hljsGrammar=(()=>{"use strict";return e=>{
const _=e.regex,o=["bernoulli","bernoulli_logit","bernoulli_logit_glm","beta","beta_binomial","beta_proportion","binomial","binomial_logit","categorical","categorical_logit","categorical_logit_glm","cauchy","chi_square","dirichlet","discrete_range","double_exponential","exp_mod_normal","exponential","frechet","gamma","gaussian_dlm_obs","gumbel","hmm_latent","hypergeometric","inv_chi_square","inv_gamma","inv_wishart","lkj_corr","lkj_corr_cholesky","logistic","lognormal","multi_gp","multi_gp_cholesky","multi_normal","multi_normal_cholesky","multi_normal_prec","multi_student_t","multinomial","multinomial_logit","neg_binomial","neg_binomial_2","neg_binomial_2_log","neg_binomial_2_log_glm","normal","normal_id_glm","ordered_logistic","ordered_logistic_glm","ordered_probit","pareto","pareto_type_2","poisson","poisson_log","poisson_log_glm","rayleigh","scaled_inv_chi_square","skew_double_exponential","skew_normal","std_normal","student_t","uniform","von_mises","weibull","wiener","wishart"],r=e.COMMENT(/\/\*/,/\*\//,{
relevance:0,contains:[{scope:"doctag",match:/@(return|param)/}]}),i={
scope:"meta",begin:/#include\b/,end:/$/,contains:[{match:/[a-z][a-z-._]+/,
scope:"string"},e.C_LINE_COMMENT_MODE]
},t=["lower","upper","offset","multiplier"];return{name:"Stan",
aliases:["stanfuncs"],keywords:{$pattern:e.IDENT_RE,
title:["functions","model","data","parameters","quantities","transformed","generated"],
type:["array","complex","int","real","vector","ordered","positive_ordered","simplex","unit_vector","row_vector","matrix","cholesky_factor_corr|10","cholesky_factor_cov|10","corr_matrix|10","cov_matrix|10","void"],
keyword:["for","in","if","else","while","break","continue","return"],
built_in:["Phi","Phi_approx","abs","acos","acosh","add_diag","algebra_solver","algebra_solver_newton","append_array","append_col","append_row","asin","asinh","atan","atan2","atanh","bessel_first_kind","bessel_second_kind","binary_log_loss","binomial_coefficient_log","block","cbrt","ceil","chol2inv","cholesky_decompose","choose","col","cols","columns_dot_product","columns_dot_self","conj","cos","cosh","cov_exp_quad","crossprod","csr_extract_u","csr_extract_v","csr_extract_w","csr_matrix_times_vector","csr_to_dense_matrix","cumulative_sum","determinant","diag_matrix","diag_post_multiply","diag_pre_multiply","diagonal","digamma","dims","distance","dot_product","dot_self","eigenvalues_sym","eigenvectors_sym","erf","erfc","exp","exp2","expm1","fabs","falling_factorial","fdim","floor","fma","fmax","fmin","fmod","gamma_p","gamma_q","generalized_inverse","get_imag","get_lp","get_real","head","hmm_hidden_state_prob","hmm_marginal","hypot","identity_matrix","inc_beta","int_step","integrate_1d","integrate_ode","integrate_ode_adams","integrate_ode_bdf","integrate_ode_rk45","inv","inv_Phi","inv_cloglog","inv_logit","inv_sqrt","inv_square","inverse","inverse_spd","is_inf","is_nan","lambert_w0","lambert_wm1","lbeta","lchoose","ldexp","lgamma","linspaced_array","linspaced_int_array","linspaced_row_vector","linspaced_vector","lmgamma","lmultiply","log","log1m","log1m_exp","log1m_inv_logit","log1p","log1p_exp","log_determinant","log_diff_exp","log_falling_factorial","log_inv_logit","log_inv_logit_diff","log_mix","log_modified_bessel_first_kind","log_rising_factorial","log_softmax","log_sum_exp","logit","machine_precision","map_rect","matrix_exp","matrix_exp_multiply","matrix_power","max","mdivide_left_spd","mdivide_left_tri_low","mdivide_right_spd","mdivide_right_tri_low","mean","min","modified_bessel_first_kind","modified_bessel_second_kind","multiply_log","multiply_lower_tri_self_transpose","negative_infinity","norm","not_a_number","num_elements","ode_adams","ode_adams_tol","ode_adjoint_tol_ctl","ode_bdf","ode_bdf_tol","ode_ckrk","ode_ckrk_tol","ode_rk45","ode_rk45_tol","one_hot_array","one_hot_int_array","one_hot_row_vector","one_hot_vector","ones_array","ones_int_array","ones_row_vector","ones_vector","owens_t","polar","positive_infinity","pow","print","prod","proj","qr_Q","qr_R","qr_thin_Q","qr_thin_R","quad_form","quad_form_diag","quad_form_sym","quantile","rank","reduce_sum","reject","rep_array","rep_matrix","rep_row_vector","rep_vector","reverse","rising_factorial","round","row","rows","rows_dot_product","rows_dot_self","scale_matrix_exp_multiply","sd","segment","sin","singular_values","sinh","size","softmax","sort_asc","sort_desc","sort_indices_asc","sort_indices_desc","sqrt","square","squared_distance","step","sub_col","sub_row","sum","svd_U","svd_V","symmetrize_from_lower_tri","tail","tan","tanh","target","tcrossprod","tgamma","to_array_1d","to_array_2d","to_complex","to_matrix","to_row_vector","to_vector","trace","trace_gen_quad_form","trace_quad_form","trigamma","trunc","uniform_simplex","variance","zeros_array","zeros_int_array","zeros_row_vector"]
},contains:[e.C_LINE_COMMENT_MODE,i,e.HASH_COMMENT_MODE,r,{scope:"built_in",
match:/\s(pi|e|sqrt2|log2|log10)(?=\()/,relevance:0},{
match:_.concat(/[<,]\s*/,_.either(...t),/\s*=/),keywords:t},{scope:"keyword",
match:/\btarget(?=\s*\+=)/},{
match:[/~\s*/,_.either(...o),/(?:\(\))/,/\s*T(?=\s*\[)/],scope:{2:"built_in",
4:"keyword"}},{scope:"built_in",keywords:o,
begin:_.concat(/\w*/,_.either(...o),/(_lpdf|_lupdf|_lpmf|_cdf|_lcdf|_lccdf|_qf)(?=\s*[\(.*\)])/)
},{begin:[/~/,/\s*/,_.concat(_.either(...o),/(?=\s*[\(.*\)])/)],scope:{
3:"built_in"}},{
begin:[/~/,/\s*\w+(?=\s*[\(.*\)])/,"(?!.*/\b("+_.either(...o)+")\b)"],scope:{
2:"title.function"}},{scope:"title.function",
begin:/\w*(_lpdf|_lupdf|_lpmf|_cdf|_lcdf|_lccdf|_qf)(?=\s*[\(.*\)])/},{
scope:"number",
match:_.concat(/(?:\b\d+(?:_\d+)*(?:\.(?:\d+(?:_\d+)*)?)?|\B\.\d+(?:_\d+)*)/,/(?:[eE][+-]?\d+(?:_\d+)*)?i?(?!\w)/),
relevance:0},{scope:"string",begin:/"/,end:/"/}]}}})()
;export default hljsGrammar;
Note: To build the cdn highlight.js files that mimic the discourse ones. Git clone the highlight.js repo then cd into it and run node ./tools/build.js -t cdn :common stan. Assuming node/npm are setup.