diff --git a/R/document.R b/R/document.R
index 60fd0f00..48a29580 100644
--- a/R/document.R
+++ b/R/document.R
@@ -186,122 +186,204 @@ get_range_text <- function(content, line1, col1, line2, col2) {
     lines
 }
 
-parse_expr <- function(content, expr, env, level = 0L, srcref = attr(expr, "srcref")) {
-    if (length(expr) == 0L || is.symbol(expr)) {
-          return(env)
-    }
-    # We should handle base function specially as users may use base::fun form
-    # The reason that we only take care of `base` (not `utils`) is that only `base` calls can generate symbols
-    # Check if the lang is in base::fun form
-    is_base_call <- function(x) {
-        length(x) == 3L && as.character(x[[1L]]) %in% c("::", ":::") && as.character(x[[2L]]) == "base"
-    }
-    # Be able to handle `pkg::name` case (note `::` is a function)
-    is_symbol <- function(x) {
-        is.symbol(x) || is_base_call(x)
-    }
-    # Handle `base` function specically by removing the `base::` prefix
-    fun_string <- function(x) {
-        if (is_base_call(x)) as.character(x[[3L]]) else as.character(x)
-    }
-    for (i in seq_along(expr)) {
-        e <- expr[[i]]
-        if (missing(e) || !is.call(e) || !is_symbol(e[[1L]])) next
-        f <- fun_string(e[[1L]])
-        cur_srcref <- if (level == 0L) srcref[[i]] else srcref
-        if (f %in% c("{", "(")) {
-            Recall(content, e[-1L], env, level + 1L, cur_srcref)
-        } else if (f == "if") {
-            Recall(content, e[[2L]], env, level + 1L, cur_srcref)
-            Recall(content, e[[3L]], env, level + 1L, cur_srcref)
-            if (length(e) == 4L) {
-                Recall(content, e[[4L]], env, level + 1L, cur_srcref)
-            }
-        } else if (f == "for") {
-            if (is.symbol(e[[2L]])) {
-                env$nonfuncts <- c(env$nonfuncts, as.character(e[[2L]]))
-            }
-            Recall(content, e[[4L]], env, level + 1L, cur_srcref)
-        } else if (f == "while") {
-            Recall(content, e[[2L]], env, level + 1L, cur_srcref)
-            Recall(content, e[[3L]], env, level + 1L, cur_srcref)
-        } else if (f == "repeat") {
-            Recall(content, e[[2L]], env, level + 1L, cur_srcref)
-        } else if (f %in% c("<-", "=", "delayedAssign", "makeActiveBinding", "assign")) {
-            # to see the pos/env/assign.env of assigning functions is set or not
-            # if unset, it means using the default value, which is top-level
-            # if set, we should compare to a vector of known "top-level" candidates
-            is_top_level <- function(arg_env, ...) {
-                if (is.null(arg_env)) return(TRUE)
-                default <- list(
-                    quote(parent.frame(1)), quote(parent.frame(1L)),
-                    quote(environment()),
-                    quote(.GlobalEnv), quote(globalenv())
-                )
-                extra <- substitute(list(...))[-1L]
-                top_level_envs <- c(default, as.list(extra))
-                any(vapply(top_level_envs, identical, x = arg_env, FUN.VALUE = logical(1L)))
-            }
+is_ns_call <- function(x) {
+    length(x) == 3L && is.symbol(x[[1L]]) && as.character(x[[1L]]) %in% c("::", ":::")
+}
 
-            type <- NULL
-
-            if (f %in% c("<-", "=")) {
-                if (length(e) != 3L || !is.symbol(e[[2L]])) next
-                symbol <- as.character(e[[2L]])
-                value <- e[[3L]]
-            } else if (f == "delayedAssign") {
-                call <- match.call(base::delayedAssign, as.call(e))
-                if (!is.character(call$x)) next
-                if (!is_top_level(call$assign.env)) next
-                symbol <- call$x
-                value <- call$value
-            } else if (f == "assign") {
-                call <- match.call(base::assign, as.call(e))
-                if (!is.character(call$x)) next
-                if (!is_top_level(call$pos, -1L, -1)) next # -1 is the default
-                if (!is_top_level(call$envir)) next
-                symbol <- call$x
-                value <- call$value
-            } else if (f == "makeActiveBinding") {
-                call <- match.call(base::makeActiveBinding, as.call(e))
-                if (!is.character(call$sym)) next
-                if (!is_top_level(call$env)) next
-                symbol <- call$sym
-                value <- call$fun
-                type <- "variable"
-            }
+# Check if an expression is a simple call like `foo(bar)` or `pkg::foo(bar)`
+# This rules out anonymous function call like `(function(x) x + 1)(bar)`
+is_simple_call <- function(x) {
+    is.call(x) && (is.symbol(x[[1L]]) || is_ns_call(x[[1]]))
+}
 
-            if (is.null(type)) {
-                type <- get_expr_type(value)
-            }
+# We should handle base function specially as users may use base::fun form
+# The reason that we only take care of `base` (not `utils`) is that only `base` calls can generate symbols
+# Check if the lang is in base::fun form
+is_base_call <- function(x) {
+    is_ns_call(x) && as.character(x[[2L]]) == "base"
+}
 
-            env$objects <- c(env$objects, symbol)
+# Handle `base` function specically by removing the `base::` prefix
+fun_string <- function(x) {
+    if (is_base_call(x)) as.character(x[[3L]]) else deparse(x)
+}
 
-            expr_range <- expr_range(cur_srcref)
-            env$definitions[[symbol]] <- list(
-                name = symbol,
-                type = type,
-                range = expr_range
-            )
+# to see the pos/env/assign.env of assigning functions is set or not
+# if unset, it means using the default value, which is top-level
+# if set, we should compare to a vector of known "top-level" candidates
+is_top_level <- function(arg_env, ...) {
+    if (is.null(arg_env)) return(TRUE)
+    default <- list(
+        quote(parent.frame(1)), quote(parent.frame(1L)),
+        quote(environment()),
+        quote(.GlobalEnv), quote(globalenv())
+    )
+    extra <- substitute(list(...))[-1L]
+    top_level_envs <- c(default, as.list(extra))
+    any(vapply(top_level_envs, identical, x = arg_env, FUN.VALUE = logical(1L)))
+}
 
-            doc_line1 <- detect_comments(content, expr_range$start$line) + 1
-            if (doc_line1 <= expr_range$start$line) {
-                comment <- content[seq.int(doc_line1, expr_range$start$line)]
-                env$documentation[[symbol]] <- convert_comment_to_documentation(comment)
-            }
+parser_hooks <- list(
+    "{" = function(expr, action) {
+        action$parse(as.list(expr)[-1L])
+    },
+    "(" = function(expr, action) {
+        action$parse(as.list(expr)[-1L])
+    },
+    "if" = function(expr, action) {
+        action$parse(as.list(expr)[-1L])
+    },
+    "for" = function(expr, action) {
+        if (is.symbol(e <- expr[[2L]])) {
+            action$update(nonfuncts = as.character(e))
+        }
+        action$parse(expr[[4L]])
+    },
+    "while" = function(expr, action) {
+        action$parse(as.list(expr)[-1L])
+    },
+    "repeat" = function(expr, action) {
+        action$parse(expr[[2L]])
+    },
+    "<-" = function(expr, action) {
+        if (length(expr) == 3L && is.symbol(expr[[2L]])) {
+            action$assign(symbol = as.character(expr[[2L]]), value = expr[[3L]])
+            action$parse(expr[[3L]])
+        }
+    },
+    "=" = function(expr, action) {
+        if (length(expr) == 3L && is.symbol(expr[[2L]])) {
+            action$assign(symbol = as.character(expr[[2L]]), value = expr[[3L]])
+            action$parse(expr[[3L]])
+        }
+    },
+    "assign" = function(expr, action) {
+        call <- match.call(base::assign, expr)
+        if (is.character(call$x) && is_top_level(call$pos, -1L, -1) && is_top_level(call$envir)) {
+            action$assign(symbol = call$x, value = call$value)
+            action$parse(call$value)
+        }
+    },
+    "delayedAssign" = function(expr, action) {
+        call <- match.call(base::delayedAssign, expr)
+        if (is.character(call$x) && is_top_level(call$assign.env)) {
+            action$assign(symbol = call$x, value = call$value)
+            action$parse(call$value)
+        }
+    },
+    "makeActiveBinding" = function(expr, action) {
+        call <- match.call(base::makeActiveBinding, expr)
+        if (is.character(call$sym) && is_top_level(call$env)) {
+            action$assign(symbol = call$sym, value = call$fun, type = "variable")
+        }
+    },
+    "library" = function(expr, action) {
+        call <- match.call(base::library, expr)
+        if (!isTRUE(call$character.only)) {
+            action$update(packages = as.character(call$package))
+        }
+    },
+    "require" = function(expr, action) {
+        call <- match.call(base::require, expr)
+        if (!isTRUE(call$character.only)) {
+            action$update(packages = as.character(call$package))
+        }
+    },
+    "pacman::p_load" = function(expr, action) {
+        fun <- if (requireNamespace("pacman")) pacman::p_load else
+            function(..., char, install = TRUE,
+                     update = getOption("pac_update"),
+                     character.only = FALSE) NULL
+        call <- match.call(fun, expr, expand.dots = FALSE)
+        if (!isTRUE(call$character.only)) {
+            packages <- vapply(call[["..."]], as.character, character(1L))
+            action$update(packages = packages)
+        }
+    },
+    "system.time" = function(expr, action) action$parse_args("expr"),
+    "try" = function(expr, action) action$parse_args("expr"),
+    "tryCatch" = function(expr, action) action$parse_args(c("expr", "finally")),
+    "withCallingHandlers" = function(expr, action) action$parse_args("expr"),
+    "withRestarts" = function(expr, action) action$parse_args("expr"),
+    "allowInterrupts" = function(expr, action) action$parse_args("expr"),
+    "suspendInterrupts" = function(expr, action) action$parse_args("expr"),
+    "suppressPackageStartupMessages" = function(expr, action) action$parse_args("expr"),
+    "suppressMessages" = function(expr, action) action$parse_args("expr"),
+    "suppressWarnings" = function(expr, action) action$parse_args("expr")
+)
 
-            if (type == "function") {
-                env$functs <- c(env$functs, symbol)
-                env$formals[[symbol]] <- value[[2L]]
-                env$signatures[[symbol]] <- get_signature(symbol, value)
-            } else {
-                env$nonfuncts <- c(env$nonfuncts, symbol)
-            }
-        } else if (f %in% c("library", "require") && length(e) == 2L) {
-            pkg <- as.character(e[[2L]])
-            if (!(pkg %in% env$packages)) {
-                env$packages <- c(env$packages, pkg)
-            }
+parse_expr <- function(content, expr, env, srcref = attr(expr, "srcref")) {
+    if (length(expr) == 0L || is.symbol(expr) || is.atomic(expr)) {
+        return(env)
+    }
+
+    if (is.expression(expr)) {
+        for (i in seq_along(expr)) {
+            Recall(content, expr[[i]], env, srcref[[i]])
+        }
+    } else if (is.list(expr)) {
+        for (i in seq_along(expr)) {
+            e <- expr[[i]]
+            if (missing(e)) next
+            Recall(content, e, env, srcref)
+        }
+    } else if (is_simple_call(expr)) {
+        f <- fun_string(expr[[1L]])
+        fun <- parser_hooks[[f]]
+        if (is.function(fun)) {
+            action <- list(
+                update = function(...) {
+                    updates <- list(...)
+                    for (name in names(updates)) {
+                        values <- updates[[name]]
+                        values <- values[nzchar(values)]
+                        if (length(values)) {
+                            env[[name]] <- union(env[[name]], values)
+                        }
+                    }
+                },
+                assign = function(symbol, value, type = get_expr_type(value)) {
+                    if (!nzchar(symbol)) return(NULL)
+
+                    env$objects <- c(env$objects, symbol)
+
+                    expr_range <- expr_range(srcref)
+                    env$definitions[[symbol]] <- list(
+                        name = symbol,
+                        type = type,
+                        range = expr_range
+                    )
+
+                    doc_line1 <- detect_comments(content, expr_range$start$line) + 1
+                    if (doc_line1 <= expr_range$start$line) {
+                        comment <- content[seq.int(doc_line1, expr_range$start$line)]
+                        env$documentation[[symbol]] <- convert_comment_to_documentation(comment)
+                    }
+
+                    if (type == "function") {
+                        env$functs <- c(env$functs, symbol)
+                        env$formals[[symbol]] <- value[[2L]]
+                        env$signatures[[symbol]] <- get_signature(symbol, value)
+                    } else {
+                        env$nonfuncts <- c(env$nonfuncts, symbol)
+                    }
+                },
+                parse = function(expr) {
+                    parse_expr(content, expr, env, srcref)
+                },
+                parse_args = function(args) {
+                    fn <- tryCatch(eval(expr[[1L]], globalenv()), error = function(e) NULL)
+                    if (is.function(fn)) {
+                        call <- match.call(fn, expr, expand.dots = FALSE)
+                        for (arg in args) {
+                            if (is.call(call[[arg]])) {
+                                parse_expr(content, call[[arg]], env, srcref)
+                            }
+                        }
+                    }
+                }
+            )
+            tryCatch(fun(expr, action), error = function(e) NULL)
         }
     }
     env
diff --git a/R/zzz.R b/R/zzz.R
new file mode 100644
index 00000000..755d697e
--- /dev/null
+++ b/R/zzz.R
@@ -0,0 +1,5 @@
+.onLoad <- function(...) {
+  user_parser_hooks <- getOption("languageserver.parser_hooks")
+  parser_hooks[names(user_parser_hooks)] <<- user_parser_hooks
+  invisible()
+}
diff --git a/tests/testthat/test-completion.R b/tests/testthat/test-completion.R
index d2f5a7d7..13beff09 100644
--- a/tests/testthat/test-completion.R
+++ b/tests/testthat/test-completion.R
@@ -118,6 +118,117 @@ test_that("Simple completion is case insensitive", {
     expect_length(result$items %>% keep(~ .$label == "mtcars"), 1)
 })
 
+test_that("Completion of attached package functions works", {
+    skip_on_cran()
+    client <- language_client()
+
+    temp_file <- withr::local_tempfile(fileext = ".R")
+    writeLines(
+        c(
+            "library(jsonlite)",
+            "require('xml2')",
+            "fromJS",
+            "read_xm"
+        ),
+        temp_file)
+
+    client %>% did_save(temp_file)
+
+    result <- client %>% respond_completion(temp_file, c(2, 6),
+        retry_when = function(result) result$items %>% keep(~ .$label == "fromJSON") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "fromJSON"), 1)
+
+    result <- client %>% respond_completion(temp_file, c(3, 7),
+        retry_when = function(result) result$items %>% keep(~ .$label == "read_xml") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "read_xml"), 1)
+
+    temp_file <- withr::local_tempfile(fileext = ".R")
+    writeLines(
+        c(
+            "pacman::p_load(jsonlite, xml2)",
+            "fromJS",
+            "read_xm"
+        ),
+        temp_file)
+
+    client %>% did_save(temp_file)
+
+    result <- client %>% respond_completion(temp_file, c(1, 6),
+        retry_when = function(result) result$items %>% keep(~ .$label == "fromJSON") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "fromJSON"), 1)
+
+    result <- client %>% respond_completion(temp_file, c(2, 7),
+        retry_when = function(result) result$items %>% keep(~ .$label == "read_xml") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "read_xml"), 1)
+})
+
+test_that("Completion of package functions attached in unscoped functions works", {
+    skip_on_cran()
+    client <- language_client()
+
+    temp_file <- withr::local_tempfile(fileext = ".R")
+    writeLines(
+        c(
+            "suppressPackageStartupMessages(library(jsonlite))",
+            "fromJS"
+        ),
+        temp_file)
+
+    client %>% did_save(temp_file)
+
+    result <- client %>% respond_completion(temp_file, c(1, 6),
+        retry_when = function(result) result$items %>% keep(~ .$label == "fromJSON") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "fromJSON"), 1)
+
+    writeLines(
+        c(
+            "suppressPackageStartupMessages({",
+            "  library(jsonlite)",
+            "  require('xml2')",
+            "})",
+            "fromJS",
+            "read_xm"
+        ),
+        temp_file)
+
+    client %>% did_save(temp_file)
+
+    result <- client %>% respond_completion(temp_file, c(4, 6),
+        retry_when = function(result) result$items %>% keep(~ .$label == "fromJSON") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "fromJSON"), 1)
+
+    result <- client %>% respond_completion(temp_file, c(5, 7),
+        retry_when = function(result) result$items %>% keep(~ .$label == "read_xml") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "read_xml"), 1)
+})
+
+test_that("Completion is robust to invalid source", {
+    skip_on_cran()
+    client <- language_client()
+
+    temp_file <- withr::local_tempfile(fileext = ".R")
+    writeLines(
+        c(
+            "library(jsonlite)",
+            "require('xml2')",
+            "require('')",
+            "require('xml2', nonexist_arg = 0)",
+            "fromJS",
+            "read_xm"
+        ),
+        temp_file)
+
+    client %>% did_save(temp_file)
+
+    result <- client %>% respond_completion(temp_file, c(4, 6),
+        retry_when = function(result) result$items %>% keep(~ .$label == "fromJSON") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "fromJSON"), 1)
+
+    result <- client %>% respond_completion(temp_file, c(5, 7),
+        retry_when = function(result) result$items %>% keep(~ .$label == "read_xml") %>% length() == 0)
+    expect_length(result$items %>% keep(~ .$label == "read_xml"), 1)
+})
+
 test_that("Completion of function arguments works", {
     skip_on_cran()
     client <- language_client()
diff --git a/tests/testthat/test-symbol.R b/tests/testthat/test-symbol.R
index f1ae8730..aa378dc5 100644
--- a/tests/testthat/test-symbol.R
+++ b/tests/testthat/test-symbol.R
@@ -36,7 +36,7 @@ test_that("Document Symbol works", {
     )
 })
 
-test_that("Recognize symbols created by delayedAssign()/assign()/makeActiveBinding()", {
+test_that("Recognize symbols created by delayedAssign/assign/makeActiveBinding", {
     skip_on_cran()
     client <- language_client()
 
@@ -59,7 +59,7 @@ test_that("Recognize symbols created by delayedAssign()/assign()/makeActiveBindi
         "makeActiveBinding('a5', function() 5, .GlobalEnv)",
         "makeActiveBinding('a6', function() 6, new.env())",
         "assign(value = '1', x = 'assign1')",
-        "assign('assign2', 2, pos = -1L)",
+        "assign('assign2', 2, pos = -1)",
         "assign('assign3', 3, pos = environment())",
         "assign('assign4', 4, pos = new.env())"
     ), defn_file)
@@ -73,6 +73,32 @@ test_that("Recognize symbols created by delayedAssign()/assign()/makeActiveBindi
     )
 })
 
+test_that("Document symbols are robust to invalid source", {
+    skip_on_cran()
+    client <- language_client()
+
+    defn_file <- withr::local_tempfile(fileext = ".R")
+    writeLines(c(
+        "'' <- 2",
+        "assign('', 3)",
+        "delayedAssign('', 1)",
+        "makeActiveBinding('', 2)",
+        "makeActiveBinding(x, 1)",
+        "assign('var1', 1, nonexist_arg = TRUE)",
+        "delayedAssign('var1', 1, nonexist_arg = TRUE)",
+        "makeActiveBinding('var1', 1, nonexist_arg = TRUE)",
+        "d1 <- 1"
+    ), defn_file)
+
+    client %>% did_save(defn_file)
+    result <- client %>% respond_document_symbol(defn_file)
+
+    expect_setequal(
+        result %>% map_chr(~ .$name),
+        c("d1")
+    )
+})
+
 test_that("Document section symbol works", {
     skip_on_cran()
     client <- language_client(capabilities = list(