feat: add expr module (#775)

This is (soon) to be used when installing package definitions from
https://github.com/mason-org/mason-registry/. See for example:
https://github.com/mason-org/mason-registry/blob/7df69dd2a73efc3a08520552ca64597d1db5f4fb/packages/go-debug-adapter/package.yaml#L16

1 files changed, 44 insertions, 0 deletions

diff --git a/lua/mason-core/installer/registry/expr.lua b/lua/mason-core/installer/registry/expr.lua
new file mode 100644
index 00000000..be704156
--- /dev/null
+++ b/lua/mason-core/installer/registry/expr.lua
@@ -0,0 +1,44 @@
+local _ = require "mason-core.functional"
+local string_funs = require "mason-core.functional.string"
+local Result = require "mason-core.result"
+
+local M = {}
+
+local parse_expr = _.compose(
+    _.apply_spec {
+        value_expr = _.head,
+        filters = _.drop(1),
+    },
+    _.filter(_.complement(_.equals "")),
+    _.map(_.trim),
+    _.split "|"
+)
+
+---@param str string
+---@param ctx table<string, any>
+function M.eval(str, ctx)
+    return Result.pcall(function()
+        return _.gsub("{{([^}]+)}}", function(expr)
+            local components = parse_expr(expr)
+            local value =
+                assert(ctx[components.value_expr], ("Unable to interpolate value: %q."):format(components.value_expr))
+            return _.reduce(
+                _.apply_to,
+                value,
+                _.map(function(filter_expr)
+                    local filter = setfenv(
+                        assert(
+                            loadstring("return " .. filter_expr),
+                            ("Failed to parse filter: %q."):format(filter_expr)
+                        ),
+                        string_funs
+                    )()
+                    assert(type(filter) == "function", ("Invalid filter expression: %q."):format(filter_expr))
+                    return filter
+                end, components.filters)
+            )
+        end, str)
+    end)
+end
+
+return M