feat(result): add .try() interface (#804)

2 files changed, 139 insertions, 0 deletions

diff --git a/lua/mason-core/result.lua b/lua/mason-core/result.lua
index 2521fff1..6e7f942c 100644
--- a/lua/mason-core/result.lua
+++ b/lua/mason-core/result.lua
@@ -176,6 +176,38 @@ function Result.run_catching(fn)
     end
 end
 
+---@generic V
+---@param fn fun(try: fun(result: Result): any): V
+---@return Result # Result<V>
+function Result.try(fn)
+    local thread = coroutine.create(fn)
+    local step
+    step = function(...)
+        local ok, result = coroutine.resume(thread, ...)
+        if not ok then
+            -- l'exception! panique!!!
+            error(result, 0)
+        end
+        if coroutine.status(thread) == "dead" then
+            if getmetatable(result) == Result then
+                return result
+            else
+                return Result.success(result)
+            end
+        elseif getmetatable(result) == Result then
+            if result:is_failure() then
+                return result
+            else
+                return step(result:get_or_nil())
+            end
+        else
+            -- yield to parent coroutine
+            return step(coroutine.yield(result))
+        end
+    end
+    return step(coroutine.yield)
+end
+
 function Result.pcall(fn, ...)
     local ok, res = pcall(fn, ...)
     if ok then
diff --git a/tests/mason-core/result_spec.lua b/tests/mason-core/result_spec.lua
index d7d629f5..b2900753 100644
--- a/tests/mason-core/result_spec.lua
+++ b/tests/mason-core/result_spec.lua
@@ -2,6 +2,7 @@ local Result = require "mason-core.result"
 local match = require "luassert.match"
 local spy = require "luassert.spy"
 local Optional = require "mason-core.optional"
+local a = require "mason-core.async"
 
 describe("result", function()
     it("should create success", function()
@@ -212,3 +213,109 @@ describe("result", function()
         )
     end)
 end)
+
+describe("Result.try", function()
+    it("should try functions", function()
+        assert.same(
+            Result.success "Hello, world!",
+            Result.try(function(try)
+                local hello = try(Result.success "Hello, ")
+                local world = try(Result.success "world!")
+                return hello .. world
+            end)
+        )
+
+        assert.same(
+            Result.success(),
+            Result.try(function(try)
+                try(Result.success "Hello, ")
+                try(Result.success "world!")
+            end)
+        )
+
+        assert.same(
+            Result.failure "Trouble, world!",
+            Result.try(function(try)
+                local trouble = try(Result.success "Trouble, ")
+                local world = try(Result.success "world!")
+                return try(Result.failure(trouble .. world))
+            end)
+        )
+
+        local err = assert.has_error(function()
+            Result.try(function(try)
+                local err = try(Result.success "42")
+                error(err)
+            end)
+        end)
+        assert.equals("42", err)
+    end)
+
+    it(
+        "should allow calling async functions inside try blocks",
+        async_test(function()
+            assert.same(
+                Result.success "Hello, world!",
+                Result.try(function(try)
+                    a.sleep(10)
+                    local hello = try(Result.success "Hello, ")
+                    local world = try(Result.success "world!")
+                    return hello .. world
+                end)
+            )
+            local err = assert.has_error(function()
+                Result.try(function(try)
+                    a.sleep(10)
+                    local err = try(Result.success "42")
+                    error(err)
+                end)
+            end)
+            assert.equals("42", err)
+        end)
+    )
+
+    it("should not unwrap result values in try blocks", function()
+        assert.same(
+            Result.failure "Error!",
+            Result.try(function()
+                return Result.failure "Error!"
+            end)
+        )
+
+        assert.same(
+            Result.success "Success!",
+            Result.try(function()
+                return Result.success "Success!"
+            end)
+        )
+    end)
+
+    it("should allow nesting try blocks", function()
+        assert.same(
+            Result.success "Hello from the underworld!",
+            Result.try(function(try)
+                local greeting = try(Result.success "Hello from the %s!")
+                return greeting:format(try(Result.try(function(try)
+                    return try(Result.success "underworld")
+                end)))
+            end)
+        )
+    end)
+
+    it(
+        "should allow nesting try blocks in async scope",
+        async_test(function()
+            assert.same(
+                Result.success "Hello from the underworld!",
+                Result.try(function(try)
+                    a.sleep(10)
+                    local greeting = try(Result.success "Hello from the %s!")
+                    return greeting:format(try(Result.try(function(try)
+                        a.sleep(10)
+                        return try(Result.success "underworld")
+                    end)))
+                end)
+            )
+        end)
+    )
+end)