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

2 files changed, 73 insertions, 0 deletions

diff --git a/tests/mason-core/installer/registry/expr_spec.lua b/tests/mason-core/installer/registry/expr_spec.lua
new file mode 100644
index 00000000..7e662b79
--- /dev/null
+++ b/tests/mason-core/installer/registry/expr_spec.lua
@@ -0,0 +1,57 @@
+local match = require "luassert.match"
+local expr = require "mason-core.installer.registry.expr"
+local Result = require "mason-core.result"
+
+describe("registry expressions", function()
+    it("should eval simple expressions", function()
+        assert.same(Result.success "Hello, world!", expr.eval "Hello, world!")
+
+        assert.same(
+            Result.success "Hello, John Doe!",
+            expr.eval("Hello, {{firstname}} {{ lastname   }}!", {
+                firstname = "John",
+                lastname = "Doe",
+            })
+        )
+    end)
+
+    it("should eval expressions with filters", function()
+        assert.same(
+            Result.success "Hello, MR. John!",
+            expr.eval("Hello, {{prefix|to_upper}} {{  name | trim   }}!", {
+                prefix = "Mr.",
+                name = " John   ",
+            })
+        )
+
+        assert.same(
+            Result.success "Hello, Sir MR. John!",
+            expr.eval("Hello, {{prefix|to_upper | format 'Sir %s'}} {{  name | trim   }}!", {
+                prefix = "Mr.",
+                name = " John   ",
+            })
+        )
+    end)
+
+    it("should reject invalid values", function()
+        assert.is_true(
+            match.matches [[^.*Unable to interpolate value: "non_existent"%.$]](
+                expr.eval("Hello, {{non_existent}}", {}):err_or_nil()
+            )
+        )
+    end)
+
+    it("should reject invalid filters", function()
+        assert.is_true(
+            match.matches [[^.*Invalid filter expression: "whut"%.$]](
+                expr.eval("Hello, {{ value | whut }}", { value = "value" }):err_or_nil()
+            )
+        )
+
+        assert.is_true(
+            match.matches [[^.*Failed to parse filter: "wh%-!uut"%.$]](
+                expr.eval("Hello, {{ value | wh-!uut }}", { value = "value" }):err_or_nil()
+            )
+        )
+    end)
+end)
diff --git a/tests/mason-core/result_spec.lua b/tests/mason-core/result_spec.lua
index 1d8f36fb..d7d629f5 100644
--- a/tests/mason-core/result_spec.lua
+++ b/tests/mason-core/result_spec.lua
@@ -195,4 +195,20 @@ describe("result", function()
         assert.equals("Error", failure:get_or_nil())
         assert.spy(chain).was_not_called()
     end)
+
+    it("should pcall", function()
+        assert.same(
+            Result.success "Great success!",
+            Result.pcall(function()
+                return "Great success!"
+            end)
+        )
+
+        assert.same(
+            Result.failure "Task failed successfully!",
+            Result.pcall(function()
+                error("Task failed successfully!", 0)
+            end)
+        )
+    end)
 end)