fix(gemini): make thinkingConfig model-aware for 2.5 vs 3.x

Gemini 2.5 uses `thinkingBudget` (and 2.5 Pro cannot disable thinking),
while Gemini 3.x uses `thinkingLevel` ("low"/"high") and cannot be
disabled at all. Translate the plugin's generic `thinkingLevel` per
family instead of sending it through verbatim.

Author: maxronner

lua/codecompanion/adapters/http/gemini.lua

@@ -118,19 +118,46 @@ return {
       return true
     end,
 
+    ---Translate the plugin's generic `thinkingLevel` into a model-appropriate
+    ---`thinkingConfig`. Gemini 2.5 uses `thinkingBudget` (and Pro cannot be
+    ---disabled); Gemini 3.x uses `thinkingLevel` ("low" or "high") and cannot
+    ---be disabled at all. See https://ai.google.dev/gemini-api/docs/thinking.
     ---@param self CodeCompanion.HTTPAdapter
     ---@param params table
     ---@param messages table
     ---@return table
     form_parameters = function(self, params, messages)
-      if self.temp.thinkingLevel then
+      local level = self.temp and self.temp.thinkingLevel
+      if not level then
+        return params
+      end
+
+      local model = self.schema.model.default
+      if type(model) == "function" then
+        model = model(self)
+      end
+
+      local thinking_config
+      if type(model) == "string" and model:match("^gemini%-3") then
+        -- Gemini 3.x: thinkingLevel is "low" or "high"; thinking cannot be disabled.
+        local level_map = { high = "high", medium = "high", low = "low" }
+        local mapped = level_map[level]
+        if mapped then
+          thinking_config = { thinkingLevel = mapped }
+        end
+      elseif type(model) == "string" and model:match("^gemini%-2%.5") then
+        -- Gemini 2.5: thinkingBudget in tokens. 2.5 Pro cannot disable thinking.
         local budgets = { none = 0, low = 1024, medium = 8192, high = 24576 }
-        local budget = budgets[self.temp.thinkingLevel]
-        if budget ~= nil then
-          params.generationConfig = params.generationConfig or {}
-          params.generationConfig.thinkingConfig = { thinkingBudget = budget }
+        local budget = budgets[level]
+        if budget ~= nil and not (budget == 0 and model:match("pro")) then
+          thinking_config = { thinkingBudget = budget }
         end
       end
+
+      if thinking_config then
+        params.generationConfig = params.generationConfig or {}
+        params.generationConfig.thinkingConfig = thinking_config
+      end
       return params
     end,
 

tests/adapters/http/test_gemini.lua

@@ -463,15 +463,16 @@ T["Gemini adapter"]["No Streaming"]["can output for the inline assistant"] = fun
   h.expect_starts_with("Elegant, dynamic.", adapter.handlers.inline_output(adapter, json).output)
 end
 
-T["Gemini adapter"]["form_parameters sets thinkingConfig as object for reasoning models"] = function()
-  local levels = {
+T["Gemini adapter"]["form_parameters maps thinkingLevel to thinkingBudget for Gemini 2.5 Flash"] = function()
+  adapter.schema.model.default = "gemini-2.5-flash"
+  local cases = {
     { level = "none", budget = 0 },
     { level = "low", budget = 1024 },
     { level = "medium", budget = 8192 },
     { level = "high", budget = 24576 },
   }
 
-  for _, tc in ipairs(levels) do
+  for _, tc in ipairs(cases) do
     adapter.temp = { thinkingLevel = tc.level }
     local params = adapter.handlers.form_parameters(adapter, {}, {})
     h.eq(
@@ -482,6 +483,45 @@ T["Gemini adapter"]["form_parameters sets thinkingConfig as object for reasoning
   end
 end
 
+T["Gemini adapter"]["form_parameters refuses to disable thinking on Gemini 2.5 Pro"] = function()
+  adapter.schema.model.default = "gemini-2.5-pro"
+  adapter.temp = { thinkingLevel = "none" }
+  local params = adapter.handlers.form_parameters(adapter, {}, {})
+  -- 2.5 Pro cannot disable thinking; the field must be omitted entirely.
+  h.eq(nil, params.generationConfig)
+
+  adapter.temp = { thinkingLevel = "high" }
+  params = adapter.handlers.form_parameters(adapter, {}, {})
+  h.eq({ thinkingBudget = 24576 }, params.generationConfig.thinkingConfig)
+end
+
+T["Gemini adapter"]["form_parameters maps thinkingLevel for Gemini 3.x reasoning models"] = function()
+  adapter.schema.model.default = "gemini-3.1-pro-preview"
+  local cases = {
+    { level = "high", expected = "high" },
+    { level = "medium", expected = "high" },
+    { level = "low", expected = "low" },
+  }
+
+  for _, tc in ipairs(cases) do
+    adapter.temp = { thinkingLevel = tc.level }
+    local params = adapter.handlers.form_parameters(adapter, {}, {})
+    h.eq(
+      { thinkingLevel = tc.expected },
+      params.generationConfig.thinkingConfig,
+      string.format("thinkingLevel '%s' should map to '%s'", tc.level, tc.expected)
+    )
+  end
+end
+
+T["Gemini adapter"]["form_parameters omits thinkingConfig when disabling on Gemini 3.x"] = function()
+  adapter.schema.model.default = "gemini-3.1-pro-preview"
+  adapter.temp = { thinkingLevel = "none" }
+  -- Gemini 3.x does not support disabling thinking; the field is omitted.
+  local params = adapter.handlers.form_parameters(adapter, {}, {})
+  h.eq(nil, params.generationConfig)
+end
+
 T["Gemini adapter"]["form_parameters does not set thinkingConfig when thinkingLevel is absent"] = function()
   adapter.temp = {}
   local params = adapter.handlers.form_parameters(adapter, {}, {})