This patch alleviates https://github.com/clangd/clangd/issues/1298. Containers in C++ such as `std::vector` or `llvm::SmallVector`, introduce a series of type aliases to adapt to generic algorithms. Currently, If we write an declarator involving expressions with these containers and `auto` placeholder, we probably obtain opaque type alias like following: ```c++ std::vector<int> v = {1, 2, 3}; auto value = v[1]; // hint for `value`: value_type auto *ptr = &v[0]; // hint for `ptr`: value_type * ``` These hints are useless for most of the time. It would be nice if we desugar the type of `value_type` and print `int`, `int *` respectively in this situation. However, things are complicated if user introduces type- alias for brevity: we don't want to make the length of hints be too long! This patch introduces a heuristic method that displays the desugared type for type-aliases that depend on some template parameters or simply reduce to builtin types e.g. int, double.

This patch alleviates https://github.com/clangd/clangd/issues/1298. Containers in C++ such as `std::vector` or `llvm::SmallVector`, introduce a series of type aliases to adapt to generic algorithms. Currently, If we write an declarator involving expressions with these containers and `auto` placeholder, we probably obtain opaque type alias like following: ``` std::vector<int> v = {1, 2, 3}; auto value = v[1]; // hint for `value`: value_type auto *ptr = &v[0]; // hint for `ptr`: value_type * ``` These hints are useless for most of the time. It would be nice if we desugar the type of `value_type` and print `int`, `int *` respectively in this situation. But note we can't always prefer desugared type since user might introduce type-aliases for brevity, where printing sugared types makes more sense. This patch introduces a heuristic method that displays the desugared type that is an alias of template parameter. It merges analogous method `shouldPrintCanonicalType` into `maybeDesugar` as well. Previous commit for shouldPrintCanonicalType: dde8a0fe91cc

This patch alleviates https://github.com/clangd/clangd/issues/1298. Containers in C++ such as `std::vector` or `llvm::SmallVector`, introduce a series of type aliases to adapt to generic algorithms. Currently, If we write an declarator involving expressions with these containers and `auto` placeholder, we probably obtain opaque type alias like following: ```c++ std::vector<int> v = {1, 2, 3}; auto value = v[1]; // hint for `value`: value_type auto *ptr = &v[0]; // hint for `ptr`: value_type * ``` These hints are useless for most of the time. It would be nice if we desugar the type of `value_type` and print `int`, `int *` respectively in this situation. However, things are complicated if user introducesBut note we can't always prefer desugared type- alias for brevity: we don't want to make the length of hints be too long!since user might introduce type-aliases for brevity, where printing sugared types makes more sense. This patch introduces a heuristic method that displays the desugared type type that is an alias of template parameter. It merges for type-aliases that depend on some template parameters or simplyanalogous method `shouldPrintCanonicalType` into `maybeDesugar` as well. reduce to builtin types e.g. int, double. Previous commit for shouldPrintCanonicalType: dde8a0fe91cc