"npm create melange-app@latest" failed to install OCaml dependencies to your local opam switch

[zwpdbh]

Failed to install OCaml dependencies to your local opam switch
The scaffolding process failed while running
opam install . --deps-only --yes. Opam is OCaml and ReasonML's package
manager.

opam switch list

zw@zwpdbh:~/code/ocaml-programming/tmp/hello$ opam switch list
#  switch                                     compiler                   description
→  /home/zw/code/ocaml-programming/tmp/hello  ocaml-base-compiler.5.1.1  /home/zw/code/ocaml-programming/tmp/hello
   /home/zw/code/tmp/ocaml_web/hello_ocaml    ocaml-base-compiler.5.1.1  /home/zw/code/tmp/ocaml_web/hello_ocaml
   5.0.0                                      ocaml-base-compiler.5.0.0  5.0.0
   default                                    ocaml-system.4.08.1        default

[NOTE] Current switch has been selected based on the current directory.
       The current global system switch is 5.0.0.

opam install . --deps-only --yes

zw@zwpdbh:~/code/ocaml-programming/tmp/hello$ opam install . --deps-only --yes
Sorry, no solution found: there seems to be a problem with your request.

No solution found, exiting

cat dune-project

cat dune-project
(lang dune 3.14)
; The above stanza specifies the Dune language version being used.


; Declares the use of the Melange compiler with a specific version.
(using melange 0.1)

; Declares the use of the directory-targets extension, useful for managing
; directory-level build targets.
(using directory-targets 0.1)

; Sets the name of the project.
(name hello)

; Indicates whether OPAM files should be automatically generated.
(generate_opam_files true)

; Provides the source location of the project, typically a GitHub repository.
(source
 (github your-username/hello))

; Lists the authors of the project.
(authors "Your Name <[email protected]>")

; Specifies the maintainers of the project, which can be different from authors.
(maintainers "Your Name <[email protected]>")

; Declares the license type under which the project is distributed.
(license MIT)

; Provides a link to the project's documentation.
(documentation https://github.com/your-username/hello)

; The package stanza defines the configuration for an OPAM package.
(package
 (name hello)
 (synopsis "Enter a synopsis of your app here")
 (description "Enter a description of your app here")
; Allows the package to be empty, which can be useful during development.
 (allow_empty)
; Lists the dependencies of the package along with version constraints.
 (depends
  (dune (>= 3.14))
  (melange (>= 3.0.0-51))
  (ocaml (>= 5.1.1))
  opam-check-npm-deps
  ppx_deriving
  (reason (>= 3.11.0))
  (reason-react (>= 0.13.0))
  reason-react-ppx
)
; Tags to categorize or label the package, useful for searches and indexing.
 (tags
  (reasonml, ocaml, melange)))

cat dune

zw@zwpdbh:~/code/ocaml-programming/tmp/hello$ cat dune
; This dune file segment configures the build process for the project,
; focusing on web bundling.

; This stanza excludes the 'node_modules' directory from being
; considered by dune, which is a standard practice to prevent Dune from scanning
; dependency files.
(dirs :standard \ node_modules)

; The 'alias' block named 'all' defines a high-level alias for building the
; entire project. It specifies that the 'all' alias depends on another alias,
; typically named after the bundler being used (e.g., 'vite', 'webpack'). This
; setup allows for easy switching between different bundlers without changing
; the overall build process.
(alias
  (name all)
  (deps
     (alias_rec webpack)))


; The 'rule' block associated with the bundler alias (e.g., 'vite', 'webpack')
; defines the specific steps to build and bundle the web application.
;
; - 'targets (dir dist)' indicates the output directory for the bundled files.
;
; - The 'deps' section lists dependencies like the project alias, bundler config
;   files, and entry HTML file.
;
; - The 'action' specifies the system command to run the bundler, in this case a
;   script from 'node_modules' to run a bundler.
;
; - 'promote (until-clean)' in 'mode' is used for artifact promotion, managing built files.
(rule
  (alias webpack)
   (targets (dir dist))
   (deps
     (alias_rec hello)
     (:webpack ./webpack.config.js)
     (source_tree ./public))
   (action
    (system "../../node_modules/.bin/webpack --mode production \
              --entry ./output/src/App.mjs && cp ./public/index.html dist/index.html"))
   (mode
     (promote (until-clean))))


; The 'melange.emit' block is used to compile ReasonML/OCaml code to JavaScript.
; - 'target output' specifies where the compiled JS files will be placed.
; - It relies on the 'app' library and compiles using specified module systems
;   (here, es6 and mjs).
  (melange.emit
   (target output)
   (alias hello)
   (libraries app)
   (module_systems (es6 mjs)))

[muqiuhan]

Did you dune build @install before running opam install . --deps-only --yes?

[muqiuhan]

Related questions on

• stackoverflow: opam install error "no solution found".
• discuss.ocaml.org: Sorry, no solution found: there seems to be a problem with your request

You may need to update opam.

[dmmulroy]

Also make sure that you run eval $(opam env) before trying to run opam install . --deps-only --yes (Is the error message missing this step/instruction?)

[zwpdbh]

Also make sure that you run eval $(opam env) before trying to run opam install . --deps-only --yes (Is the error message missing this step/instruction?)

Update:
After I installing latest opam from:

bash -c "sh <(curl -fsSL https://raw.githubusercontent.com/ocaml/opam/master/shell/install.sh)"

, I am now using opam 2.1.5.

Then, I could run opam install . --deps-only --yes without problems.
However, it got stuck on new error:

 Failed attempting to build your project with Dune

    The scaffolding process failed while running `opam exec -- dune build`.
    Dune is OCaml and ReasonML's build tool.

    Please try `cd`ing into the project directory created by
    `create-melange-app` and running the following commands:

    eval $(opam env)
    dune build

    If the problem persists, please open an issue at
    github.com/dmmulroy/create-melange-app/issues, and or join our discord for
    help at https://discord.gg/fNvVdsUWHE.

    If you open an issue, please `cd` into the directory created by
    `create-melange-app` and include the output from the following commands:

    `opam switch list`,
    `dune build`,
    `cat dune-project`, and `cat dune`

Then, I follow the instruction:

zw@zw:~/code/ocaml_programming/hello$ eval $(opam env)
zw@zw:~/code/ocaml_programming/hello$ dune build
File "dune", line 32, characters 0-350:
32 | (rule
33 |   (alias webpack)
34 |    (targets (dir dist))
....
41 |               --entry ./output/src/App.mjs && cp ./public/index.html dist/index.html"))
42 |    (mode
43 |      (promote (until-clean))))
asset main.js 200 KiB [emitted] [minimized] (name: main) 1 related asset
orphan modules 585 KiB [orphan] 42 modules
cacheable modules 726 KiB
  modules by path ../../node_modules/react/ 7.98 KiB
    modules by path ../../node_modules/react/*.js 404 bytes 2 modules
    modules by path ../../node_modules/react/cjs/*.js 7.59 KiB 2 modules
  modules by path ../../node_modules/react-dom/ 131 KiB
    ../../node_modules/react-dom/client.js 619 bytes [built] [code generated]
    ../../node_modules/react-dom/index.js 1.33 KiB [built] [code generated]
    ../../node_modules/react-dom/cjs/react-dom.production.min.js 129 KiB [built] [code generated]
  modules by path ../../node_modules/scheduler/ 4.33 KiB
    ../../node_modules/scheduler/index.js 198 bytes [built] [code generated]
    ../../node_modules/scheduler/cjs/scheduler.production.min.js 4.14 KiB [built] [code generated]
  ./output/src/App.mjs + 40 modules 583 KiB [built] [code generated]
webpack 5.91.0 compiled successfully in 1550 ms
cp: cannot stat './public/index.html': No such file or directory

my env:

zw@zw:~/code/ocaml_programming/hello$ opam switch list
#  switch                                 compiler                   description
→  /home/zw/code/ocaml_programming/hello  ocaml-base-compiler.5.1.1  /home/zw/code/ocaml_programming/hello
   default                                ocaml-system.4.08.1        default


zw@zw:~/code/ocaml_programming/hello$ cat dune-project
(lang dune 3.14)
; The above stanza specifies the Dune language version being used.


; Declares the use of the Melange compiler with a specific version.
(using melange 0.1)

; Declares the use of the directory-targets extension, useful for managing
; directory-level build targets.
(using directory-targets 0.1)

; Sets the name of the project.
(name hello)

; Indicates whether OPAM files should be automatically generated.
(generate_opam_files true)

; Provides the source location of the project, typically a GitHub repository.
(source
 (github your-username/hello))

; Lists the authors of the project.
(authors "Your Name <[email protected]>")

; Specifies the maintainers of the project, which can be different from authors.
(maintainers "Your Name <[email protected]>")

; Declares the license type under which the project is distributed.
(license MIT)

; Provides a link to the project's documentation.
(documentation https://github.com/your-username/hello)

; The package stanza defines the configuration for an OPAM package.
(package
 (name hello)
 (synopsis "Enter a synopsis of your app here")
 (description "Enter a description of your app here")
; Allows the package to be empty, which can be useful during development.
 (allow_empty)
; Lists the dependencies of the package along with version constraints.
 (depends
  (dune (>= 3.14))
  (melange (>= 3.0.0-51))
  (ocaml (>= 5.1.1))
  opam-check-npm-deps
  ppx_deriving
  (reason (>= 3.11.0))
  (reason-react (>= 0.13.0))
  reason-react-ppx
)
; Tags to categorize or label the package, useful for searches and indexing.
 (tags
  (reasonml, ocaml, melange)))

zw@zw:~/code/ocaml_programming/hello$ cat dune
; This dune file segment configures the build process for the project,
; focusing on web bundling.

; This stanza excludes the 'node_modules' directory from being
; considered by dune, which is a standard practice to prevent Dune from scanning
; dependency files.
(dirs :standard \ node_modules)

; The 'alias' block named 'all' defines a high-level alias for building the
; entire project. It specifies that the 'all' alias depends on another alias,
; typically named after the bundler being used (e.g., 'vite', 'webpack'). This
; setup allows for easy switching between different bundlers without changing
; the overall build process.
(alias
  (name all)
  (deps
     (alias_rec webpack)))


; The 'rule' block associated with the bundler alias (e.g., 'vite', 'webpack')
; defines the specific steps to build and bundle the web application.
;
; - 'targets (dir dist)' indicates the output directory for the bundled files.
;
; - The 'deps' section lists dependencies like the project alias, bundler config
;   files, and entry HTML file.
;
; - The 'action' specifies the system command to run the bundler, in this case a
;   script from 'node_modules' to run a bundler.
;
; - 'promote (until-clean)' in 'mode' is used for artifact promotion, managing built files.
(rule
  (alias webpack)
   (targets (dir dist))
   (deps
     (alias_rec hello)
     (:webpack ./webpack.config.js)
     (source_tree ./public))
   (action
    (system "../../node_modules/.bin/webpack --mode production \
              --entry ./output/src/App.mjs && cp ./public/index.html dist/index.html"))
   (mode
     (promote (until-clean))))


; The 'melange.emit' block is used to compile ReasonML/OCaml code to JavaScript.
; - 'target output' specifies where the compiled JS files will be placed.
; - It relies on the 'app' library and compiles using specified module systems
;   (here, es6 and mjs).
  (melange.emit
   (target output)
   (alias hello)
   (libraries app)
   (module_systems (es6 mjs)))


zw@zw:~/code/ocaml_programming/hello$ uname -r
5.15.146.1-microsoft-standard-WSL2

[zwpdbh]

I tried to fix error

webpack 5.91.0 compiled successfully in 1550 ms
cp: cannot stat './public/index.html': No such file or directory

I found there is no such public folder in the project directory.
So, I manually create public folder, and move index.html into it.

Then, dune build, without error.
At last, run npm run dev shows: